CN106936429A - Local oscillator and local oscillated signal production method - Google Patents

Abstract

The invention provides a local oscillator and a method for generating a local oscillator signal. The output terminal of the voltage controlled oscillator is connected to the input terminal of the RC-CR phase-shift network, and the output terminals of the two RC-CR phase-shift networks are connected to the first branch The input end of the frequency division circuit, the input end of the second frequency division circuit, and the first input end of the image rejection mixer are connected, and the output end of the first frequency division circuit or the output end of the second frequency division circuit is connected with the image rejection mixer The second input terminal of the image rejection mixer is connected to the input terminal of the third frequency dividing circuit. The local oscillation signal is generated by first generating the quadrature signal and then performing the mixing process. Compared with the generation of the local oscillation signal by first performing the frequency mixing process and then generating the quadrature signal, the output of the image suppression mixer in the present invention is The frequency of the signal is different from that of the local oscillation signal, which increases the frequency of the output signal of the image rejection mixer, thereby reducing the chip area occupied by the inductor and effectively reducing the production cost.

Description

Local oscillator and local oscillator signal generation method

technical field

The invention relates to the technical field of electronic communication, in particular to a local oscillator and a method for generating a local oscillator signal.

Background technique

A Voltage Controlled Oscillator (VCO) is used as an initial frequency signal source for a Local Oscillator (LO) to transmit and/or receive information over a wireless or wired channel. Due to the high transmission frequency of VCOs, it is difficult to generate "pure" high-frequency signals. Noise on the LO can mix with blocker signals to desensitize the receiver. This is even more of a challenge when implementing various transceivers supporting different frequency bands in a single chip. For example, the LO's unwanted spectral tones can interfere with another transceiver's receiver section.

Existing methods for generating an LO signal mainly include an image rejection mixing method. As shown in FIG. 1 , it is a schematic structural diagram of an existing local oscillator. The local oscillator adopts an image-reject mixing scheme, and the local oscillator includes: a voltage-controlled oscillator (VCO), three buffers, an image-reject mixer, three divide-by-2 circuits, and two RC-CRs The phase shift network, the voltage controlled oscillator generates a signal with a frequency of Wc, the signal with a frequency of Wc is processed by two buffers and transmitted to a divide-by-2 circuit to generate a signal with a frequency of 0.5Wc, and the two signals input by the image rejection mixer The quadrature signal of the frequency component is generated by the output of two divide-by-2 circuits, the frequencies are 0.5Wc and 0.25Wc respectively, after passing through the image rejection mixer, a signal with a frequency of 0.75Wc is generated, and then passed through the remaining buffer and then through the RC -CR produces four quadrature signals (IQ) with the same frequency of 0.75Wc. However, since the final quadrature signals and the output of the image rejection mixer are all at a frequency of 0.75Wc, if the frequency is not very high (such as 0.75Wc=2.4GHz), according to the inductor-capacitor resonance formula: It can be seen that the currently required inductance value will be relatively large, resulting in the inductance occupying a large chip area and increasing the production cost.

Contents of the invention

The purpose of the present invention is to provide a local oscillator and a local oscillator signal generation method to solve the problem of using the existing local oscillator using the image rejection mixing scheme, which requires a large inductance value, causing the inductance to occupy a large chip area. Increased production costs.

In order to solve the above technical problems, the present invention provides a local oscillator, which includes: a voltage controlled oscillator, two RC-CR phase shift networks, a first frequency division circuit, a second frequency division circuit , a third frequency division circuit and an image rejection mixer; the output terminal of the voltage controlled oscillator is connected with the input terminal of the RC-CR phase shift network, and the output of the two RC-CR phase shift networks The terminal is connected with the input terminal of the first frequency division circuit, the input terminal of the second frequency division circuit, and the first input terminal of the image rejection mixer, and the output terminal of the first frequency division circuit or the The output terminal of the second frequency division circuit is connected to the second input terminal of the image rejection mixer, and the output terminal of the image rejection mixer is connected to the input terminal of the third frequency division circuit.

