HK1191144A - Apparatus and methods for adjusting voltage controlled oscillator gain - Google Patents

Description

Apparatus and method for adjusting gain of voltage controlled oscillator

Technical Field

The disclosed technology relates to electronic systems, and in particular to voltage controlled oscillators.

Background

Electronic components such as wideband synthesizers can support a wide range of output frequencies. To produce a range of output frequencies, an electronic oscillator configured to oscillate over a range of frequencies may be used, such as a Voltage Controlled Oscillator (VCO). In some applications, a wide range of output frequencies may be desired. For example, an output signal in the range from about 400MHz to 6.3GHz may be desired. To ensure high performance over the entire frequency range, more than one VCO may be implemented. In such an implementation, each VCO may be dedicated to a particular frequency band, which may overlap with the frequency band of another VCO. Tuning the frequency of a VCO may affect the gain of the corresponding VCO. This may result in sub-optimal performance when tuning the frequency of the VCO and altering the corresponding gain. For systems including multiple VCOs, compensating for changes in VCO gain may be more complex. Accordingly, there is a need for improved systems and methods for compensating for VCO gain variations.

Disclosure of Invention

The methods and apparatus described in the claims each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of the invention, some salient features will now be discussed briefly.

One aspect of the present disclosure is a method of adjusting a gain of a Voltage Controlled Oscillator (VCO). The method includes selecting a VCO gain adjustment model based on the VCO gain indicator. The method also includes obtaining VCO gain adjustment model parameters from the memory. The charge pump control value is calculated using the VCO gain adjustment model parameters. The total loop gain of the phase locked loop is dynamically adjusted using the charge pump control value.

According to some implementations, the VCO gain indicator indicates the VCO output frequency. In various implementations, the VCO gain indicator indicates a capacitance value in a tunable capacitance circuit configured to control a frequency of the VCO output. In some of these implementations, selecting the gain adjustment model includes comparing the capacitance value to a threshold value.

According to many implementations, the gain adjustment parameters include a slope and an offset. In some implementations, obtaining the VCO gain adjustment model parameters is based on a VCO selected from a plurality of VCOs.

In certain implementations, the method further includes calculating VCO gain model parameters and storing the VCO gain model parameters to memory.

Another aspect of the present disclosure is an apparatus that includes a charge pump controller. The charge pump controller includes a memory and an arithmetic logic unit. The memory is configured to store VCO gain model parameters and thresholds. The arithmetic logic unit is configured to: selecting a VCO gain model based on a comparison of the VCO gain indicator to at least one threshold value stored in memory; obtaining VCO gain model parameters corresponding to the selected VCO gain model from the memory; and calculating a charge pump control value using the VCO gain model parameters.

In some implementations, the VCO gain indicator indicates the VCO output frequency. According to many implementations, the VCO gain indicator indicates a capacitance value in a circuit configured to control the VCO output frequency, and the threshold value stored in the memory represents a threshold capacitance value. According to various implementations, the VCO gain model parameters correspond to a plurality of VCOs. In some of these implementations, the arithmetic logic unit is further configured to obtain VCO gain model parameters corresponding to a selected one of the VCOs. In some implementations, the VCO gain model parameters include at least a slope and an offset.

According to many implementations, the apparatus includes a VCO. In some of these implementations, the arithmetic unit is configured to dynamically cause the gain of the VCO to be adjusted based on the charge pump current control value. In various implementations, the VCO gain model represents a portion of a VCO correction curve representing a VCO output frequency indicator versus a charge pump current control value.

According to some implementations, the apparatus further includes a phase locked loop including a VCO and a charge pump configured to: a charge pump current control value is received from the processor and the gain of the VCO is adjusted based on the charge pump current control value.

According to some implementations, the charge pump controller is further configured to calculate VCO gain model parameters and at least one threshold value, and store the VCO gain model parameters and the at least one threshold value to the memory. In some of these implementations, the charge pump controller is configured to calculate VCO gain model parameters in response to detecting the calibration event.

In certain implementations, the memory includes at least one lookup table configured to store at least one of the threshold values and the VCO gain model parameters.

Yet another aspect of the disclosure is an apparatus, comprising: means for selecting a VCO gain model based on a comparison of the VCO gain indicator to at least one threshold value stored in memory; means for obtaining VCO gain model parameters corresponding to the selected VCO gain model from a memory; and means for calculating a charge pump current control value using the VCO gain model parameters.

In certain implementations, the apparatus is a base station.

For purposes of summarizing the disclosure, certain aspects, advantages, and novel features of the invention have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

Drawings

Fig. 1 schematically depicts an apparatus that may include a phase-locked loop.

Fig. 2 schematically illustrates a phase locked loop according to an embodiment.

Fig. 3B illustrates the relationship between gain and capacitance in a Voltage Controlled Oscillator (VCO) controlled by the example tuning capacitance circuit shown in fig. 3A. Fig. 3C illustrates the relationship between gain and frequency in a synthesizer having multiple VCOs.

Figure 4 is a flow diagram of an illustrative method of compensating for VCO gain variations in accordance with one embodiment.

Figure 5 is a block diagram of a circuit that may compensate for VCO gain variation according to an embodiment.

