JPH05110441A - Prediction output d/a converter - Google Patents

Abstract

PURPOSE:To reduce a delay time from an input signal of an arithmetic operation circuit till a PWM output by implementing prediction PWM conversion based on data of one preceding sample or over. CONSTITUTION:A prediction output PWM converter 9 uses a PWM conversion synchronizing signal 7 to fetch an output of one preceding sample from an arithmetic operation circuit 3 stored in a delay element 8 simultaneously as the sampling of an A/D converter 2 and applies PWM conversion into a positive or a negative pulse. This is the prediction PWM conversion. After the arithmetic operation in the circuit 3 is finished, an error between the output of one preceding sample stored in the element 8 from the circuit 3 and an output of the circuit 3 substantially to be PWM-converted is calculated. Then the positive or negative correction pulse is outputted in a timing after lapse of a prescribed time after the prediction PWM conversion is started. As a result, the entire delay time is considerably reduced regardless of the arithmetic operation time by the arithmetic operation circuit 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a calculation process for an input signal of a digital servo circuit or the like and a D / D calculation result.
It relates to a system that needs to process A conversion as fast as possible.

[0002]

2. Description of the Related Art In recent years, with the improvement of digital signal processing technology, signals that have been conventionally analog processed have been digitally processed. Along with this, servo circuits and the like are also shifting from conventional analog circuits to digital circuits.

A conventional example of a signal processing section from A / D conversion to D / A conversion, which is a part of a digital servo circuit, will be described below. FIG. 6 shows an example of a conventional signal processing unit from A / D conversion to D / A conversion. In FIG. 6, reference numeral 2 is an A / D converter, which converts the input analog signal 1 into a digital signal in synchronization with the A / D conversion synchronizing signal 6. Reference numeral 3 denotes an arithmetic circuit for performing a predetermined filtering arithmetic operation on the output digital signal of the A / D converter 2, and 4 denotes PWM for synchronizing the output signal of the arithmetic circuit 3 with the PWM conversion synchronizing signal 7. P to convert and output
It is a WM converter.

The operation of the conventional digital servo circuit configured as described above will be described below. First, FIG. 7 shows the timing of each signal shown in FIG. The input analog signal 1 is sampled at a constant cycle by the A / D conversion synchronization signal 6 as shown in (a) and (b) of FIG. Then, the analog signal is converted into a digital signal by the A / D converter 2, and is output at a constant cycle as shown in FIG. 7C. Next, the arithmetic circuit 3 receives the output signal of the A / D converter 2 and performs a filtering operation on each signal. Since the calculation time in the calculation circuit 3 varies depending on the processing path, the calculation time is shown in FIG.
As shown in, the calculation time for each sample data is not constant. Therefore, the output signal of the arithmetic circuit 3 is also not output in a constant cycle. Then, the PWM converter 4 must always start the PWM conversion after the arithmetic processing in the arithmetic circuit 3 is completed. Therefore, as shown in FIG. 7 (f), the PWM conversion synchronization signal 7 has a constant cycle, and the timing at which the PWM conversion is started after the calculation is completed even when the calculation time in the calculation circuit 3 is the longest. Get up at. Then, the PWM converter 4 starts the PWM conversion in synchronization with the rising edge of the PWM conversion synchronizing signal 7, and when the polarity of the input signal is positive, it is a positive pulse, and when the polarity of the input signal is negative, it is a negative pulse. Is output. After performing the A / D conversion on the input analog signal 1 by such an operation, a predetermined filtering calculation is performed in the arithmetic circuit 3, and the output of the arithmetic circuit 3 is made positive or negative by the PWM converter 4. Convert to pulse and output.

As a result, from the input analog signal 1 to the PWM
The delay time up to the output signal 5 is given by the following equation. However, dAD in the following formula is the delay time in the A / D converter 2,
dPR (MAX) is the longest operation time in the operation circuit 3, and TPWM is the pulse width of the PWM output signal 5. As described above, in the conventional method, the total delay time is always reduced by the arithmetic circuit 3 in any case.
It depends on the longest calculation time of.

[0006]

[Equation 1]

[0007]

However, in the above structure, the delay time from the input analog signal to the PWM output signal is determined by the maximum operation time in the operation circuit, and if the operation time is long, the delay time is large. That is, there is a problem that the phase around the entire servo loop is increased and the phase margin is reduced.

