CN1119870C - Adaptive digital jitter signal control method and MF emitter in the said method - Google Patents

Abstract

The invention provides an adaptive digital jitter signal control method and an intermediate frequency transmitter. The disadvantage of the traditional method is that the provided Dither signal is constant throughout the process and cannot adapt to changes in the environment and input signals. The method provided by the present invention adds a feedback branch on the basis of the traditional method, that is, analog-to-digital conversion is performed on the analog input signal to generate a feedback digital input signal; the feedback digital input signal is compared with the mixed input signal to generate a control signal; The control signal is used to control the generation of the digital jitter signal. The invention also provides an intermediate frequency transmitter using the control method.

Description

Adaptive digital jitter signal control method and intermediate frequency transmitter using the method

technical field

The present invention relates to telecommunication technology, in particular to a method for controlling an adaptive digital dither signal and a digital intermediate frequency transmitter using the method for controlling the adaptive digital dither signal.

Background technique

The digitalization brought about by the rapid development of large-scale integrated circuits (VLSI) is a main feature of today's intensified information technology. It is reflected in radio communication equipment that digital devices are getting closer and closer to antennas. The benefits of this trend It is easy to produce, low in cost, more in function and better in performance.

In the IF transmitter of such a wireless system, the digital up-converter (DUC) and the digital-to-analog converter (DAC) are two key functional components. They up-convert the baseband processed and digitally modulated signal, and then convert the digital intermediate frequency signal into an analog intermediate frequency signal through a digital-to-analog converter, and then send it to the subsequent radio frequency module. The performance index of the digital-to-analog converter (mainly referring to the signal-to-noise ratio SNR and the false-free dynamic range SFDR) is the first level to determine the quality of the radio frequency signal transmitted from the antenna port. Among them, the SFDR index is the most difficult to meet.

For the improvement of the non-false dynamic range index of the digital-to-analog converter, in addition to using chips with better performance indicators and providing high-precision clocks, an eye-catching method is to add a dither signal (Dither Signal) to the useful signal. , the principle is: in the analog-to-digital converter, its non-linear characteristics have certain regularity. It is reflected in the frequency spectrum that some harmonics and spurious points are relatively high. By adding the Dither signal, the above regularity can be broken, and the spurs in the output of the digital-to-analog converter can be suppressed to the noise floor, thereby improving the nonlinear characteristics of the system and improving the SFDR index of the system. Dither signals include wideband Dither and narrowband Dither. Among them, the narrowband Dither is used more.

In common dither applications, the general method is to find the best dither signal through experiments, and solidify each parameter in the circuit and design. This approach has some problems:

1. For different digital-to-analog conversion circuits and chips, the corresponding optimal Dither signal is different. Then there are certain differences in circuit and design. This means that the versatility of the circuit is not good, and the Dither circuit and design used in a certain digital-to-analog circuit cannot be completely copied to another digital-to-analog conversion circuit.

2. For the same type of digital-to-analog conversion chips and circuits, there are certain differences between different individuals, which cannot be reflected in this solidified Dither design.

3. As the environment changes (such as temperature, etc.), the performance of the digital-to-analog conversion circuit and the chip will also change accordingly, and the solidified Dither design cannot adapt to this change.

4. The effect of Dither has a certain relationship with the input signal, and the solidified Dither signal cannot track the slow change of the input signal.

The above-mentioned factors are not considered in the traditional method, on the one hand, because the original system does not have very high requirements on linearity, and on the other hand, it is not easy to change the Dither signal in real time. In modern wireless systems, the linearity of the entire channel is highly required, and the linearity of the digital-to-analog converter plays a considerable role. Therefore, the above factors need to be considered.

Contents of the invention

Therefore, the object of the present invention is to provide a control method of adaptive digital dithering signal, which can adaptively adjust the digital dithering signal generated according to different digital-to-analog conversion circuits, environments and input signals, so as to provide the best digital dithering signal. Jitter signal.

