JPH0782043B2 - Rectifier circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rectifier circuit suitable for application to various electronic devices such as industrial measuring devices and low-frequency audio devices.

[Conventional technology]

Rectifier circuits are often used when a control signal is obtained in response to a change in the level of an analog signal or when the level is displayed. The simplest rectifier circuit utilizes the so-called diode rectification characteristics.

However, it is known to those skilled in the art that the diode is not an ideal element and the error becomes large especially when the input signal is very small.

In the "Practical design of analog circuit" (published on March 30, 1981, first edition, published by CQ Publishing Co., pp79-82), a rectifier circuit combining the above diode and operational amplifier is shown as an absolute value circuit. Has been done.

[Problems to be solved by the invention]

According to the study by the present inventors, in the rectifier circuit using the operational amplifier, unless the negative feedback circuit is configured, the input offset voltage of the operational amplifier is not compensated, and the rectifier circuit as shown in FIG. 3 and FIG. It has been found that there is an error in the characteristics. That is, the errors shown as A and B appear in the drawing.

Even if a negative feedback circuit is provided to eliminate the above error,
It is desirable to avoid the use of diodes because the current electronic devices are actually formed by semiconductor integrated circuits.

From this point of view, the inventors have studied to provide a rectifier circuit in which an error due to an input offset is reduced by providing a negative feedback circuit having a simple circuit configuration including an operational amplifier and a transistor, and completed the present invention.

It is an object of the present invention to provide a rectifier circuit having a simple circuit configuration and having a reduced error between an input signal and an output signal.

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

[Means for solving problems]

The following is a brief description of the outline of the typical invention disclosed in the present application.

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

[Action]

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 by the operation of the operational amplifier according to the negative feedback amount. Is achieved, and the object of the present invention is to obtain a rectifier circuit with a simple circuit configuration and a small error.

〔Example〕

A first embodiment of a rectifier circuit to which the present invention is applied will be described below 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 for explaining the circuit operation.

A feature of the present embodiment is that a negative feedback circuit having a simple circuit configuration including a current mirror circuit is provided in the negative feedback path of an operational amplifier to which an input signal is supplied, so that good rectification characteristics are obtained. .

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

The input signal Vin is applied to the inverting input terminal − via the input resistance Ra.
Is supplied.

The transistors Q ₁ and Q _{2 form} the first current mirror circuit in the present invention.

The transistors Q ₁₁ and Q _{12 form} the second current mirror circuit in the present invention.

The resistors R ₁ and R ₂ are adjusting resistors in the present invention, and the resistance ratio is such that the resistor R ₁ is 1 and the resistor R ₂ is 2.

If the input signal Vin is higher than the reference voltage Vref, the current Ia flows through the input resistance Ra. 1/2 · Ia flows through the transistor Q ₁ as a reference current. This current is drawn into the output side of the operational amplifier 1 through the resistor R ₂ .

On the other hand, the transistor Q ₂ also has a 1/2
-The current of Ia flows as an output signal, and the output voltage Va is obtained as the voltage drop of the output resistor R ₁₁ .

Next, when the input signal Vin is lower than the reference voltage Vref, the output current Ib corresponding to the level difference is obtained. A current of 1/2 · Ib flows as a reference current in the transistor Q ₁₂ , and further flows into the input resistor Ra via the resistor R ₁ .

It should be noted that the resistors R ₁ and R ₂ have the above resistance ratio, so that the reference current flowing through the transistors Q ₁ and Q ₁₂ is 1:
To be two. However, since the current Ia is the sum of the reference current and the output current of the first current mirror circuit, the current flowing through the input resistor Ra has the same amount of current.

Therefore, the amount of current Ia, 1/2 · Ib that flows through the input resistance Ra in both directions is determined by | Vin−Vref | / Ra. That is, the current ratio of the currents Ia and Ib is 1: 2, and this current ratio is made by the adjusting resistors R ₁ and R ₂ .

The reference current flowing through the transistors Q ₁ and Q ₁₂ 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.

The transistor Q ₁₁ is formed as a multi-collector.
This is because the reference current flowing through the transistor Q ₁₂ is twice as large as 1/2 · Ia, so that the current flowing through the output resistor R ₁₂ is the same as the current flowing through the output resistor R ₁₁ .