Figure 6 schematically illustrates a circuit that can compensate for VCO gain variations, according to another embodiment.

Fig. 7 is a graph of an example VCO correction curve.

Figure 8 is a flow diagram of an illustrative method of calibrating VCO gain adjustment model parameters, according to an embodiment.

Detailed Description

In general, aspects of the present disclosure relate to adjusting the gain of an electronic oscillator, such as a Voltage Controlled Oscillator (VCO). For purposes of illustration, a description will be provided with reference to a VCO, although the principles and advantages may be applied to any electronic oscillator. The VCO may be part of a Phase Locked Loop (PLL) that may be included in a transmit and/or receive path of a mobile device or base station, such as a cellular telephone. The gain of the VCO may be affected by many factors, such as the VCO output frequency and/or temperature. However, the overall gain of the closed loop within the PLL may help achieve best performance and/or stable loop bandwidth. Thus, compensating for factors that affect the VCO gain may advantageously improve VCO performance, which in turn may also improve the performance of any device that includes a VCO.

In accordance with the disclosure provided herein, the VCO gain may be dynamically compensated such that the overall loop gain of the phase locked loop remains substantially constant. This may include, for example, controlling the charge pump current based on an indicator of VCO gain, such as an indicator of VCO output frequency. The VCO gain correction curve may be divided into a plurality of VCO gain models. A particular VCO gain model may be selected based on the VCO gain indicator. For implementations including multiple individual VCOs, the VCO gain model may be chosen for the selected VCO. From the VCO gain model parameters and the indicator of VCO gain, a charge pump current value may be calculated. The charge pump current value may then be used to adjust the overall loop gain of the phase locked loop.

Among other things, the methods, apparatus, and computer readable media described herein for compensating for VCO gain variation can implement one or more of the following advantageous features. First, the optimum charge pump current can be provided over the entire VCO output frequency range. Second, the charge pump controller may only program the memory (e.g., look-up table) once, and may not need to be calculated and programmed after each frequency change. Third, for architectures with multiple VCOs, the charge pump controller may not need to read the active VCO in order to calculate the charge pump current control value.

Any of the methods, apparatus, and computer readable media for adjusting VCO gain described herein may be implemented in various electronic devices, such as a base station or a mobile device. Fig. 1 schematically depicts a device 11. The apparatus 11 may be a base station. In other embodiments, the apparatus 11 may be a mobile device. Examples of mobile devices include, but are not limited to, cellular phones (e.g., smart phones), notebook computers, tablet computers, Personal Digital Assistants (PDAs), e-book readers, and portable digital media players. For example, in certain embodiments, the apparatus 11 may be a multi-band and/or multi-mode device, such as a multi-band/multi-mode mobile phone or a multi-band/multi-mode base station configured to communicate using, for example, global system for mobile communications (GSM), Code Division Multiple Access (CDMA), 3G, 4G, and/or Long Term Evolution (LTE).

The apparatus 11 may include a transceiver component 13 configured to generate RF signals for transmission via an antenna 14, and to receive incoming RF signals from the antenna 14. The transceiver 13 may also include one or more Phase Locked Loops (PLLs) 17 in the receive and/or transmit paths. Each PLL17 may each include one or more VCOs configured to generate an output signal within a frequency band. For example, a PLL may be used to up-convert a signal in a transmit path and/or down-convert a signal in a receive path. Although the example phase locked loop 17 is illustrated in the context of the transceiver 13, any of the components of the phase locked loop described herein may be implemented in a receiver, transmitter, and/or other electronic system that requires a voltage controlled oscillator.

One or more output signals from transceiver 13 may be provided to switching assembly 12 using one or more transmission paths 15, which transmission paths 15 may be output paths associated with different frequency bands and/or different power outputs, such as amplification associated with different power output configurations (e.g., low power output and high power output) and/or amplification associated with different frequency bands. In addition, transceiver 13 may receive signals from switching assembly 12 using one or more receive paths 16.

Switching component 12 may provide a number of switching functions associated with the operation of apparatus 11, including, for example, switching between different frequency bands, switching between different power modes, switching between transmit and receive modes, or some combination thereof. However, in some implementations, switching component 12 may be omitted. For example, the apparatus 11 may comprise a separate antenna for each transmit and/or receive path.

In certain embodiments, a control component 18 may be included, and the control component 18 may be configured to provide various control functions associated with operation of the switching component 12, the power amplifier 17, and/or one or more other operating components. Further, the apparatus 11 may include a processor 20 for facilitating implementation of various processes. The processor 20 may be configured to operate using instructions stored on the non-transitory computer readable medium 19. The processor 20 may implement any combination of the features of the transceiver 13.

Fig. 2 schematically illustrates an example phase locked loop 100. A phase-locked loop (PLL) may be a closed-loop, frequency-controlled system based on a phase difference between an input reference signal (e.g., an input clock) and a feedback signal (e.g., a feedback clock) of a controlled oscillator. The PLL may generate an output signal having a phase related to the phase of the input reference signal. The PLL may be implemented by an electronic circuit. As shown, the phase locked loop 100 includes a reference divider (divider) 102, a phase frequency detector 104, a charge pump 106, a loop filter 108, a VCO110, a PLL divider 112, an output divider 114, and an output amplifier 116. A charge pump controller 120 may also be included. It will be appreciated that fewer or more components may implement a PLL. For example, in some instances, the reference divider 102, the output divider 114, and the output amplifier 116 may not be included.

