JPH03132885A - Offset compensating circuit - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution and to reduce the circuit scale by deriving a difference between a converted digital signal, and a digital offset value held in a register by an arithmetic circuit, and compensating an offset of an analog circuit. CONSTITUTION:By converting an output signal for showing an offset value at the time when an analog signal inputted to an analog circuit 1 is set to zero, to a digital signal by an A/D converter 2 and holding it in a register 4, an analog output signal processed by the analog circuit 1 is converted to a digital signal by the A/D converter 2 and inputted to a digital circuit 3. In this case, by deriving a difference between the digital offset value held in the register 4 and the output digital signal of the A/D converter 2 by an arithmetic circuit 5, a digital signal whose offset is compensated can be inputted to the digital circuit 3. In such a way, the circuit scale can be reduced, and also, the automation can be executed.

Description

[Detailed Description of the Invention] [Summary] This invention relates to an offset compensation circuit that compensates for the offset of analog circuits such as operational amplifiers, and aims to reduce the circuit scale and enable automation. The output signal of the circuit is A
The offset compensation circuit comprises a digital circuit that converts the signal into a digital signal using a D converter and inputs the digital signal, and compensates for the offset of the analog circuit. an operation for converting the output signal of the analog circuit that processed the analog signal into a digital signal by the AD converter, and outputting the difference between the digital signal and the digital offset value held in the register; It was constructed by providing a circuit.

[Industrial application field]

The present invention relates to an offset compensation circuit that compensates for the offset of an analog circuit such as an operational amplifier.

A configuration in which an analog input signal is processed by an analog circuit such as an operational amplifier and then converted into a digital signal by an AD converter for processing by a processor is applied to various devices. In this case, an offset occurs due to a difference in base-emitter voltage, a difference in base bias current, etc. of the transistors in the first-stage differential pair of the analog circuit. It is necessary to compensate for this offset to improve the accuracy of signal processing.

[Conventional technology]

Analog circuits that amplify analog input signals such as measurement signals from sensors, and analog circuits that perform processing such as addition and amplification of analog input signals such as audio signals, include operational amplifiers and various types of processing such as amplification, comparison, and addition. The operational amplifier generally includes a differential amplifier in the first stage. 20 Even when a differential amplifier is constructed from a semiconductor integrated circuit, differences in base-emitter voltage and base bias current of the differential pair of transistors on the same semiconductor chip occur, resulting in an offset. occurs. Therefore, since the offset is added to the output signal of the analog circuit, an error will occur.

In order to cancel out such offsets, various offset compensation circuits have been proposed.For example, there are known configurations in which a compensation voltage of opposite polarity to the offset voltage is added to the output signal, and a configuration in which a compensation voltage is added to the input stage. ing.

[Problem that the invention seeks to solve]

As mentioned above, conventional offset compensation circuits generally have a configuration in which an analog compensation voltage is added to the analog input signal or analog output signal of the analog circuit to compensate.
Since the offset is compensated by analog configuration,
This has the disadvantage that the circuit configuration becomes complicated and the circuit scale becomes large.

The present invention aims to reduce the circuit scale and also enable automation.

[Means to solve the problem]

The offset compensation circuit of the present invention compensates for offset by digital processing, and will be explained with reference to FIG.

The output signal of the analog circuit 1 that processes the analog signal is
It is equipped with a digital circuit 3 such as a processor that converts into a digital signal by an AD converter 2 and inputs it, a register 4 that converts the offset value of the analog circuit 1 into a digital signal by the AD converter 2 and holds it, and a register 4 that processes the analog signal. An arithmetic circuit 5 is provided which converts the output signal of the analog circuit 1 into a digital signal by an AD converter 2 and outputs the difference between this digital signal and a digital offset value held in a register 4.

[Effect]

An output signal indicating an offset value when the analog signal input to the analog circuit 1 is set to zero is converted into a digital signal by the AD converter 2 and held in the register 4. When the output signal is converted into a digital signal by the AD converter 2 and inputted to the digital circuit 3, the arithmetic circuit 5 calculates the difference between the digital offset value held in the register 4 and the output digital signal of the AD converter 2. By determining , it is possible to input a digital signal whose offset has been compensated for into the digital circuit 3 .