The present invention solves the above-mentioned conventional problems. By starting the PWM conversion before the calculation in the arithmetic circuit is completed, the delay time from the input analog signal to the PWM output signal is very short. It was made for the purpose of doing.

[0009]

In order to solve the above-mentioned problems, a predictive output type D / A converter according to the present invention comprises an arithmetic circuit for performing a certain arithmetic processing on an input signal, and an output signal of the arithmetic circuit. And a PWM converter for converting the PWM into a three-valued PWM signal, and the PWM conversion is performed before the operation of the arithmetic circuit is completed by the value predicted in advance based on the output value of the arithmetic circuit one sample or more before. After the start and the end of the calculation of the calculation circuit, the difference between the predicted value and the value that should be PWM-converted is calculated and a correction pulse is output.

[0010]

According to the present invention, the overall delay time can be greatly reduced irrespective of the calculation time in the calculation circuit, and the correction pulse can be output or the calculation can be performed before the prediction PWM conversion is completed. By outputting the correction pulse at the same time when the calculation in the circuit is completed, the average value of the delay time can be further shortened.

[0011]

(Embodiment 1) An embodiment of the predictive output type D / A converter according to the present invention shown in FIG. 1 will be described below with reference to the drawings. In FIG. 1, the A / D converter 2,
The arithmetic circuit 3 is the same as that shown in FIG. 6 and is given the same number. Then, 8 is a delay element that delays the output signal of the arithmetic circuit 3 by one sample, and 9 is a predictive output type PW using the output of the arithmetic circuit 3 and the output of the delay element 8.
It is a predictive output type PWM converter 9 which outputs an M signal 10.

The operation of the predictive output type D / A converter according to the present invention constructed as above will be described below. First, FIG. 2 is a diagram showing the timing of each signal shown in FIG. In FIG. 2, the input analog signal 1 is A / D
The process of sampling in synchronization with the conversion synchronization signal 6 and taking in the signal A / D converted in the A / D converter 2 into the arithmetic circuit 3 and performing the filtering operation is the same as the conventional example described in FIGS. 6 and 7. Is the same. The predictive output type D / A converter according to the present invention is different from the conventional one in the timing after the PWM conversion synchronization signal 7 shown in (f) of FIG. First, unlike the conventional case, the PWM conversion synchronization signal 7 is sampled by the A / D converter 2 and the delay element 8
The output of the arithmetic circuit 3 one sample before stored in is taken in and PWM converted into a positive or negative pulse. This is prediction P
It becomes WM conversion. Then, after the calculation in the calculation circuit 3 is completed, the error between the output of the calculation circuit 3 one sample before stored in the delay element 8 and the output of the calculation circuit 3 which should be PWM-converted is calculated to obtain the predicted PWM. A positive or negative correction pulse is output at a timing when a fixed time T has elapsed from the time when conversion is started. The value of the delay time T at this time is longer than the longest calculation time in the calculation circuit 3, and the predicted PW
It is set to be longer than the longest period of M conversion. Therefore, at the time of outputting the correction pulse, the arithmetic processing in the arithmetic circuit 3 is always completed, and the predictive PWM conversion is also completed. By such an operation, after the analog input signal 1 is A / D converted, the arithmetic circuit 3 performs a predetermined filtering operation, and the output of the arithmetic circuit 3 is positive or negative by the PWM converter 9. It is converted into a pulse and output.

As a result, from the input analog signal 1 to the PWM
The delay time up to the output signal 5 is given by Equation 2. In the following formula, TYPWM and THPWM are the pulse widths of the predicted PWM conversion pulse and the correction pulse, respectively, and DY and DH are the output of the arithmetic circuit 3 one sample before and the output of the arithmetic circuit 3 that should be PWM-converted. .. Further, T is the time from the start of the predictive PWM conversion to the output of the correction pulse. In general, in the case of a digital servo or the like, when the sampling frequency is sufficiently higher than the servo band, the error from the data one sample before becomes very small. Therefore, DY >> DH. In this case, it can be approximately considered that DH≈0, and the delay time is also approximated as shown in Expression 3.

[0014]

[Equation 2]

[0015]

[Equation 3]

Comparing Equation 1 and Equation 3, the delay time in the predictive output type D / A converter according to the present invention is A / D.
It can be said that the delay time is much shorter than that of the conventional method, regardless of the conversion time of the converter 2 and the calculation time of the arithmetic circuit 3.