Optionally, the local oscillator further includes a first buffer unit, a second buffer unit and a third buffer unit, the input end of the first buffer unit is connected to the output end of the voltage-controlled oscillator , the output of the first buffer unit is connected to the input of the two RC-CR phase shift networks; the input of the second buffer unit is connected to the output of the two RC-CR phase shift networks , the output end of the second buffer unit is connected to the input end of the first frequency division circuit and the input end of the second frequency division circuit; the input end of the third buffer unit is mixed with the image rejection The output end of the device is connected, and the output end of the third buffer unit is connected with the input end of the third frequency dividing circuit.

Optionally, the local oscillator further includes a correction resistor, and the correction resistor is connected in parallel to both ends of the resistor in the RC-CR phase shift network through switch control.

Optionally, in the local oscillator, the number of the correction resistors is two groups, and each group of correction resistors is connected in parallel to two resistors of a resistor in the RC-CR phase shift network through a switch control mode of several bit widths. end.

Optionally, in the local oscillator, the first frequency division circuit, the second frequency division circuit and the third frequency division circuit are divide-by-2 circuits.

Optionally, in the local oscillator, the voltage-controlled oscillator generates a signal of the first frequency.

Optionally, in the local oscillator, the signals input to the image rejection mixer include four quadrature signals of the first frequency and four quadrature signals of the second frequency, and the third frequency division The output signal of the circuit is a local oscillation signal, and the first frequency is twice the second frequency.

Optionally, in the local oscillator, the signal frequency of the signal output by the image rejection mixer is 1.5 times the first frequency, and the signal frequency of the local oscillator signal is 0.75 times the first frequency.

The present invention also provides a method for generating a local oscillating signal. The method for generating a local oscillating signal uses the above-mentioned local oscillator for generation.

Optionally, in the local oscillation signal generation method, including:

The oscillation frequency of the voltage-controlled oscillator is set according to the frequency of the local oscillation signal to be generated. When the first frequency division circuit, the second frequency division circuit and the third frequency division circuit are all divided by 2 circuits, the The frequency of the local oscillation signal to be generated is 0.75 times the oscillation frequency of the voltage-controlled oscillator.

In the local oscillator and local oscillation signal generation method provided by the present invention, the output terminal of the voltage controlled oscillator is connected to the input terminal of the RC-CR phase shift network, and the output terminals of the two RC-CR phase shift networks are connected to the first The input end of the frequency division circuit, the input end of the second frequency division circuit, and the first input end of the image rejection mixer are connected, and the output end of the first frequency division circuit or the output end of the second frequency division circuit is mixed with the image rejection The second input end of the mixer is connected, and the output end of the image rejection mixer is connected with the input end of the third frequency division circuit. The local oscillation signal is generated by first generating the quadrature signal and then performing the mixing process. Compared with the generation of the local oscillation signal by first performing the frequency mixing process and then generating the quadrature signal, the output of the image suppression mixer in the present invention is The frequency of the signal is different from that of the local oscillation signal, which increases the frequency of the output signal of the image rejection mixer, thereby reducing the chip area occupied by the inductor and effectively reducing the production cost.

Description of drawings

FIG. 1 is a schematic structural diagram of an existing local oscillator;

FIG. 2 is a schematic structural diagram of a local oscillator in an embodiment of the present invention;

Fig. 3 a is the response curve of the magnitude and frequency of RC-CR phase-shifting network in an embodiment of the present invention;

Fig. 3 b is the response curve of the phase and frequency of RC-CR phase-shifting network in one embodiment of the present invention;

Fig. 4 is a schematic diagram of the RC-CR phase shift network after adding a correction resistor in an embodiment of the present invention;

Figure 5 is a schematic diagram of an image reject mixer;

Figure 6 is a circuit diagram of an image reject mixer.

detailed description

The local oscillator and the local oscillator signal generation method proposed by the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. Advantages and features of the present invention will be apparent from the following description and claims. It should be noted that all the drawings are in a very simplified form and use imprecise scales, and are only used to facilitate and clearly assist the purpose of illustrating the embodiments of the present invention.