〔Example〕

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

FIG. 2 is a block diagram of an embodiment of the present invention, in which 11 is an operational amplifier as an example of an analog circuit, 12 is an AD converter, 1
3 is a processor which is an example of a digital circuit, 14 is a register, 15 is an adder which is an example of an arithmetic circuit, 16 is a polarity inversion circuit, and 17 is a changeover switch.

When power is turned on, selector switch 1 is activated by a control signal.
7 is switched from the contact a side to the contact side, and a reference level signal, for example, a ground potential, is input to the operational amplifier 11. The output signal of the operational amplifier 11 at that time is converted into a digital signal by the AD converter 12, and the register 1 is converted according to the control signal.
4 is held as a digital offset signal.

Then, the changeover switch 17 is switched from the contact side to the contact a side by the control signal, and measurement signals such as temperature, voltage, current, etc., and analog input signals such as audio signals are input to the operational amplifier 11, and the operational amplifier 11 amplifies. The output signal is sent to the AD converter 12
The signal is converted into a digital signal and input to the processor 13 via the adder 15.

At this time, the polarity of the digital offset signal output from the register 14 is inverted by the polarity inverting circuit 16 and added to the adder 15, so that the processor 13
Digital output signal from AD converter 12
The offset signal is subtracted, and a digital signal from which the offset of the operational amplifier 11 is compensated is input.

Therefore, the processing by the processor 13 is accurate and is not affected by the offset of the operational amplifier 11 of the analog circuit.

Furthermore, by switching the changeover switch 17 to the contact side at any time, it is possible to update the contents held in the register 14 in accordance with changes in the offset of the operational amplifier 11, thereby coping with changes in the operational amplifier 11 over time.

It is also possible to provide the polarity inversion circuit 16 before the register 14. Furthermore, if a subtracter is used in place of the adder 15, the polarity inversion circuit 16 can be omitted. It is also possible to adopt a configuration in which the offset of the operational amplifier 11 is measured in advance and set in the register 14 as a digital offset value. In that case, selector switch 1
7 can be omitted.

Further, when the number of bits of the AD converter 12 is about 10 to 16, the register 14 only needs to have a bit capacity of about 2 to 5 lower bits. Of course, the present invention can also be applied to various analog circuits other than the operational amplifier 11.

〔Effect of the invention〕

As explained above, the present invention allows the offset value of the analog circuit 1 such as an operational amplifier to be digitally stored in the register 4.
The digital offset value held in the register 4 and the digital signal converted by the AD converter 2 for adding an output signal from the analog circuit 1 to the digital circuit 3 such as a processor are stored as an offset value. The difference is calculated by the arithmetic circuit 5 to compensate for the offset of the analog circuit 1. Since the offset is compensated digitally, the circuit configuration is simplified and the circuit scale can be reduced. There are advantages.

Furthermore, it is also possible to automatically measure the offset of the analog circuit 1 and set it in the register 4 using a control signal at the initial stage such as when the power is turned on, so that offset compensation of the analog circuit 1 can be automated. It is easy to do.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention. 1 is an analog circuit, 2 is an AD converter, 3 is a digital circuit, 4 is a register, and 5 is an arithmetic circuit. Analog input signal E-principal diagram of the present invention Fig. 1

Claims (1)

[Scope of Claims] A digital circuit (3) that converts an output signal of an analog circuit (1) that processes an analog signal into a digital signal by an AD converter (2) and inputs the digital signal, the analog circuit (1) An offset compensation circuit that compensates for the offset of the analog circuit (1) includes: a register (4) that converts the offset value of the analog circuit (1) into a digital signal by the AD converter (2) and holds the digital signal; and a register (4) that processes the analog signal. an arithmetic circuit that converts the output signal of the analog circuit (1) into a digital signal by the AD converter (2) and outputs the difference between the digital signal and the digital offset value held in the register (4); 5) An offset compensation circuit characterized by comprising: