JP2552304B2 - Offset compensation circuit - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention converts an analog signal into a digital signal.
The present invention relates to an offset compensating circuit for compensating for a DC offset generated in a circuit system including an A / D converter.

[Technical background of the invention and its problems]

FIG. 4 is a schematic configuration diagram of a circuit system having an A / D converter including a conventional offset compensation circuit.

In the figure, reference numeral 1 is an A / D converter for converting an input analog signal into a digital signal, and 2 is a code detecting means, which is an MSB latch circuit for detecting only a sign bit of a digital signal output OUT from the A / D converter 1. , Or pulse width modulation wave generating means for extracting data of higher-order multiple bits from the digital signal output OUT and generating a PWM (Pulse Width Modulation) wave according to the extracted data of higher-order multiple bits. . Reference numeral 3 is an integrator that integrates the digital data detected by the code detection means 2 to generate an offset correction voltage V _CMP , and 4 is band limited to the input analog signal IN and passes only the required band component. It is a filter for inputting to the A / D converter 1.

The filter 4 is composed of, for example, an active filter using an operational amplifier or the like, and the offset correction voltage V _CMP from the integrator 3 is supplied to the input terminal of the operational amplifier used for the active filter to output the output. Feedback is applied to the circuit system so that the positive and negative probabilities of the sign of the digital signal OUT become equal. Therefore, the offset of the output digital signal OUT is automatically compensated for based on the configuration shown in FIG.

In the configuration described above, for example, when a music signal is input, the sign detection means 2 outputs positive and negative sign bits. Usually, since the music signal appears statistically with equal positive and negative probabilities, the offset of the digital output is compensated by applying feedback based on the sign bit detected by the sign detecting means 2. Also the input signal
When IN is signalless, feedback is applied so that the digital signal output OUT changes between the positive minimum value and the negative minimum value.

By the way, when adjusting the offset of the A / D converter,
By opening the feedback loop configured as described above, it is necessary to perform accurate offset adjustment so that the digital code of the output becomes zero in the state where the servo is not applied.

However, the above-described conventional offset compensating circuit has the code detecting means 2 after the A / D conversion by the A / D converter 1.
The digital data detected by the above is integrated by the integrator 3 to generate the offset correction voltage V _CMP, and the offset correction voltage V _CMP generated based on the digital data after the A / D conversion is _supplied to the filter 4 It is configured to perform offset compensation in the A / D converter 1 by feeding back through the analog signal input section.

Therefore, even when the offset of the A / D converter 1 is adjusted, since the feedback loop is formed, the servo is applied and the offset is always zero.
There is a problem that it is difficult to perform accurate offset adjustment.

[Object of the Invention]

The present invention was made in order to eliminate the above-mentioned conventional problems, and provided with a switching means for opening the feedback loop of the circuit system when adjusting the offset of the A / D converter,
It is an object of the present invention to provide an offset compensating circuit capable of performing accurate offset adjustment in a state where no servo is applied by switching the switching means.

[Outline of Invention]

In order to generate the offset adjustment voltage based on the offset compensation voltage obtained based on the digital data from the A / D converter obtained by A / D conversion and other digital data different from the digital data, A / above
A switching means is provided for switching between digital data from the D converter and other digital data.When the offset of the A / D converter is adjusted, the feedback loop is opened by the above switching means so that servo is not applied. It enables accurate offset adjustment based on the digital data of.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of an offset compensation circuit according to the present invention.

In the figure, the A / D converter 1, the code detecting means 2, the integrator 3, and the filter 4 are the same as those shown in FIG. 4 described as a conventional example. In the present invention, the feedback loop is opened during the offset adjustment of the A / D converter 1 between the code detecting means 2 and the integrator 3 which form a feedback loop by being interposed in the circuit system for offset compensation. The integrator 3 is provided with a switching means including a switch 5 for supplying other digital data different from the digital data obtained by A / D conversion.

Therefore, when the A / D conversion operation is performed, the switch 5
Is on the side of contact point a, and only the required band component of the input analog signal IN is taken out by the filter 4 and supplied to the A / D converter 1 and output from the A / D converter 1 as a digital signal output OUT. Further, the output digital signal output OUT from the A / D converter 1 is supplied to the code detecting means 2 described above, and the digital data obtained by the code detecting means 2 is supplied to the integrator 3 via the contact a side of the switch 5.
To the offset compensating voltage after being integrated by the integrator 3. Then, this offset compensation voltage is fed back through the analog signal input section of the filter 4 and the offset compensation of the above-mentioned circuit system is performed.

When the offset of the A / D converter 1 is adjusted, the switch 5 is switched to the contact b side, the feedback loop of the circuit system described above is opened, and the integrator 3 is supplied with other digital data from the terminal 6. Then, based on the other digital data supplied to the integrator 3, the integrator 3
Offset compensation voltage is generated from the A / D converter 1
The offset adjustment is performed by adjusting the offset adjusting means (not shown) so that the digital code of the output at 0 becomes zero. In this case, the contact b from the terminal 6 to the switch 5
A desired offset can be created by arbitrarily selecting the duty ratio of other digital data supplied to the integrator 3 via the offset in the A / D converter 1 so as to adjust the offset. Adjustments can be made arbitrarily.

The switch 5 as the switching means described above can be formed by using one gate in the digital IC including the code detecting means 2. That is, since the feedback loop can be opened in the digital IC, simple and reliable switching control can be performed as compared with the case where the feedback loop is opened in the analog section including the integrator 3 and the filter 4. it can.

FIG. 2 is a block diagram showing a second embodiment of the offset compensation circuit according to the present invention.

Also in the case of the second embodiment, the offset compensation when the A / D conversion operation is performed is performed in exactly the same manner as in the case of the first embodiment.

Then, when adjusting the offset of the A / D converter 1,
The switch 5 is switched to the contact b side, the feedback loop of the circuit system is opened, and the duty ratio is 50% from the terminal 6.
Is supplied to the integrator 3 via the contact b of the switch 5.

As described above, it is necessary to perform the offset adjustment in the state where the servo is not applied by opening the feedback loop of the circuit system. However, in the second embodiment, when the offset adjustment of the A / D converter 1 is performed, the duty ratio of 50% is used. Supplying the digital data to the integrator 3 is equivalent to stopping the operation of the offset compensation circuit.
Therefore, in the second embodiment, the accuracy of the offset adjustment in the A / D converter 1 can be improved and the offset adjustment can be easily performed.

FIG. 3 is a block diagram showing the third embodiment of the present invention. This type is configured to perform accurate offset compensation even in the type that also performs A / D conversion and D / A conversion.

In the figure, 7 is a switch that is switch-controlled during A / D conversion and D / A conversion, and 8 is an A / D-D / A dual-purpose converter that performs A / D conversion and D / A conversion by switching.
Although not shown in the figure through the A / D-D / A dual-purpose converter 8, a digital signal processor (DSP: Digital Sign Processor) for performing signal processing associated with A / D conversion and D / A conversion.
al Processer) and the like.

In the A / D conversion mode, the switches 7 and 5 are controlled to be switched to the contact a side based on the control of the signal processing unit described above, and the A / D-D / A combined converter 8 is switched to the A / D conversion mode. To be At this time, the input analog signal is supplied to the filter 4 via the contact a side of the switch 7 to perform the required band limitation, and then is digitalized by the A / D converter section of the A / D-D / A dual-purpose converter 8. The converted signal is subjected to the required signal processing by the signal processing section, and the digital data detected by the code detecting means 2 is supplied to the integrator 3 via the contact a side of the switch 5 to be integrated, and this output The offset correction voltage is output.
Then, the offset correction voltage obtained at the output of the integrator 3 is fed back through the analog signal input section of the filter 4, and the offset compensation of the circuit system is performed.

On the other hand, in D / A conversion mode, switches 7 and 5
Is controlled to be switched to the contact b side based on the control of the signal processing unit described above, and the A / D-D / A dual-purpose converter 8 is D / A.
Switch to conversion mode. Then, in the D / A conversion mode, the digital data subjected to the required signal processing in the signal processing unit is converted into an analog signal by the D / A converter unit of the A / D-D / A dual-purpose converter 8, and the digital data of the switch 7 is converted. The analog output at the time of D / A conversion is supplied to the filter 4 via the contact b side and is taken out from the terminal 9.

Further, in the D / A conversion mode, the switch 5 as the switching means is controlled to switch to the contact b side as described above, the feedback loop of the offset compensation circuit in the A / D conversion mode is opened, and the terminal 6 to 50% duty ratio
Is supplied to the integrator 3 via the contact b side of the switch 5. That is, in the D / A conversion mode, since the voltage fed back from the output of the integrator 3 to the filter 4 must be constant, digital data having a duty ratio of 50% is supplied from the terminal 6 and the duty ratio 50 % Digital data is integrated by the integrator 3, and the output of the integrator 3 is always kept constant to perform D / A conversion.

[Effect]

According to the present invention described above, since the switching means for opening the feedback loop of the offset compensation circuit at the time of adjusting the offset of the A / D converter is provided, the output of the A / D converter is switched by switching the switching means. Since the offset adjusting voltage is generated by generating the offset adjusting voltage based on the other digital data different from the obtained digital data, the accurate offset adjustment can be performed without the servo.

[Brief description of drawings]

FIG. 1 is a block configuration diagram showing a first embodiment of an offset compensation circuit according to the present invention, FIG. 2 is a block configuration diagram showing a second embodiment of the present invention, and FIG. 3 is a third embodiment of the present invention. FIG. 4 is a block diagram showing an embodiment, and FIG. 4 is a block diagram showing a conventional offset compensation circuit. 1 ... A / D converter, 2 ... sign detection means, 3 ... integrator, 4 ... filter, 5 ... switch (switching means),
8 ... A / D-D / A dual-purpose converter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichi Wakumura 42610 Hanazono, Tokorozawa-shi, Saitama Pioneer Co., Ltd. Tokorozawa Plant (72) Inventor Yoshimi Iso 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Home Appliances Research Laboratory, Hitachi, Ltd. (72) Hiroo Okamoto 292 Yoshida-cho, Totsuka-ku, Yokohama City, Kanagawa Prefecture Home Appliances Research Laboratory, Hitachi, Ltd. (56) Reference JP 62-104221 (JP, A) JP 59-153490 (JP, A)

Claims (1)

(57) [Claims] 1. An A / D converter that converts an input analog signal into a digital signal, and an integrator that generates an offset compensation voltage based on output data from the A / D converter, and output from the integrator. In an offset compensation circuit for compensating an offset generated at the time of A / D conversion operation by forming a feedback loop for feeding back an offset compensation voltage to the input analog signal, an offset adjusting means for adjusting the offset of the A / D converter system. An input terminal for inputting adjustment digital data, and switching means for selectively supplying either one of the signal from the A / D converter and the signal input from the input terminal to the integrator. The switching means supplies a signal from the A / D converter to the integrator during the A / D conversion operation to perform the offset adjustment. The offset compensating circuit is characterized in that when the offset is adjusted by means, the switching means is switched to the input terminal and a pulse signal having a duty ratio of 50% is supplied from the input terminal to the integrator.