Another object of the present invention is to provide a digital intermediate frequency transmitter using the above-mentioned adaptive digital jitter signal control method. Controlled digital dithering signal in order to provide the best digital dithering signal for the digital-to-analog conversion circuit.

According to the above-mentioned purpose, the control method of the self-adaptive digital jitter signal provided by the present invention comprises the following steps:

a. Generate an initial digital jitter signal;

b. up-converting and mixing the digital dithering signal with the input signal to generate an intermediate frequency mixed input signal;

c. Perform digital-to-analog conversion on the intermediate frequency mixed input signal to generate an analog mixed input signal;

d. Perform intermediate frequency filtering on the analog mixed input signal, filter out the out-of-band signal, and generate an analog input signal;

e. Perform analog-to-digital conversion on the analog input signal to generate a feedback digital input signal;

f. performing spectrum estimation on the feedback digital input signal and the above-mentioned intermediate frequency mixed input signal to generate a control signal;

g. Use the control signal to control the generation of the digital dithering signal; then return to step b, and so on.

According to another object of the present invention, the digital intermediate frequency transmitter provided by the present invention includes:

a baseband unit for providing digital input signals;

A jitter signal generator for providing a jitter signal;

The up-converter is used for up-converting the digital input signal provided by the baseband unit to generate an intermediate frequency digital input signal;

a mixer for mixing the jitter signal provided by the jitter signal generator with the intermediate frequency digital input signal generated by the up-converter to generate an intermediate frequency mixed input signal;

The digital-to-analog converter performs digital-to-analog conversion on the mixed intermediate frequency mixed input signal to generate an analog mixed input signal;

An intermediate frequency filter, connected to the digital-to-analog converter, filters out the intermediate frequency signal in the analog mixed input signal to generate an analog input signal;

a radio frequency unit, receiving the analog input signal generated by the intermediate frequency filter, and performing radio frequency processing,

The digital intermediate frequency transmitter also includes a feedback branch, and the feedback branch includes:

An analog-to-digital converter, connected to the intermediate frequency filter, performs analog-to-digital conversion on the analog input signal generated by the intermediate frequency filter to generate a feedback digital input signal;

an adaptive controller, connected to the output of the up-converter and the output of the analog-to-digital converter, for mixing the input signal according to the feedback digital input signal generated by the analog-to-digital converter and the intermediate frequency generated by the mixer Spectrum estimation is performed to generate a control signal, which is input into the dithering signal generator for controlling the dithering signal generator to generate a dithering signal.

Description of drawings

Fig. 1 is the flow chart of adaptive digital dithering signal generation method of the present invention;

Fig. 2 is the constitution block diagram of digital intermediate frequency transmitter of the present invention;

Figure 3 is an example of the adaptive controller 90 in Figure 2;

FIG. 4 is a further circuit block diagram of the up-converter, the Dither signal generator and the mixer in FIG. 2 .

Detailed ways

Embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

Fig. 1 is a flowchart of the adaptive digital dithering signal control method of the present invention. The flow of the method of the present invention will be described below first according to the flow chart. As shown in Figure 1, the initial Dither signal is first generated in a traditional way (step S1); then, in step S2, the initial Dither signal is up-converted and mixed with the input signal from the front-end baseband unit to obtain an intermediate frequency mixed input signal . As in the traditional method, the intermediate frequency mixed signal is converted into an analog mixed input signal through digital-to-analog conversion (step S3). These steps are the same as the traditional method of adding a Dither signal to the input signal to improve the SFDR index of the digital-to-analog converter. Then, after step S3, the analog mixed input signal is provided to an intermediate frequency filter for filtering to obtain an analog input signal (step S4). In a traditional method, the analog input signal is provided to a subsequent radio frequency unit for transmission.

As mentioned earlier, the disadvantage of this traditional method is that the initially provided Dither signal remains unchanged throughout the process, and cannot adapt to changes in the environment and input signals, and cannot optimally improve the SFDR of the digital-to-analog converter. index.