(Embodiment 2) The embodiment described above is the case according to the third claim. The predictive output type D / A converter according to the present invention is not limited to the above-mentioned embodiment, and the system according to claim 4 is also possible. An example of this case will be shown below.

The circuit configuration of the second embodiment is also the same as that shown in FIG. The timing of each signal is as shown in FIG. In FIG. 3, first, in the PWM conversion during the PWM period (1), the output of the arithmetic circuit 3 one sample before is “+”.
3 ”, the pulse width of the predictive PWM conversion pulse is“ +
3 ”. Then, after that, the arithmetic circuit 3 completes the arithmetic operation, and when it is found that the originally output value is "+4", a pulse of "+1" is added as a correction pulse. This operation is the same as the operation already described in the first embodiment. Next, in the PWM conversion during the PWM period (2), since the output of the arithmetic circuit 3 one sample before is “+4”, the pulse of the predictive PWM conversion pulse as shown by the dotted line in (d) of FIG. Try to make the width "+4". However, it is understood that the calculation in the arithmetic circuit 3 is completed before the predictive PWM conversion is completed, and the value to be originally output is “+2”. In this case, the predictive PWM conversion is finished at this point, and the pulse of "-1" is added as the correction pulse (the pulse width at this time is "+3"). As a result, a pulse corresponding to "+2" is output as a whole.

As described above, the predictive output type D / A converter according to the second embodiment outputs the correction pulse before the predictive PWM conversion is completely completed. It is possible to shorten the fixed time T from the start of PWM conversion to the output of the correction pulse. By doing so, the delay time shown in Expression 3 can be further shortened as compared with the first embodiment.

(Embodiment 3) The first and second embodiments described above
The embodiment of the present invention is a system in which a correction pulse is output after a fixed time has elapsed after starting the predictive PWM conversion based on the second claim. Predictive output type D / according to the present invention
In addition to the above-described embodiment, the A converter may be based on the method according to the fifth aspect of the invention. An example of such a case is shown below. First, a method according to claim 6 will be described as a third embodiment among methods according to claim 5.

The circuit configuration of the third embodiment is also the same as that shown in FIG. The timing of each signal is as shown in FIG. As is apparent from FIG. 4, in the third embodiment, the timing of outputting the correction pulse is always the same as the end of the arithmetic operation in the arithmetic circuit 3. Therefore, unlike the above embodiment, the delay times T (1), T (2), and T (3) from the start of the predictive PWM conversion to the output of the correction pulse are calculated by the calculation processing time dPR ( 1), dPR (2), dPR
It does not necessarily match because it is determined by (3).

In the first embodiment described above, the timing for outputting the correction pulse is determined by the longest operation time in the arithmetic circuit 3, and it is not necessary until the correction pulse is output after the arithmetic circuit 3 completes the arithmetic operation. There was a wait.
However, in the third embodiment, since the waiting time from the end of the calculation in the calculation circuit 3 to the output of the correction pulse is always zero, the correction after the predictive PWM conversion is started in each PWM period. The delay time until the pulse is output can always be minimized. According to such a method, the third embodiment has a more mathematical formula 3 than the first embodiment.
The delay time shown in can be further shortened.

(Embodiment 4) The third embodiment described above is a system based on the sixth claim.
The predictive output type D / A converter according to the present invention is not limited to the above-described embodiment, and may be based on the method according to claim 7. An embodiment in this case will be shown below as a fourth embodiment of the present invention.

The circuit configuration of the fourth embodiment is the same as that shown in FIG. The timing of each signal is as shown in FIG. As is apparent from FIG. 5, in the fourth embodiment as well as in the third embodiment, the correction pulse is output immediately after the calculation in the arithmetic circuit 3 is completed. Then, when the calculation in the arithmetic circuit 3 is completed before the completion of the predictive PWM conversion as in the PWM period (2) shown in FIG. 5, the predictive PWM conversion is completed at that time as in the second embodiment. Then, as a result, the correction pulse is output so that the total pulse value becomes equal to the value to be PWM-converted originally. That is, the fourth embodiment is a system in which the second embodiment and the third embodiment are combined.

As described above, in the fourth embodiment, the individual PW
In the M period, the delay time from the start of the predictive PWM conversion to the output of the correction pulse can always be set to the shortest, and the width of the predictive PWM conversion pulse can be set longer than the timing at which the arithmetic operation of the arithmetic circuit 3 ends. Is possible. With such a method, the third embodiment can further reduce the delay time shown in the mathematical expression 3 as compared with the first embodiment, the calculation time in the arithmetic circuit 3 is short, and the prediction PWM conversion period is short. Even if the length is long, it is possible to deal with it.

In each of the above embodiments, the value for predictive PWM conversion is 1 based on the eighth claim.
It was obtained by holding the previous value of the data before sampling,
It is also possible to obtain it by the primary hold with the data two samples before and the data one sample before as described in claim 9 above.

[0027]

As described above, the predictive output type D / A converter according to the present invention uses an arithmetic circuit for performing a certain arithmetic processing on an input signal and a ternary PW for the output signal of the arithmetic circuit.
A PWM converter for converting into an M signal, and PWM conversion is started before the operation of the arithmetic circuit is completed by a value predicted in advance based on the output value of the arithmetic circuit one sample or more before, After the calculation of (3) is completed, the error amount between the predicted value and the value that should be PWM-converted is calculated and the correction pulse is output, so that the entire delay time is irrelevant to the calculation time in the calculation circuit. It is possible to greatly reduce the delay time by outputting the correction pulse before the predictive PWM conversion is completed, or by outputting the correction pulse at the same time when the calculation in the arithmetic circuit is completed. This has the effect of shortening the average value.

[Brief description of drawings]

FIG. 1 is a predictive output type D of a digital servo according to the present invention.
/ A converter configuration diagram

FIG. 2 is a diagram showing the timing of each signal in the first embodiment.

FIG. 3 is a diagram showing the timing of each signal in the second embodiment.

FIG. 4 is a diagram showing the timing of each signal in the third embodiment.

FIG. 5 is a diagram showing the timing of each signal in the fourth embodiment.

FIG. 6 is a configuration example of a signal processing unit of a conventional digital servo.

FIG. 7 is a diagram showing timings of signals of respective parts in the conventional example.

[Explanation of symbols]

 2 A / D converter 3 Arithmetic circuit 4 PWM converter 8 Delay element 9 Predictive output type PWM converter

Claims (9)

[Claims] 1. An arithmetic circuit having one or more samples before, which has an arithmetic circuit for performing a certain arithmetic processing on an input signal and a PWM converter for converting an output signal of the arithmetic circuit into a ternary PWM signal. Based on the value predicted in advance based on the output value of P, the PWM conversion is started before the calculation of the calculation circuit is completed, and after the calculation of the calculation circuit is completed, the predicted value and the original P
A predictive output type D / A converter characterized by calculating an error from a value to be WM-converted and outputting a correction pulse. 2. The predictive output type D / according to claim 1, wherein the timing of outputting the correction pulse is set to a predetermined time after starting the predictive PWM conversion.
A converter. 3. The method according to claim 2, wherein the timing of outputting the correction pulse is set to a fixed time after the start of the predictive PWM conversion and after the longest period of the predictive PWM conversion. Predictive output type D / A converter. 4. The predictive PWM is set such that the timing of outputting the correction pulse is a fixed time after the predictive PWM conversion is started and before the longest period of the predictive PWM conversion.
When the conversion pulse and the correction pulse overlap, the predictive PWM conversion is stopped midway, and the width of the correction pulse is further corrected so that the overall pulse value matches the value that should be PWM-converted. The predictive output type D / A converter according to claim 2. 5. The predictive output type D / according to claim 1, wherein the timing of outputting the correction pulse is a time point when the arithmetic processing of the arithmetic circuit is completed.
A converter. 6. The method according to claim 5, wherein the timing of outputting the correction pulse is set to a time point when the arithmetic processing of the arithmetic circuit is completed and after the longest period of the predictive PWM conversion. Predictive output type D / A converter. 7. The predictive PWM is set such that the timing of outputting the correction pulse is the time when the arithmetic processing of the arithmetic circuit is completed and before the longest period of the predictive PWM conversion.
When the conversion pulse and the correction pulse overlap, the predictive PWM conversion is stopped midway, and the width of the correction pulse is further corrected so that the overall pulse value matches the value that should be PWM-converted. The predictive output type D / A converter according to claim 5. 8. The predictive output type D / A converter according to claim 1, wherein the predictive value is obtained by holding the previous value of the output value of the arithmetic circuit one sample before. 9. The predicted output type D according to claim 1, wherein the predicted value is obtained by first holding an output value of an arithmetic circuit one sample before and two samples before.
/ A converter.