The reference divider 102 may receive an input clock and generate a reference clock signal having a frequency of the input clock divided by M. Phase frequency detector 104 may receive the reference clock signal and align an edge (e.g., a rising edge) of the reference clock with the feedback clock generated by PLL divider 112. The PLL divider 112 may generate a feedback clock from the VCO output. The feedback clock may have a frequency of the VCO divided by N. The phase frequency detector 104 may detect the relative difference in phase and frequency between the reference clock and the feedback clock.

Based on whether the feedback clock frequency lags or leads the reference frequency, the phase frequency detector may provide one or more control signals to control the charge pump 106 indicating that the VCO110 should operate at a higher or lower frequency. However, the VCO frequency may remain the same when the feedback clock and the reference clock are aligned. If the charge pump 106 receives an indicator that the frequency of the VCO should be increased, then current may be driven to the loop filter 108. Conversely, if the charge pump 106 receives an indicator that the VCO frequency should be decreased, current may be drawn from the loop filter 108. Further, the charge pump 106 may generate a VCO gain adjustment indicator, which may be used to adjust the gain of the VCO output to the VCO110 via the loop filter 108. The gain of the VCO output may be adjusted while maintaining a constant VCO output frequency.

The loop filter 108 may generate a control voltage based on one or more signals from the charge pump 106. The control voltage may be used to bias the VCO 110. Based on the control voltage, the VCO110 may oscillate at a higher or lower frequency, which may affect the phase and frequency of the feedback clock. Once the reference clock and the feedback clock have substantially the same phase and frequency, the VCO110 may stabilize. The loop filter 108 may filter out jitter by removing glitches from the charge pump 106, thereby preventing voltage overshoot.

In some implementations, the VCO110 may include multiple individual VCOs. For example, in some implementations, 2 to 8 VCOs may be included in the VCO 110. In implementations having multiple VCOs, each of the multiple VCOs may generate an output within a particular frequency band that overlaps with a corresponding frequency band of another VCO. In the case of multiple VCOs, a single VCO of VCO110 may be selected to generate a VCO output based on the desired output frequency. In this way, a wide range of output frequencies can be generated and high performance over the entire range of VCO output frequencies.

The VCO output may be provided to PPL divider 112 and output divider 114. The output divider 114 may generate an output divider clock having an output divider signal that is less than the VCO output frequency. The output amplifier 116 may receive the output divider clock and provide an amplified output signal.

Further, the PLL100 includes a charge pump controller 120. Any combination of the features of any of the charge pump controllers described herein may be implemented on a processor, such as processor 20 of fig. 1. In some examples, the processor including the PLL100 and the charge pump controller 120 may be a synthesizer, such as a wideband synthesizer. The charge pump controller 120 may be implemented on the same integrated circuit or on a separate integrated circuit from one or more of the other illustrated components of the PLL 100. Further, the charge pump controller 120 can be implemented using any suitable combination of analog and/or digital circuitry.

The charge pump controller 120 can provide a charge pump current control value to the charge pump 106, which can be used to compensate for VCO gain variation K_v. For example, based on the charge pump current control value, the charge pump 106 may send a VCO gain adjustment indicator to the VCO110 via the loop filter 108 to adjust the gain of the VCO output. The VCO gain adjustment indicator may then adjust the gain of the VCO output without changing the VCO output frequency. In some instances, the VCO gain adjustment indicator may control the charge pump current by switching in one or more capacitive circuit elements in parallel with the charge pump output, which may affect the overall loop gain. More details regarding the charge pump controller 120 will be provided later with reference to fig. 4-6.

VCO gain K_vMay vary based on a parameter indicative of the VCO frequency. For example, the parameter for controlling the VCO frequency may also indicate the VCO gain K_v. Fig. 3A provides an example circuit that can control the VCO frequency. In particular, fig. 3A illustrates a tunable capacitance circuit 130 that can adjust the VCO output frequency. In implementations where the PLL includes multiple separate VCOs, a separate tunable capacitance circuit 130 may be used for each VCO. Although the capacitance of the tunable capacitance circuit is described as an example parameter indicative of VCO gain, other parameters may alternatively or additionally be used as indicators of VCO gain and/or VCO output frequency.

Tunable capacitance circuit 130 may include a plurality of capacitors 132a-132h and an inductor 134 that may form an LC tank. The effective capacitance of the LC tank circuit, which may represent a combined capacitance of tunable capacitive elements that are part of the LC tank circuit, may be adjusted using a capacitance control signal that may add and/or remove additional capacitance from the effective capacitance. For example, each capacitor 132a-132g of the LC circuit shown in FIG. 3A may be based on turning off and/or on, such as by a crystalCapacitance control signals CAP _ CTRL [0:6 ] of switches of transistor]Is selectively included in or excluded from the effective capacitance of the LC tank. In case of an increase in capacitance, the VCO frequency may be decreased. Conversely, with reduced capacitance, the VCO frequency may be increased. The resonant frequency ω of the VCO may be proportional to the inverse of the square root of the inductance L times the capacitance C, e.g., as shown by the following equation:

FIG. 3B illustrates VCO gain K in the example tunable capacitance circuit shown in FIG. 3A_vAnd the effective capacitance. As shown in FIG. 3B, the VCO gain K_vMay have an anti-log relationship with the effective capacitance of the tunable capacitance circuit. As the effective capacitance increases, an inverse logarithmic VCO gain K is observed_vIs reduced.