Therefore, as shown in FIG. 2, the input signal Vin is equal to the reference voltage Vre.
When the level changes around f, rectified rectified outputs as shown as Va and Vb are alternately obtained from the resistors R ₁₁ and R ₁₂ .

(1) By setting the non-inverting input terminal of the operational amplifier as a reference potential and comparing the input signal supplied to the inverting input terminal to drive the operational amplifier, the two current mirror circuits provided in the negative feedback circuit are By the action of being individually driven in response to the change in the polarity of the input signal, it is possible to obtain the effect of obtaining the rectified output half-wave rectified from the above-mentioned current mirror circuit 2.

(2) According to the above (1), since the error due to the offset on the input side of the operational amplifier is negatively fed back by the current mirror circuit, the output signal is corrected by the operational amplifier, and at least the error due to the offset is reduced. The effect of obtaining a rectified output is obtained.

(3) Since the rectifier circuit is composed of the operational amplifier and the circuit of 2, the circuit structure is simple, and the semiconductor integrated circuit can be easily manufactured.

(4) Due to the above (2), it is possible to obtain the effect of significantly improving the accuracy of industrial measuring instruments and the like.

Although the invention made by the present inventor has been specifically described above based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say.

For example, the resistors R ₁₁ and R ₁₂ may be replaced with a common load resistor. In this case, the rectified output is double-wave rectified.

It is desirable that the current mirror circuit of the second type has a circuit configuration in which the ratio of the reference current to the output current is more accurate, for example, a Wilson type. An example thereof is shown in FIG. This is because the current is accurately determined by Vin-Vref / Ra due to the high gain of the operational amplifier, but if the current mirror ratio of the current mirror interposed in the negative feedback path is different, this results in an offset generation factor.

〔The invention's effect〕

The effects obtained by the representative one of the inventions disclosed in the present application will be briefly described as follows.

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

[Brief description 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 input signal versus output signal for explaining the circuit operation of the rectifier circuit, and FIG. 3 is prior to the present invention. 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. is there. 1 ...... operational amplifier, Q ₁ ~Q ₁₂ ...... transistor, Vref ...
… Reference voltage, Ra …… Input resistance, R ₁ , R ₂ … Current adjustment resistors, Ia, Ib… Current, Va, Vb… Rectified output.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirofumi Ishii 1479 Kamimizumoto-cho, Kodaira-shi, Tokyo In-house Hitachi My Cross Computer Engineering Co., Ltd. Tobu Semiconductor Co., Ltd. (56) References Japanese Patent Publication Sho 60-41483 (JP, B2)

Claims (1)

[Claims] 1. An operational amplifier having a non-inverting input terminal set to a reference potential, and an input resistor (R connected between an analog signal input terminal and the inverting input terminal of the operational amplifier.
a) and the first and first currents provided in the middle of the feedback path between the output terminal and the inverting input terminal of the operational amplifier so that a current flows to either of the positive and negative sides of the reference potential of the analog signal. The first mirror is provided between the second current mirror circuit and the output terminal and the inverting input terminal of the operational amplifier.
One current of the second current mirror circuit between the first current adjusting resistor (R2) connected in series with one current element of the current mirror circuit and the output terminal and the inverting input terminal of the operational amplifier. A second current adjusting resistor (R1) connected in series with the element, wherein the first current adjusting resistor (R2) has a resistance value twice that of the second current adjusting resistor (R1). Is set so that a current of half the current of the second current mirror circuit flows through the first current mirror circuit, and the first current mirror circuit is A pair of transistors of the same conductivity type whose bases and emitters are connected in common, and when the analog signal is higher than the reference potential, 1/1 / th of the current flowing through the input resistance in each transistor
Two currents are configured so that one flows as a reference current toward the output terminal of the operational amplifier and the other flows as an output current, and the second current mirror circuit is the same as the transistor of the first current mirror circuit. Includes a pair of transistors of the same conductivity type of which the base and emitter are commonly connected to each other, and when the analog signal is lower than the reference potential, one transistor has a half of the current supplied from the operational amplifier. A current flows as a reference current toward the inverting input terminal, and the other transistor is a multi-collector transistor having two collectors, and half of the current from the operational amplifier flows into its emitter, and It is characterized in that 1/2 of the current flows from one of the collectors as the output current. Rectifier circuit.