The characteristic point of the present invention is, when the analog input signal after the intermediate frequency filtering of step S4 is provided to the radio frequency unit of subsequent stage, also this analog input signal is taken out, carries out analog-to-digital conversion, obtains the feedback digital input signal (step S5) . Then, compare the feedback digital input signal with the intermediate frequency mixed input signal output in step S2 to generate a control signal (step S6). Finally, in step S7, the control signal is used to control the generation of the Dither signal input to the up-converter, or in other words, to adjust the generation of the Dither signal.

From the above method of the present invention, the present invention adds a feedback step on the basis of the original method, and adjusts the parameters of the Dither signal adaptively according to the feedback signal, so that the generated Dither signal can best adapt to the data. analog converters as well as environmental changes and changes in the input signal.

The main flow of the method for controlling the adaptive digital Dither signal of the present invention is described above. The digital intermediate frequency transmitter using the above-mentioned adaptive digital Dither signal control method of the present invention will be described below with reference to FIG. 2 .

Fig. 2 is a structural block diagram of the digital intermediate frequency transmitter of the present invention. As shown in FIG. 2 , a traditional digital IF transmitter mainly includes a baseband unit 10 , a Dither signal generator 20 , an upconverter 30 , a mixer 40 , a digital-to-analog converter 50 , an IF filter 60 and a radio frequency unit 70 . The baseband unit 10 provides an input signal, and the up-converter 30 up-converts the input signal into an intermediate frequency input signal. In the mixer 40, the intermediate frequency input signal output by the up-converter 20 is mixed with the Dither signal generated by the Dither signal generator 20, and an intermediate frequency mixed input signal is output. The digital-to-analog converter 50 performs digital-to-analog conversion on the intermediate frequency mixed input signal to generate an analog mixed input signal. The intermediate frequency filter 60 filters the analog mixed input signal output by the digital-to-analog converter 50 to filter out out-of-band signals and also filter out the Dither signal mixed into the input signal in the mixer 40 . An intermediate frequency transmitter with a traditional structure provides the analog input signal output by the intermediate frequency filter 60 to the radio frequency unit 70 for radio frequency processing.

The problem that the digital intermediate frequency transmitter of this traditional structure exists is the same as the traditional method described above, that is, the Dither signal provided by the Dither signal generator 20 is constant throughout the process, and cannot adapt to changes in the environment and changes in the input signal. The SFDR index of the digital-to-analog converter 30 cannot be improved optimally.

Corresponding to the above method, the IF transmitter of the present invention is characterized in that, as shown in FIG. 2 , an analog-to-digital converter 80 and an adaptive controller 90 are added. The output signal of the intermediate frequency filter 60 is divided into one channel and provided to the analog-to-digital converter 80 . The analog-to-digital converter 80 converts the analog input signal into a digital signal again, and provides it to the adaptive controller 90 as a feedback digital input signal. The adaptive controller 90 has two input terminals, one input terminal is used to receive the feedback digital input signal output by the analog-to-digital converter 80; the other input terminal is used to be connected with the output of the mixer 40, and is used to receive the output of the mixer 40 The IF mixed input signal (the signal includes the Dither signal). Then, the adaptive controller 90 compares the feedback digital input signal with the intermediate frequency mixed input signal to generate a control signal, and provides the control signal to the Dither signal generator 20 for controlling the Dither signal generated by the Dither signal generator 20, In order to gradually generate the best Dither signal suitable for the digital-to-analog converter 50 .

In the above example, the Dither signal generator 20 and the up-converter 30 are provided separately. However, it should be understood that in some other embodiments, these two components can also be combined together. FIG. 4 shows a functional block diagram of an up-converter with the function of generating an up-Dither signal.

As shown in FIG. 4 , the upper part in FIG. 4 is actually a Dither signal generating circuit, which includes: a random number generator 201 for generating a random number signal. In a practical example, it can be an m-sequence generator, or any other random number sequence generator; coefficient storage finite impulse response filter (Finite Impulse response) 202; cascaded integral comb interpolation filter 203, the filter can change the lower rate digital signal into a higher rate digital signal with less resources and acceptable performance, and the filter 203 can also use multiple cascaded integrating comb filter stages The way that connects, to increase the flexibility of application; Numerical control oscillator 205, is used to produce the digital intermediate frequency oscillating signal of complex number (two-way quadrature); The signal is multiplied by the complex digital intermediate frequency oscillation signal output by the numerically controlled oscillator 205 to output a high frequency narrowband Dither signal.

The lower part in Figure 4 is an up-conversion circuit to realize the up-conversion function. It may include multiple frequency conversion circuits to up-convert the input signal provided by the baseband unit 10 to obtain an intermediate frequency input signal. Then, in the adder 206 (corresponding to the mixer 40 in FIG. 2 ), the Dither signal output by the Dither signal generating circuit is mixed with the IF input signal output by the up-conversion circuit to obtain an IF mixed input signal.

The control signal output by the adaptive controller 90 is provided to the numerically controlled oscillator 205 and the coefficient storage finite impulse response filter 202 of the Dither signal generating circuit, respectively controlling the oscillation frequency of the numerically controlled oscillator 205 and the coefficient of the coefficient storage finite impulse response filter 202 , to achieve the purpose of modifying the parameter setting of the Dither signal, thereby adjusting the output Dither signal to adapt to different digital-to-analog converters, changes in the environment, and changes in the input signal.

An example of the adaptive controller 90 of FIG. 2 is shown in FIG. 3 . As shown in FIG. 3 , the adaptive controller 90 mainly includes two parts: one part is a signal spectrum estimation unit 901 , and the other part is an adaptive control unit 902 . The signal spectrum estimation unit 901 processes the distribution of the intermediate frequency mixed signal (ie, the signal before the digital-to-analog conversion) output by the up-converter 30 and the feedback digital input signal (ie, the signal after the digital-to-analog conversion) output by the analog-to-digital converter 80, A corresponding spectral estimate is derived and transmitted to the adaptive control unit 902 . Adaptive control unit 902 actually includes adaptive control algorithms. Through a series of calculations, the control signal can be output to change the Dither signal.

This adaptive process should consist of two phases:

The first stage: Adaptively find the best Dither parameter setting corresponding to the current digital-to-analog converter. In fact, the performance of the Dither signal within a certain range is relatively subtle, and it is enough to find the approximate position at this stage. This step is actually equivalent to a rough adjustment process.

The second stage: Adaptively track the changes of the signal, and obtain the best effect by slightly modifying the settings of the Dither signal. Because as the signal changes, the optimal Dither signal setting will also be slightly different.

The following describes the adaptive control algorithm based on adjusting the frequency of the Dither signal. However, the adjustable control amount should not be limited by the signal frequency, and does not depart from the scope of the method of the present invention. For example, the adjustable control quantity of the Dither signal generator also includes bandwidth, amplitude, etc., and the control method thereof can be fully derived on the basis of the above content for those skilled in the art.

Since the signal area occupies a wide frequency band in the spectrum, and considering the requirements of the filter, the frequency resources available for the Dither signal are limited. Consider the restrictions on the Dither signal when changing.

1. Set the initial Dither frequency f(1) and the initial change value delf(1), and the initial intermediate variable s(1), which represents the change value of the previous few SFDRs.

2. Calculate the change of Dither's effect caused by the i-th change in a loop, and calculate the next frequency change value to determine the frequency of the next digital Dither.

It is assumed that the SFDR value obtained after the i-time spectrum analysis is sfdr(i), and the current change value of sfdr is delsf(i).

Then s(i+1)=(s(i)+sfdr(i))/2

delsf(i)=sfdr(i)-s(i)

delf(i)=sig(delsf(i))*(a(i)*delf(i)+delf2)

f(i+1)=f(i)+delf(i)

Where sig(.) is a sign function, and a is a positive number less than 1. delf2 is a fixed small offset, which is much smaller than delf(1), and this part is used to track the change of the signal. If the Dither signal has exceeded the allowed range, set it to the boundary value. It can be seen that delf(i) will play a decisive role in the early stage and guide the Dither signal to converge to the optimal position. Note that the optimal position is not a fixed position, but within a certain range. In the later stage, delf2 will play a role in tracking signal changes. And make the Dither signal change continuously within a certain range.