Please refer to FIG. 2, which is a schematic structural diagram of a local oscillator in this embodiment. As shown in FIG. 2, the local oscillator includes: a voltage-controlled oscillator (VCO), two RC-CR phase-shifting networks (also RC-CR network), a first frequency division circuit, a second frequency division circuit, a third frequency division circuit and an image rejection mixer; the output terminal of the voltage controlled oscillator is connected to the RC-CR The input terminals of the phase shift network are connected, the output terminals of the two RC-CR phase shift networks are connected with the input terminals of the first frequency division circuit, the input terminals of the second frequency division circuit, the image rejection mixing The first input end of the device is connected, the output end of the first frequency division circuit or the output end of the second frequency division circuit is connected with the second input end of the image rejection mixer, and the image rejection mixer The output terminal of the device is connected with the input terminal of the third frequency dividing circuit. Preferably, the first frequency division circuit, the second frequency division circuit and the third frequency division circuit are divide-by-2 circuits. Preferably, the first frequency division circuit, the second frequency division circuit, and the third frequency division circuit include, but are not limited to, a divide-by-2 circuit, and may also be a divide-by-4 circuit or a divide-by-6 circuit.

Further, the local oscillator further includes a first buffer unit, a second buffer unit and a third buffer unit, the input end of the first buffer unit is connected to the output end of the voltage-controlled oscillator, and the first buffer unit The output end of the described two RC-CR phase-shift networks is connected; the input end of the second buffer unit is connected with the output ends of the two RC-CR phase-shift networks, and the second buffer unit The output end of the first frequency division circuit is connected to the input end of the second frequency division circuit; the input end of the third buffer unit is connected to the output end of the image rejection mixer, so The output terminal of the third buffer unit is connected to the input terminal of the third frequency division circuit.

Specifically, as shown in FIG. 2, the first buffer unit includes two buffers, the input end of each buffer is connected to the output end of the voltage-controlled oscillator, and the output end of each buffer is connected to an RC- The input terminal of the CR network is connected to initially shape the waveform of the signal output by the voltage-controlled oscillator; the second buffer unit includes four buffers, and each RC-CR network includes a CR circuit and an RC circuit, and each RC -The output terminals of the CR circuit and the RC circuit in the CR network are correspondingly connected to a buffer to shape the waveform of each output signal, further improve the quality of the output signal, and improve the anti-interference ability of the output signal; the third buffer The unit includes a buffer for waveform shaping the signal output from the image reject mixer. In summary, the output of each device will follow the design of a buffer, so that the quality of the signal processed by each device is the best, improve the quality of the signal waveform and improve its anti-interference ability to ensure the final The quality of the resulting local oscillator signal.

In order to better understand the image rejection mixer, the following will be described in detail in conjunction with FIG. 5 and FIG. 6 .

Please refer to FIG. 5 , which is a schematic diagram of the image reject mixer in this embodiment. The principle shown in Figure 5 can be characterized by the following formula:

sin(Wa*t)*cos(Wb*t)=0.5(sin(Wa+Wb)*t+sin(Wa-Wb)*t);

cos(Wa*t)*sin(Wb*t)=0.5(sin(Wa+Wb)*t-sin(Wa-Wb)*t);

sin(Wa*t)*cos(Wb*t)+cos(Wa*t)*sin(Wb*t)=sin(Wa+Wb)*t.

Among them, Wa and Wb are frequencies with different values.

Please refer to FIG. 6 , which is a circuit diagram of the image reject mixer in this embodiment. In Fig. 6, Ibias is a current source, M1-M4 are transconductors, M1-M4 are connected to a quadrature signal whose frequency is Wb (corresponding to the signal frequency input by the first input terminal of the image rejection mixer), and M5-M12 are switches Tubes, wherein M5-M8 are connected to the I-channel differential signal with a frequency of Wa (corresponding to the signal frequency input from the second input terminal of the image rejection mixer), and M9-M12 are connected to the Q-channel differential signal with a frequency of Wb. The inductor L and the capacitor C resonate at the frequency (Wa+Wb), so OUTN and OUTP are differential signals with the frequency (Wa+Wb).

