JPS62194468A - Rectifying circuit - Google Patents

Abstract

PURPOSE:To reduce the error of an output current due to input offset, by a method wherein the output current of an operational amplifier is negatively fed back by a current mirror circuit and controlled in accordance with negative feedback quantity by the operation of the operational amplifier. CONSTITUTION:Transistors Q1, Q2 constitute a first current mirror circuit and transistors Q11, Q12 constitute a second current mirror circuit. Now, when it is supposed that an input signal Vin has a level higher than that of reference voltage Vref, a current Ia flows through an input resistor Ra, while a current Ia/2 flows to the transistor Q1 as a reference current and sucked in the output side of an operational amplifier 1 through a resistor R2. The current Ia/2 corresponding to the above mentioned reference current also flows to the transistor Q2 as an output signal and output voltage Va is obtained as the voltage drop of an output resistor R11. Vb is obtained in the same way as such as case that voltage Vin has a level lower than that of voltage Vref and rectifying output is alternately obtained from the resistors R11, R12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rectifier circuit suitable for application to various electronic equipment such as industrial measuring equipment and low frequency audio equipment.

[Conventional technology]

Rectifier circuits are often used when obtaining a control signal in response to an increase in the level of an analog signal, or when displaying the level. The simplest rectifier circuit is one that utilizes the so-called rectifying characteristics of diodes.

However, it is known to those skilled in the art that diodes are not ideal elements and have large errors, especially when the input signal is small.

In addition, "Practical Design of Analog Circuits" (March 3, 1981)
First published on October 0, published by CQ Publishing, pp. 79-82), a rectifier circuit that combines the above-mentioned diode and operational amplifier is shown as an absolute value circuit.

[Problem that the invention seeks to solve]

According to the studies of the present inventors, in a rectifier circuit using an operational amplifier, unless a negative feedback circuit is configured, the input offset voltage of the operational amplifier cannot be compensated for, and as shown in FIGS. It turned out to be an error in the characteristics. That is, errors shown as A and B appear in the drawing.

Even if a negative feedback circuit is provided to eliminate the above error,
Since most current electronic devices are actually formed from semiconductor integrated circuits, it is desirable to avoid using diodes.

From this point of view, we have considered obtaining a rectifier circuit that reduces errors due to input offset by providing a negative feedback circuit with a simple circuit configuration consisting of an operational amplifier and a transistor, and have arrived at the present invention.

SUMMARY OF THE INVENTION An object of the present invention is to provide a rectifier circuit that has a simple circuit configuration and reduces errors between input signals and output signals.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for solving problems]

A brief overview of typical inventions disclosed in this application is as follows.

That is, the non-inverting input terminal of the operational amplifier is set to a reference potential, the input signal is supplied to the inverting input terminal via the input resistor, and the input signal is connected between the inverting input terminal and the output side of the operational amplifier. a first current mirror circuit that obtains an output current by using a current that flows when the signal is at a high level with respect to the reference potential as a reference current; and a first current mirror circuit that obtains an output current by using a current that flows when the signal is at a high level with respect to the reference potential; A second current mirror circuit that obtains an output current by using the flowing current as a reference current, and a resistor for adjusting the current that serves as the reference current of the first and second current mirror circuits are provided, and the input offset error is adjusted to the first current mirror circuit. and is reduced by the negative feedback operation by the second current mirror circuit.

[Effect]

According to the above means, the output current of the operational amplifier is negatively fed back by the current mirror circuit, and the output current is controlled according to the amount of negative feedback by the operation of the operational amplifier, so there is an error in the output current due to input offset. This achieves the object of the present invention, which is to obtain a rectifier circuit with a simple circuit configuration and fewer errors.

〔Example〕

Hereinafter, a first embodiment of a rectifier circuit to which the present invention is applied will be described with reference to FIGS. 1 and 2. Note that FIG. 1 is a circuit diagram of the rectifier circuit, and FIG. 2 is a characteristic diagram of an input signal versus an output signal to explain the circuit operation.

The feature of this embodiment is that good rectification characteristics are obtained by providing a negative feedback circuit with a simple circuit configuration consisting of a current mirror circuit in the negative feedback path of the operational amplifier to which the input signal is supplied. .

A non-inverting input terminal + of the operational amplifier 1 is set to a reference voltage Vref.

An input signal V is connected to the inverting input terminal through an input resistor Ra.
in is supplied.

Transistors Q, , Qt constitute a first current mirror circuit according to the present invention.

Transistors Q+I and Qt constitute a second current mirror circuit according to the present invention.

Resistors R+ and Rt are adjustment resistors in the present invention,
The resistance ratio is set to 2 where resistance Rt is resistance Reel.

Assuming now that the input signal Vin is at a higher level than the reference voltage Vref, a current Ia flows through the input resistor Ra. 1/2·Ia flows through the transistor Q as a reference current. This current is sucked into the output side of the operational amplifier 1 via the resistor R1.

On the other hand, the transistor Q2 also has a current of 1 corresponding to the above reference current.
A current of /2・Ia flows as an output signal, and the output resistance R1
, the output voltage Va is obtained as the voltage drop of .

Next, when the input signal Vin is at a lower level than the reference voltage Vref, the output current Ib corresponding to the level difference is
is obtained. The transistor Qtz has a reference current of 1
A current of /2·Ib flows, and further flows to the input resistor Ra via the resistor R.

What should be noted here is that since the resistors R1 and R2 have the above resistance ratio, the reference current flowing through the transistors Q1) and QI2 becomes 1:2. However, since the current Ia is the sum of the reference current and output current of the first current mirror circuit, the currents flowing through the input resistor Ra have the same amount of current.

Therefore, the current Ia flowing in both directions of the input resistance Rak, 1/
The amount of current of 2・Ib is l Vin−Vr e f I
/Ra. That is, the currents Ia, I
The current ratio of b is 1:2, and this current ratio is determined by the adjusting resistors R, , R,.

The reference current flowing through the transistors Q+ and Q12k corresponds to the voltage level of the input signal Vin due to the current mirror circuit and the circuit operation of the operational amplifier 1.

ing. This is because the reference current flowing through the transistor Q, 2k is twice that of 1/2·Ia, so the output resistor R1
This is to make the total current flowing through the output resistor R11 equal to the current flowing through the resistor R11.

Therefore, as shown in FIG. 2, when the input signal Vin changes level around the reference voltage Vref k, Va.

The rectified rectified output as shown as vb is connected to resistor R1
1, R, and 2 alternately.

(1) The non-inverting input terminal of the operational amplifier is set as the reference potential,
By driving the operational amplifier in comparison with the input signal supplied to the inverting input terminal, two current mirror circuits provided in the negative feedback circuit are individually driven in response to changes in the polarity of the input signal. Thus, the effect of obtaining a half-wave rectified output from the current mirror circuit 2 above can be obtained.

(2) According to (1) above, errors caused by offset on the input side of the operational amplifier are negatively fed back by the current mirror circuit, so the output signal from the operational amplifier is corrected, which reduces at least the error caused by offset. The effect of obtaining rectified output can be obtained.

(3) Since the rectifier circuit is constituted by the operational amplifier and the circuit 2, the circuit configuration is simple and it is easy to integrate the circuit into a semiconductor integrated circuit.

(4) With the above (2), the effect of improving the accuracy of industrial measuring instruments, etc. can be obtained.

Although the invention made by the present inventor has been specifically explained based on examples above, the present invention is not limited to the above examples, and can be modified in various ways without departing from the gist thereof. Needless to say.

For example, the resistors R,,,R,, may be replaced by a common load resistance. In this case, the rectified output is double-wave rectified.

It is preferable that the current mirror circuit (2) has a circuit configuration in which the ratio between the reference current and the output current is more accurate, such as a Wilson type circuit. An example is shown in FIG. This is because although the current is accurately determined by Vin-Vμl- due to the high gain of the operational amplifier, if the current mirror ratios of the current mirrors interposed in the negative feedback path are different, this will eventually cause an offset to occur.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

That is, since a negative feedback circuit consisting of two current mirror circuits is configured in the negative feedback path of the operational amplifier, a rectified output with input offset corrected can be obtained with a simple circuit configuration.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a rectifier circuit showing a first embodiment of the present invention, Fig. 2 is a characteristic diagram of an input signal versus an output signal explaining the entire circuit operation of the rectifier circuit, and Fig. 3 is a circuit diagram of a rectifier circuit according to a first embodiment of the present invention. FIG. 4 is a first characteristic diagram of the rectifier circuit studied, FIG. 4 is a second characteristic diagram of the rectifier circuit studied prior to the present invention, and FIG. 5 is a circuit diagram showing a second embodiment of the present invention. be. 1... Operational amplifier, Q, ~Q+2... Transistor, Vref... Reference voltage, Ra... Input resistance, R,
, Rt... current adjustment resistor, Ia, Ib... current,
Va, Vb... Rectified output. Figure 1 Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] 1. A reference potential (Vref) is applied to its non-inverting input terminal, and a voltage-current conversion resistor (Ra
) includes a negative feedback amplifier to which an input signal (Vin) is applied via the negative feedback amplifier, and a first and second A current mirror circuit is provided, and when the input signal (Vin) is at a lower level than the reference potential, (Vin-Vre) is output from the first current mirror.
f) By extracting a part of the feedback current determined by /Ra, an output corresponding to the input signal (Vin) is obtained, and when the input signal (Vin) is at a higher level than the reference potential, the Similarly from the second current mirror (Vin
By extracting a part of the feedback current determined by -Vref)/Ra, an output current corresponding to the input signal (Vin) is obtained. A rectifier circuit characterized by obtaining a rectified output corresponding to (Vin).