Further, in implementations with multiple VCOs, the VCO gain K_vThe frequency curve for the VCO may include a plurality of segments corresponding to each VCO. Each of the plurality of segments may have a similar shape and represent a VCO gain K_vAnd VCO frequency. FIG. 3C illustrates VCO gain K in a synthesizer having multiple VCOs_vAnd VCO frequency. As shown in fig. 3C, K corresponds to each VCO_vA similar relationship may be illustrated for a portion of the VCO frequency curve. However, the corresponding slope and offset (which may also be referred to as "intercept") for each individual VCO may be different. This may be due to differences in VCO architecture.

The overall loop gain may advantageously be kept substantially constant in order to improve performance and/or stabilize the loop bandwidth. One way to keep the total loop gain constant is to compensate for VCO gain variations. This may be accomplished, for example, by adjusting the current in a charge pump (e.g., charge pump 106 of fig. 2) of a phase locked loop using a charge pump controller (e.g., charge pump controller 120 of fig. 2).

Fig. 4 is a flow diagram of an illustrative method 200 of compensating for VCO gain variations. Any combination of the features of method 200 may be embodied in a non-transitory computer readable medium and stored in non-volatile memory. When executed, the non-transitory computer-readable medium may cause some or all of the method 200 to be performed. It will be appreciated that any of the methods described herein may include more or fewer operations, and that the operations may be performed in any order as appropriate.

The method 200 may adjust the VCO gain to stabilize the overall loop gain of the phase locked loop when any factor that may affect the VCO gain changes. One example of a factor that may affect VCO gain is the VCO output frequency as shown in fig. 3C. Although more detail will be provided with reference to the VCO output frequency for purposes of illustration, other factors may be used as indicators of VCO gain in accordance with the methods and systems described herein. For example, the VCO gain may be temperature dependent, and the total loop gain of the phase locked loop may be adjusted to account for temperature changes, e.g., as determined via a temperature sensor.

By performing the method 200, the overall loop gain of the phase locked loop may be adjusted at a portion that is not factory calibrated with respect to charge pump current for factors that may affect VCO gain, such as VCO output frequency range. Furthermore, the method 200 does not require additional programming related to factory calibration by the controller prior to activation. Furthermore, when compensating for the effect on VCO gain due to VCO output frequency, when performing the method 200 in a PLL with multiple VCOs, the controller may not need to obtain additional information about which VCO is selected if the VCO frequency is in an overlapping frequency range in which more than one VCO may generate the VCO frequency.

At block 202, a VCO gain adjustment model may be selected based on the indicator of VCO gain. The VCO gain indicator may indicate any factor that may affect the VCO gain, including, among other things, the VCO output frequency and/or temperature. Because the VCO gain may depend on an indicator of the VCO frequency (e.g., as shown in fig. 3B), the charge pump controller may adjust the charge pump current to compensate for changes in the VCO gain due to changes in the indicator of the VCO frequency. In some instances, the indicator of the VCO frequency may be an effective capacitance in a tunable capacitance circuit used to control the VCO frequency.

The VCO gain correction curve may correct for changes in VCO gain based on an indicator of VCO output frequency or other indicator that VCO gain may change. Thus, the charge pump controller may be provided with a value on the VCO gain correction curve to cause the charge pump to compensate for the effect of the VCO frequency on the VCO gain. Although the VCO gain correction curve corresponding to the VCO may not be linear, the VCO gain correction curve may be divided into a plurality of piecewise linear gain adjustment models. Each of these models may correspond to a range of frequency indicator values. Accordingly, the VCO gain adjustment model may be selected based on a comparison of the indicator of VCO frequency to one or more thresholds, which may represent values that separate the VCO gain correction curve into separate linear gain adjustment models. In some implementations with multiple VCOs, the thresholds may be chosen so that they are the same for each separate VCO.

The VCO gain adjustment model may include gain adjustment model parameters. VCO gain adjustment model parameters may be obtained at block 204. The model parameters may be any parameters from which a gain adjustment model may be created. For example, the model parameters may include the slope and intercept of the linear gain adjustment model. The gain model parameters may be stored in memory and obtained by reading from memory. In implementations with multiple VCOs, gain model parameters may be obtained for the VCO selected to generate the VCO output. For example, gain model parameters corresponding to each VCO may be retrieved from memory, and the gain model parameters for the selected VCO may be obtained using logic that selects the gain model parameters for the selected VCO.

Using the gain adjustment model parameters, a charge pump current control value may be calculated at block 206. For example, using the VCO frequency indicator, the charge pump current control value may be based on the slope times the frequency indicator plus an offset for the linear gain adjustment model. The charge pump current control value may then be provided to a charge pump that controls the overall loop gain of the phase locked loop.

At block 208, the total loop gain of the phase locked loop may be dynamically adjusted using the charge pump current control value. The charge pump may compensate for VCO gain variations without substantially altering the VCO frequency. In this way, the overall loop gain of the phase locked loop can be stabilized. As a result, the PLL may operate with better performance and/or with a stable loop bandwidth.

Fig. 5 is a block diagram of a charge pump controller 120a, which is one example of the charge pump controller 120 of fig. 2. The charge pump controller 120a may be included in a processor, such as a synthesizer. In some examples, the processor may include a PLL including a charge pump controlled by the charge pump controller 120 a. For example, the charge pump controller 120a may compensate for VCO gain variations according to any combination of the features of the method 200. The charge pump controller 120 may include a memory 222, a model selection block 224, a VCO selection block 226, and a charge pump current control calculator 228. It will be appreciated that the memory 222, the model selection block 224, the VCO selection block 226, and the charge pump current control calculator 228 may each be implemented in hardware. The charge pump controller 120 can control the VCO gain based on any indicator of VCO gain, such as an indicator of VCO output frequency. In implementations with multiple VCOs, the charge pump controller 120a may also control the overall loop gain of the phase locked loop based on the selected VCO.

Memory 222 may include RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. The memory 222 may store threshold and gain adjustment model parameters. In some instances, the memory may include one or more look-up tables. In this manner, the threshold and gain adjustment model parameters may be stored locally in the charge pump controller 120a such that the values need not be retrieved and/or retrieved from remote memory each time they are used.

Model selection 224 may select a portion of the VCO gain correction curve based on the VCO frequency. The model selection 224 may obtain one or more thresholds from the memory 224 and obtain an indicator of VCO gain, such as VCO output frequency, from the VCO. Model selection 224 may then compare the indicator of VCO gain to one or more thresholds. Based on the one or more comparisons, a VCO gain adjustment model may be selected that represents a portion of the VCO gain correction curve. For example, the selected VCO gain adjustment model may correspond to the VCO output frequency. The model selection 224 may provide a model selection indicator to the charge pump current control calculator 228 based on the VCO gain indicator, the model selection indicator indicating which VCO gain adjustment model to use to alter the overall loop gain of the phase locked loop. For example, a gain adjustment model may be selected based on a particular VCO output frequency. Model selection 224 may be implemented in an Arithmetic Logic Unit (ALU), such as ALU234 of fig. 6.

VCO select 226 may select one of a plurality of individual VCOs. For example, multiple VCOs may be used to generate an output signal across a wide output frequency range, with each individual VCO generating an output signal for a portion of the output frequency range. VCO selection 226 may obtain VCO gain adjustment model parameters corresponding to a plurality of VCOs from memory 224. For example, the gain adjustment parameters may include a slope and an offset. VCO selection 226 may also obtain an indicator of the selected VCO from the VCO. The indicator of the selected VCO may indicate which of the plurality of VCOs is used to generate the VCO output at the VCO frequency. Based on the indicator of the selected VCO, the VCO selection 226 may provide VCO gain adjustment parameters corresponding to the selected VCO to the charge pump current control calculator 228. VCO selection 226 may be implemented in an ALU, such as ALU234 of fig. 6.

The charge pump current control calculator 228 may calculate a charge pump current control value based on the model selection indicator from the model selection 224 and the VCO gain adjustment parameter from the VCO selection 226. Using this data, the charge pump current control calculator 228 can dynamically calculate a charge pump current control value for a selected VCO at a particular frequency. Using the charge pump current control value, a charge pump of the PLL (e.g., charge pump 106 of fig. 3) may compensate for VCO gain variations to stabilize the overall loop gain of the PLL. The charge pump current control calculator 228 may be implemented in an ALU, such as ALU234 of fig. 6.

Fig. 6 schematically illustrates a charge pump controller 120b that can be dynamically adjusted for VCO gain variations. The charge pump controller 120b is another example of the charge pump controller 120 of fig. 2, which may be implemented in a processor such as a synthesizer. In some examples, charge pump controller 120b can also correspond to charge pump controller 120 a. The charge pump controller 120b can include a lookup table component 232 and an Arithmetic Logic Unit (ALU) 234.

As shown, the lookup table component 232 includes three lookup tables: a threshold lookup table 242, a slope lookup table 244, and an offset lookup table 246. Because the amount of data and/or the length of the data entries may be different, each of the lookup tables 242, 244, and 246 may have a different size. Alternatively, the three look-up tables may also be implemented by any number of look-up tables. In some instances, the lookup table component 232 may also store additional information for each VCO, including, for example, a maximum VCO output frequency, a minimum output frequency, a maximum VCO gain, a minimum VCO gain, and/or a range of charge pump current control values. Table 1 provides examples of some of the values that may be stored in the lookup table component 232.

Threshold value
							TH1	TH2	TH3	TH4	TH5	TH6	TH7
18	35	51	67	83	98	113
							VCO	1	2	3	4	5	6
Slope of
							x<TH1	0.875	0.625	1.125	1.625	1.125	1.75
TH1<=x<TH2	0.9	0.7	1.2	1.7	1.3	2.05
							TH2<=x<TH3	0.95	0.8	1.3	1.8	1.5	2.375
TH3<=x<TH4	1.1	0.925	1.45	1.925	1.75	2.75
							TH4<=x<TH5	1.25	1.1	1.6	2.1	2.1	3.15
TH5<=x<TH6	1.5	1.325	1.75	2.3	2.7	3.5
							TH6<=x<TH7	1.9	1.5	2.05	2.8	3.35	4.1
TH7<=x	2.5	1.85	2.3	3.3	4.0	4.8
							Offset amount
x<TH1	1.25	1.25	1	1.75	1.5	2.25
							TH1<=x<TH2	1.51	1.44	1.34	2.24	1.84	2.78
TH2<=x<TH3	1.78	1.65	1.70	2.75	2.23	3.39

TH3<=x<TH4	2.02	1.85	2.02	3.20	2.60	3.98
							TH4<=x<TH5	2.24	2.03	2.31	3.58	2.95	4.53
TH5<=x<TH6	2.43	2.20	2.55	3.90	3.27	5.01
							TH6<=x<TH7	2.58	2.33	2.73	4.13	3.54	5.36
TH7<=x	2.73	2.45	2.89	4.35	3.81	5.68

TABLE 1

The values stored in the lookup table component 232 may provide all data to calculate the charge pump current control value based on an indicator of VCO gain (e.g., an indicator of VCO frequency) and an indicator of the selected VCO. For example, some or all of the values stored in the lookup table component 232 may correspond to a piecewise linear representation of the VCO gain correction curve illustrated in fig. 7. The VCO gain correction curves C1, C2, and C3 of fig. 7 may correspond to charge pump current control values that may be used to keep the overall loop gain of the phase locked loop substantially constant for different capacitance values in the tunable capacitance circuit used to generate the VCO output signal. Although three VCO gain correction curves are shown in fig. 7, one VCO gain correction curve may be determined for each VCO in the PLL. More details regarding an example of obtaining values in the lookup table component 232 will be provided with reference to FIG. 8.

The thresholds TH1-TH7 of fig. 7 may be determined such that a portion of each VCO gain correction curve C1-C3 may be represented by a linear function. Thus, for portions of the VCO gain correction curve having steeper slopes, the thresholds may be closer together. For example, the difference between the thresholds TH7 and TH6 is less than the difference between the thresholds TH1 and TH 2. Furthermore, because n thresholds may divide the curve into n +1 partitions, there may be one less threshold than the number of linear partitions of the VCO gain correction curve. For example, 7 thresholds may be used to divide the VCO gain correction curve into 8 linear partitions. The same threshold TH1-TH7 may be used for each VCO gain correction curve. The threshold may indicate the VCO frequency. For example, in the example implementations of fig. 5-6, the threshold value may correspond to a capacitance value in a tunable capacitance circuit used to generate the VCO output. Each of the thresholds may be stored in the threshold lookup table 242 of fig. 6, and table 1 provides example thresholds. The size of the threshold lookup table 242 may be based on the number of stored thresholds multiplied by the number of bits used to store each threshold. Thus, the threshold lookup table 242 may be larger for more accurate thresholds represented by more bits.

Each partition of the VCO gain correction curves C1-C3 may be represented by a linear VCO tuning model. Because these models are linear, they can be represented by slope and intercept. The charge pump gains GN1-GN3 may represent the difference between the values calculated by the VCO tuning model and the corresponding intercept or offset. The slope may approximate the slope of the VCO gain correction curve for a particular partition. The slope of each VCO may be stored in a slope lookup table 244. The size of the slope lookup table 244 may be based on the number of VCOs and the number of bits used to represent the value of the slope of each VCO. The intercept or offset may represent the point at which the VCO gain correction curve intersects the y-axis. The offset for each VCO may be stored in an offset lookup table 246. The size of the offset lookup table 246 may be based on the number of VCOs and the number of bits used to represent the value of the slope of each VCO. In table 1, example slope and offset values corresponding to VCO gain adjustment models for each of the 6 VCOs are provided. In another implementation, one offset for each VCO may be stored, and the offset corresponding to each VCO gain model may be derived from the stored offsets.

The arithmetic logic unit 234 may read a value from the lookup table component 232. For example, a particular VCO gain adjustment model used to calculate the charge pump current control value may be determined by comparing the capacitance value of a tunable capacitance circuit controlling the VCO output frequency to the threshold values in the threshold lookup table 242 using one or more comparators 252. The capacitance value may be compared to any combination of threshold values from the look-up table 242. From one or more comparisons, a model selection indicator may be generated. The slope and offset corresponding to each portion of each VCO gain correction curve may be read from slope lookup table 244 and offset lookup table 246, respectively. For example, one or more multiplexers 254 may be used to select a value corresponding to a selected VCO to generate a VCO output based on an indicator from the VCO.

The model selection indicator may be used to select a slope and offset corresponding to a selected VCO gain adjustment model, the selected VCO gain adjustment modelThe pattern may correspond to the VCO output frequency. For example, the CHARGE PUMP current correction value CHARGE PUMP CONTROL is calculated by multiplying the capacitance segment selection CAP _ SEL by the selected slope SLP _ VCO using a multiplier 256. Then, for example, the selected offset OFS _ VCO can be added using an adder 257. The capacitance segment selection, CAP _ SEL, is obtained by comparing a current capacitance control value (control) to one or more of the thresholds. In some implementations, the capacitance segment selection CAP _ SEL multiplied by the selected slope SLP _ VCO may be divided by a predetermined multiple (e.g., 8) for scaling purposes and/or computational simplicity. This may be done before or after adding the selected offset. The division/scaling may be implemented using divider 258. Divider 258 may shift the value by 3 bits, resulting in a division by 8. In this implementation, the charge pump current control value may be represented by the following equation:

in some examples, the bypass function may pass a predetermined charge pump current control value in place of the charge pump current control value calculated by the arithmetic logic unit 234. One way to implement the bypass function is to use a multiplexer 262 to select the charge pump current control value calculated with a predetermined charge pump current control value using a bypass signal.

The VCO gain adjustment model parameters used to calculate the charge pump current control value may be obtained using a number of different methods. For example, the VCO gain adjustment model parameters may be obtained by one calibration during factory calibration. Alternatively, the VCO gain model adjustment parameters may be automatically calibrated to account for the additional variations.

Fig. 8 is a flow diagram of an illustrative method 300 of calibrating VCO gain adjustment model parameters, according to an embodiment. The method 300 may begin when a calibration event is detected at block 302. A calibration event is any event that may indicate that calibration may occur. For example, the calibration event may be to power up a system that includes a VCO and charge pump control. As another example, the calibration event may be when the component is operating above a predetermined temperature for a predetermined period of time. The calibration event may trigger a calibration finite state machine.

At block 304, a frequency range and a maximum VCO gain may be determined for each VCO. For example, the calibration finite state machine may tune a tunable capacitance circuit used to generate the VCO frequency over a tunable capacitance range and measure an indicator of the output frequency range and the VCO gain. The VCO frequency may be proportional to the effective capacitance in the tunable capacitance circuit used to generate the VCO output multiplied by the frequency of the reference clock provided to the phase locked loop. The charge pump control current value range for each VCO may be proportional to the maximum VCO frequency divided by the cube of the minimum VCO frequency. This process may be repeated for each individual VCO in a system including more than one VCO. Using VCO gain measurements at various frequencies, a VCO gain versus frequency curve may be obtained for each VCO.

Once the one or more VCO gain curves have been obtained, the one or more curves may be divided into a plurality of segments that may be represented by a piecewise-linear model. One or more thresholds may be calculated at block 306 to determine where to divide the one or more curves into a linear model. For example, this may include determining points on one or more curves that may be used to divide the one or more curves into substantially linear segments. One non-limiting example way to calculate the threshold is based on, among other things, determining the parasitic capacitance PAR _ CAP and the charge pump step size CP_STEP. The following equation may be used for an example threshold calculation:

in these equations, PAR _ CAP may represent the parasitic capacitance of the VCO with the maximum charge pump range, and CAP _ BITS may represent the number of capacitances, MAX (CP), used for VCO tuning_RANGE) May represent the maximum range of the total calculated charge pump range, NUM _ TH may represent the number of thresholds for dividing the VCO frequency range into segments, CP_STEPAn incremental charge pump control step per segment may be represented, and j may represent the jth threshold.

Gain adjustment model parameters may be calculated at block 308. This may include, for example, deriving a slope and intercept for each VCO gain adjustment. The slope and intercept of the curve may be obtained using any method known in the art. For purposes of illustration, a non-limiting example of an equation for calculating slope SLP and intercept OFS is provided. The following exemplary equations may be used to derive the slope SLP and intercept OFS:

in these equations, SLP [ i ]]The slope, CP, of the ith VCO gain adjustment model may be represented_RANGE[i]Can represent the charge pump range, OFS [ i ], covered between the minimum and maximum frequencies of the ith VCO]May represent the intercept or offset, KV, of the ith VCO gain adjustment model_MINCan represent the minimum VCO gain, and KV_MIN[MAX]The minimum VCO gain of the VCO with the largest charge pump range may be represented.

At block 310, the threshold and gain adjustment model parameters may be stored to memory. In some instances, these values may be stored to one or more lookup tables, such as any of the lookup tables described with reference to fig. 6. The threshold and gain adjustment model parameters may be later read from memory and used to calculate a charge pump current control value, which may be used to compensate for VCO gain variations.

Some of the previously described embodiments have provided examples relating to mobile devices. However, the principles and advantages of the embodiments may be implemented in any other system or apparatus having a need to adjust the gain of an electronic oscillator, such as a VCO. For example, any electronic device that includes a PLL may be advantageously improved by adjusting the overall loop gain of the phase locked loop as described herein.