Please continue to refer to FIG. 2, FIG. 5 and FIG. 6. In this embodiment, the voltage-controlled oscillator (VCO) oscillates at the Wc frequency, and Wc can be set according to actual needs. The differential oscillation signal output by the voltage-controlled oscillator passes through the first One buffer unit is sent to two RC-CR phase-shifting networks, and the two RC-CR phase-shifting networks generate four quadrature signals with a frequency of Wc, and these four quadrature signals with a frequency of Wc respectively pass through a corresponding buffer , output 4 differential signals with a frequency of Wc, and send the I differential signal (corresponding to the signals cos(Wc*t) and -cos(Wc*t) in Figure 2) to the first divide-by-2 circuit to generate a positive signal with a frequency of 0.5Wc The cross signal (ie cos(0.5Wc*t), -cos(0.5Wc*t)) is sent to the first input terminal of the image rejection mixer, and the Q-way differential signal (corresponding to the signal in Figure 2 sin(Wc*t) and -sin(Wc*t)) are sent to the second divide-by-2 circuit to generate a quadrature signal of 0.5Wc frequency (ie sin(0.5Wc*t), -sin(0.5Wc*t)) and Send it to the first input of the image rejection mixer to balance the load of the I and Q channels. The signal input by the second input terminal of the image rejection mixer is an orthogonal signal whose frequency is Wc after the output signals of two RC-CR phase-shifting networks have undergone waveform shaping (corresponding to the middle signal sin(Wc*t), -sin (Wc*t), cos(Wc*t) and -cos(Wc*t). The two frequency components input to the image rejection mixer through the first input terminal and the second input terminal are respectively the positive values of 0.5Wc and Wc The quadrature signal is mixed to generate a differential signal with a frequency of 1.5Wc, and then sent to the third division by 2 circuit after passing through the third buffer unit to generate a quadrature local oscillation signal with a well-matched amplitude and phase at a frequency of 0.75Wc (corresponding to the figure 2 in I_P, I_N, Q_P, Q_N).

Compared with the existing local oscillator structure shown in Figure 1, the local oscillator structure shown in Figure 2 has changes in the position of the RC-CR phase-shift network settings. Based on this change, the settings of the corresponding subsequent devices and line connections are all Something has changed. In Figure 1, the two frequency components input to the image rejection mixer are 0.5Wc and 0.25Wc respectively, and the output signal of the image rejection mixer is a differential signal with a frequency of 0.75Wc; while in Figure 2, due to the front of the RC-CR network Set so that the two frequency components input to the image reject mixer are 0.5Wc and Wc respectively, and the image reject mixer outputs a differential signal with a frequency of 1.5Wc. According to the inductor-capacitor resonance formula: Calculation, since the output signal frequency (0.75Wc) of the image rejection mixer in Figure 1 is halved compared to the output signal frequency (1.5Wc) of the image rejection mixer in Figure 2, the inductance value required for Figure 1 is required for Figure 2 4 times of the inductance value, so the inductance area in the scheme in Fig. 1 is greatly reduced compared with the inductance area in the scheme in Fig. 2 . For the first frequency division circuit, the second frequency division circuit and the third frequency division circuit are divided by 4 circuits and are all divided by 2 circuits, it is the same. Specifically, you can refer to the elaboration content in Figure 2, which can also reduce The area of the inductor will not be described in detail here.

Aiming at the shortcomings of the RC-CR network, the preferred solution of the present invention has been further improved, as follows:

Please refer to Figure 3a, the curve marked with |H _HPF | is the response curve corresponding to the amplitude (A) and frequency (ω) of the CR circuit; the curve marked with |H _LPF | is the response curve corresponding to the amplitude and frequency of the RC circuit .

Please refer to Figure 3b, the curve marked with ∠H _HPF is the response curve corresponding to the phase (ψ) and frequency (ω) of the CR circuit; the curve marked with ∠H _LPF is the response curve corresponding to the phase and frequency of the RC circuit.