Claims (7)

1, a kind of control method of adaptive digital jitter signal comprises the following step:

A. produce the initial number dither signal;

B. described digital jitter signal is also mixed with the input signal up-conversion, produce intermediate frequency mixing input signal;

C. intermediate frequency mixing input signal is carried out digital-to-analogue conversion, produce simulation and mix input signal;

D. simulation is mixed input signal and carry out intermediate frequency filtering, the filtering out of band signal produces analog input signal;

E. analog input signal is carried out analog-to-digital conversion, produce the feedback digital input signal;

F. described feedback digital input signal is composed estimation with above-mentioned intermediate frequency mixing input signal, produce control signal;

G. utilize this control signal, the generation of control figure dither signal; Get back to step b then, so circulation.

2, the method for claim 1 is characterized in that, in described step f, described feedback digital input signal and described intermediate frequency mixing input signal are composed estimation, draw the false dynamic range of nothing of digital-to-analogue conversion process,, produce control signal according to described no false dynamic range.

3, method as claimed in claim 1 or 2 is characterized in that, in described step g, utilizes described control signal, by the frequency of control figure dither signal, and the generation of control figure dither signal.

4, method as claimed in claim 1 or 2 is characterized in that, in described step g, utilizes described control signal, by the bandwidth or the amplitude of control figure dither signal, the generation of control figure dither signal.

5, digital intermediate frequency transmitter comprises:

Base Band Unit is used to provide digital input signals;

Dither signal generator is used to provide dither signal;

Upconverter, the digital input signals that is used for Base Band Unit is provided carries out up-conversion, produces the intermediate frequency digital input signals;

Blender mixes the described dither signal that described dither signal generator provides with the described intermediate frequency digital input signals that described upconverter produces, produce intermediate frequency mixing input signal;

Digital to analog converter carries out digital-to-analogue conversion with mixed intermediate frequency mixing input signal, produces simulation and mixes input signal;

Intermediate-frequency filter links to each other with described digital to analog converter, and the filtering simulation mixes the intermediate-freuqncy signal in the input signal, produces analog input signal;

Radio frequency unit receives the analog input signal that described intermediate-frequency filter produces, and carries out radio frequency processing,

It is characterized in that,

Described digital intermediate frequency transmitter also comprises feedback branch, and this feedback branch comprises:

Analog to digital converter links to each other with described intermediate-frequency filter, and the analog input signal that described intermediate-frequency filter is produced carries out analog-to-digital conversion, produces the feedback digital input signal;

Adaptive controller, link to each other with the output of described upconverter and the output of described analog to digital converter, the feedback digital input signal that is used for producing according to described analog to digital converter is composed estimation with the intermediate frequency mixing input signal that described blender produces, produce control signal, this control signal is input in the described dither signal generator, is used to control described dither signal generator and produces dither signal.

6, digital intermediate frequency transmitter as claimed in claim 5, it is characterized in that, described adaptive controller comprises spectral estimation unit and self-adaptive controller, described spectral estimation unit is composed estimation to described feedback digital input signal and described intermediate frequency mixing input signal, draw the false dynamic range of nothing of digital-to-analogue conversion process, according to described no false dynamic range, produce control signal.

7, digital intermediate frequency transmitter as claimed in claim 5, it is characterized in that, described dither signal generator comprises the tandom number generator that is used to produce the random number signal, the coefficient storage finite impulse response filter, to become the cascaded integrator-comb interpolation filter of the digital signal of higher rate than the digital signal of low rate, the signal that is used to produce the digital controlled oscillator of plural digital intermediate frequency oscillator signal and is used for described cascaded integrator-comb interpolation filter is exported and the plural digital intermediate frequency oscillator signal of described digital controlled oscillator output multiply each other, with the multiplier of output high-frequency narrow-band dither signal.

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