Such a system may be implemented in various electronic systems and/or electronic devices. Examples of electronic systems may include, but are not limited to, consumer electronics, components of consumer electronics, electronic test equipment, and the like. Examples of electronic devices may include, but are not limited to, mobile phones (e.g., smart phones), telephones, televisions, computer monitors, computers, handheld computers, Personal Digital Assistants (PDAs), microwave ovens, refrigerators, automobiles, stereos, DVD recorders and/or players, CD recorders and/or players, VCRs, MP3 players, radios, camcorders, cameras (e.g., digital cameras), portable memory chips, washing machines, dryers, copiers, facsimile machines, scanners, multifunction peripherals, wristwatches, clocks, and so forth. Further, the electronic device and/or electronic system may comprise unfinished products.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, the words "include", "including", and "includes" and the like should be interpreted in the sense of "including, but not limited to". As generally used herein, the terms "coupled" or "connected" refer to two or more elements that may be connected directly or through one or more intermediate elements. Moreover, as used in this application, the words "herein," "above," "below," and words of similar import shall refer to this application as a whole and not to any particular portions of this application. Words in the above detailed description that use the singular or plural number may also include the plural or singular number, respectively, as the context permits. The word "or" when referring to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

Furthermore, unless specifically stated otherwise, or as used within the context of otherwise understood, conditional language, such as "may," "can," "might," "meeting," "etc," "e.g.," and "such as," used herein is generally intended to convey that certain embodiments include, but other embodiments do not include, certain features, elements, and/or states, among others. Thus, such conditional language is not generally intended to imply that features, elements, and/or states are in any way required for one or more embodiments or that the one or more embodiments necessarily include logic for deciding, whether or not an author inputs or prompts, whether or not such features, elements, and/or states are included or are to be performed in any particular embodiment.

The above detailed description of certain embodiments is not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the invention are described above for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. For example, while processes or blocks are presented in a given order, alternative embodiments may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified. Each of these processes or blocks may be implemented in a variety of different ways. Further, while processes or blocks are sometimes shown as occurring in series, these processes or blocks may alternatively occur in parallel, or may occur at different times.

The teachings provided herein may be applied to other systems, not necessarily the systems described above. Elements and acts of the various embodiments described above can be combined to provide further embodiments.

While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the present disclosure. Indeed, the novel methods and systems described herein may be embodied in various other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure.

Claims (22)

1. A method for compensating for variations in a Voltage Controlled Oscillator (VCO) gain, the method comprising:

selecting a VCO gain adjustment model based on the VCO gain indicator;

obtaining VCO gain adjustment model parameters from a memory;

calculating a charge pump control value using the VCO gain adjustment model parameters; and

dynamically compensating for VCO gain variations using the charge pump control value.

2. The method of claim 1 wherein the VCO gain indicator is indicative of a VCO output frequency.

3. The method of claim 1 wherein the VCO gain indicator is indicative of a capacitance value in a tunable capacitance circuit configured to control a frequency of a VCO output.

4. The method of claim 3, wherein selecting the gain adjustment model comprises comparing the capacitance value to a threshold value.

5. The method of claim 1, wherein the gain adjustment parameters include a slope and an offset.

6. The method of claim 1 wherein obtaining VCO gain adjustment model parameters is based on a VCO selected from a plurality of VCOs.

7. The method of claim 1 further comprising calculating the VCO gain model parameters and storing the VCO gain model parameters to the memory.

8. An apparatus comprising a charge pump controller, the charge pump current controller comprising:

a memory configured to store VCO gain model parameters and thresholds; and

an arithmetic logic unit configured to select a VCO gain model based on a comparison of a VCO gain indicator to at least one threshold value stored in the memory; obtaining VCO gain model parameters corresponding to the selected VCO gain model from the memory; and calculating a charge pump control value using the VCO gain model parameters.

9. The apparatus of claim 8, wherein the VCO gain indicator is indicative of a VCO output frequency.

10. The apparatus of claim 8 wherein the VCO gain indicator is indicative of a capacitance value in a circuit configured to control a VCO output frequency, and wherein the threshold values stored in the memory represent threshold capacitance values.

11. The apparatus of claim 8 wherein the VCO gain model parameters correspond to a plurality of VCOs.

12. The apparatus of claim 11, wherein the arithmetic logic unit is further configured to obtain VCO gain model parameters corresponding to a selected one of the plurality of VCOs.

13. The apparatus of claim 8 wherein the VCO gain model parameters stored in the memory comprise at least a slope and an offset.

14. The apparatus of claim 8, wherein the apparatus further comprises a VCO.

15. The apparatus of claim 14, wherein the arithmetic logic unit is further configured to dynamically cause adjustment of a gain of the VCO based on the charge pump control value.

16. The apparatus of claim 8, wherein the VCO gain model represents a portion of a VCO correction curve representing the VCO output frequency indicator versus the charge pump current control value.

17. The apparatus of claim 8, further comprising a phase locked loop comprising a VCO and a charge pump, the charge pump configured to receive the charge pump current control value from the charge pump controller, and the charge pump further configured to adjust a gain of the VCO based on the charge pump current control value.

18. The apparatus of claim 8 wherein the charge pump controller is further configured to calculate the VCO gain model parameters and the at least one threshold value and store the VCO gain model parameters and the at least one threshold value to memory.

19. The apparatus of claim 18 wherein the charge pump controller is configured to calculate the VCO gain model parameters in response to detecting a calibration event.

20. The apparatus of claim 8 wherein the memory comprises at least one lookup table configured to store at least one of the threshold values and the VCO gain model parameters.

21. An apparatus, comprising:

means for selecting a VCO gain model based on a comparison of the VCO gain indicator to at least one threshold value stored in memory;

means for obtaining VCO gain model parameters corresponding to the selected VCO gain model from the memory; and

means for calculating a charge pump current control value using the VCO gain model parameters.

22. The apparatus of claim 21, configured as a base station.