It can be seen from the curve in Figure 3b that the signals output by the CR circuit and the RC circuit have a phase difference of 90 degrees at any frequency It can be seen from the curve in Fig. 3a that only at the frequency ω=1/(R1*C1), the amplitudes of the signals output by the CR circuit and the RC circuit are equal, and there is a mismatch between the amplitudes of the signals output by the CR circuit and the RC circuit at other frequencies.

In view of the above-mentioned problems, in order to overcome the influence of resistance or capacitance mismatch on the amplitude mismatch of the output signal, the present invention connects the two ends of the resistance R in the RC-CR phase shift network in the local oscillator in parallel with the correction resistance R1 through switch control Compensate in a way to solve it. Please refer to FIG. 4 for the specific solution. There are two sets of correction resistors, and each set of correction resistors is connected in parallel to both ends of a resistor in the RC-CR phase-shift network by means of switches with several bit widths. Specifically, a set of correction resistors R1 is connected in parallel to both ends of the resistor R in the CR circuit through switch control, and another set of correction resistors R1 is connected in parallel to both ends of the resistor R in the RC circuit through switch control. When matching, an appropriate correction resistor R1 is selected to be connected in parallel to both ends of a resistor in the CR circuit and the RC circuit, so as to reduce the influence of the mismatch of resistance or capacitance on the amplitude mismatch of the output signal.

Correspondingly, this embodiment also provides a method for generating a local oscillation signal. The method for generating a local oscillation signal in this embodiment will be described in detail below with reference to FIG. 2 .

In the local oscillation signal generation method, it is first necessary to set the oscillation frequency of the voltage-controlled oscillator according to the frequency of the local oscillation signal to be generated. It has been verified that the first frequency division circuit, the second frequency division circuit and the third frequency division circuit When the frequency dividing circuits are divide-by-2 circuits, the frequency of the local oscillation signal to be generated is 0.75 times the oscillation frequency of the voltage-controlled oscillator. The principle of setting the oscillation frequency of the voltage-controlled oscillator can be verified according to the following example.

In order to better understand the generation process of the local oscillating signal of the present invention, below in conjunction with Fig. 2, taking the local oscillating signal with a frequency of 2.4GHz (that is, 0.75Wc=2.4GHz) as an example, at this time Wc=3.2GHz, therefore, the VCO It needs to oscillate on 3.2GHz, and generate 4 orthogonal signals after passing through two RC-CR networks, which are: Cos(2pi*3.2*10^9*t), -Cos(2pi*3.2*10^9*t ), Sin(2pi*3.2*10^9*t), -Sin(2pi*3.2*10^9*t); where Cos(2pi*3.2*10^9*t) and -Cos(2pi*3.2* The differential signal of 10^9*t) is generated by a divide-by-2 circuit Cos(2pi*1.6*10^9*t), -Cos(2pi*1.6*10^9*t), Sin(2pi*1.6*10^ 9*t) and -Sin(2pi*1.6*10^9*t); the other differential signal Sin(2pi*3.2*10^9*t), -Sin(2pi*3.2*10^9*t) is the same Connect an identical divide-by-2 circuit to balance the load.

Quadrature signal Cos(2pi*3.2*10^9*t), -Cos(2pi*3.2*10^9*t), Sin(2pi*3.2*10^9*t), -Sin(2pi*3.2* 10^9*t) to the first input of the image reject mixer, Cos(2pi*1.6*10^9*t), -Cos(2pi*1.6*10^9*t), Sin(2pi *1.6*10^9*t) and -Sin(2pi*1.6*10^9*t) are sent to the second input terminal of the image rejection mixer, and Sin(2pi* 4.8*10^9*t) and -Sin(2pi*4.8*10^9*t) oscillating signals, and then sent to a divide-by-2 circuit after passing through the buffer to obtain Cos(2pi*2.4*10^9*t) , -Cos(2pi*2.4*10^9*t), Sin(2pi*2.4*10^9*t), -Sin(2pi*2.4*10^9*t) quadrature local oscillator signal.

In summary, in the local oscillator and local oscillation signal generation method provided by the present invention, the output terminal of the voltage controlled oscillator is connected to the input terminal of the RC-CR phase-shift network, and the output terminals of the two RC-CR phase-shift networks Connect with the input terminal of the first frequency division circuit, the input terminal of the second frequency division circuit, the first input terminal of the image rejection mixer, the output terminal of the first frequency division circuit or the output terminal of the second frequency division circuit and the mirror image The second input terminal of the rejection mixer is connected, and the output terminal of the image rejection mixer is connected with the input terminal of the third frequency dividing circuit. The local oscillation signal is generated by first generating the quadrature signal and then performing the mixing process. Compared with the generation of the local oscillation signal by first performing the frequency mixing process and then generating the quadrature signal, the output of the image suppression mixer in the present invention is The frequency of the signal is different from that of the local oscillation signal, which increases the frequency of the output signal of the image rejection mixer, thereby reducing the chip area occupied by the inductor and effectively reducing the production cost.

The above description is only a description of the preferred embodiments of the present invention, and does not limit the scope of the present invention. Any changes and modifications made by those of ordinary skill in the field of the present invention based on the above disclosures shall fall within the protection scope of the claims.

Claims (10)

1. a kind of local oscillator, it is characterised in that including：One voltage controlled oscillator, two RC-CR phase-shift networks, one first point Frequency circuit, one second frequency dividing circuit, a Divide-by-3 circuit and an image-reject mixer；The output end of the voltage controlled oscillator Input with the RC-CR phase-shift networks is connected, and the output end of described two RC-CR phase-shift networks and the described first frequency dividing are electric The input on road, the input of second frequency dividing circuit, the first input end connection of the image-reject mixer, described the The output end of the output end of one frequency dividing circuit or second frequency dividing circuit and the second input of the image-reject mixer Connection, the output end of the image-reject mixer is connected with the input of the Divide-by-3 circuit.

2. local oscillator as claimed in claim 1, it is characterised in that also including the first buffer cell, the second buffer cell And the 3rd buffer cell, the input of first buffer cell is connected with the output end of the voltage controlled oscillator, and described first The output end of buffer cell is connected with the input of described two RC-CR phase-shift networks；The input of second buffer cell Output end with described two RC-CR phase-shift networks is connected, and the output end of second buffer cell and the described first frequency dividing are electric The input connection of the input on road, second frequency dividing circuit；The input of the 3rd buffer cell presses down with the mirror image The output end connection of frequency mixer processed, the output end of the 3rd buffer cell is connected with the input of the Divide-by-3 circuit.

3. local oscillator as claimed in claim 1, it is characterised in that also including correction resistance, the correction resistance passes through The mode for switching control is parallel to the two ends of resistance in RC-CR phase-shift networks.

4. local oscillator as claimed in claim 3, it is characterised in that the quantity of the correction resistance is two groups, every group of school Positive resistance some bit wides switch control by way of be parallel to RC-CR phase-shift networks in a two ends for resistance.

5. local oscillator as claimed in claim 1, it is characterised in that first frequency dividing circuit, the second frequency dividing electricity Road and the Divide-by-3 circuit are except 2 circuits.

6. local oscillator as claimed in claim 5, it is characterised in that the voltage controlled oscillator generates the letter of first frequency Number.

7. local oscillator as claimed in claim 6, it is characterised in that the signal of the input image-reject mixer includes The orthogonal signalling of the orthogonal signalling of four road first frequencies and four road second frequencies, the output signal of the Divide-by-3 circuit is this Ground oscillator signal, the first frequency is two times of the second frequency.

8. local oscillator as claimed in claim 7, it is characterised in that the letter of the signal of the image-reject mixer output Number frequency is 1.5 times of first frequency, and the signal frequency of the local oscillated signal is 0.75 times of first frequency.

9. a kind of production method of local oscillated signal, it is characterised in that using as any one of claim 1~8 Local oscillator is produced.

10. local oscillated signal production method as claimed in claim 9, including：

The frequency of oscillation of the frequency setting voltage controlled oscillator according to the local oscillated signal to be produced, first frequency dividing circuit, Second frequency dividing circuit and the Divide-by-3 circuit are during except 2 circuit, the frequency of the local oscillated signal to be produced It is 0.75 times of the frequency of oscillation of voltage controlled oscillator.