JPH0236607A - Limiter circuit - Google Patents

Abstract

PURPOSE:To obtain excellent accuracy, frequency characteristic and distortion characteristic by adopting a feedback type utilizing a differential amplifier for a limiter circuit and employing a transistor(TR) to constitute its feedback circuit. CONSTITUTION:The feedback type limiter circuit consists of a differential amplifier 1 and a feedback TR 3 for limiter. Then the TR 3 for limiter is completely turned off in the region where no limiter is applied. Thus, the original signal is not distorted and the deterioration in the frequency characteristic is not caused. Since the difference from a setting voltage is compressed to a fraction of loop gain of the feedback circuit in the limiter region, it is possible to apply limiting up to a high frequency when a high gain is applied to the feedback circuit at a broad band. Thus, the limiter circuit with excellent accuracy, distortion characteristic and frequency characteristic is obtained as a simple circuit against a signal with a small amplitude and a wide band such as a picture signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a limiter circuit for image signals, etc., and particularly to a limiter circuit suitable for circuits that require good accuracy, frequency characteristics, and distortion characteristics.

[Conventional technology]

For example, the conventional limiter circuit is described in "OP Amplifier Circuit Design J
As discussed in Mao Okamura, published by CQ Publishing (1985), pages 179 to 183, diodes have a wide uncertainty region (approximately 0.7 V) and poor distortion characteristics. In order to improve this, circuits using OP amplifiers have been devised.

[Problem to be solved by the invention]

2. In the conventional limiter circuit using an OP amplifier, its frequency characteristics are limited by the frequency characteristics of the OP amplifier in the linear region where the limiter is not applied, and the characteristics of the OP amplifier are limited in the limiter region where the limiter is applied. Therefore, there was a problem in that the limiter was not applied to signals of several LOOKHz or more.

SUMMARY OF THE INVENTION An object of the present invention is to provide a limiter circuit which can apply a highly accurate limiter to a wide band (4 MHz) signal such as an image signal and can provide low distortion characteristics in a non-limiter region.

[Means to solve the problem]

The above purpose is to make the limiter circuit a feedback type using a differential amplifier, to widen the band by configuring the feedback circuit using transistors, and to completely turn off the limiter transistor element in the non-limiter region.
This is achieved by a limiter circuit with reduced distortion.

[For production]

The above limiter circuit consists of a feedback limiter circuit consisting of a differential amplifier and a feedback transistor for the limiter, and in the region where the limiter is not applied, the original signal is distorted by completely turning off the 1-transistor for the limiter. In addition to not causing any deterioration of frequency characteristics,
Furthermore, in the limiter region, the difference from the set voltage is compressed to 1, which is the loop gain of the feedback circuit, so if the feedback circuit is made to have a high gain over a wide band, it is possible to apply a limiter to high frequencies.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 is a configuration diagram of a lower limiter circuit showing an embodiment of the limiter circuit according to the present invention. In Figure 1, Vi
n is an input terminal, and Vout is an output terminal.

V ref is the limiter setting voltage terminal, Vcc, Vee
is a power supply terminal, Tri, Tr2 is an NPN transistor for amplification, Tr3 is a feedback PNP transistor for limiter,
1 is a differential amplifier (comparison amplifier).

In the above configuration, the transistor Tr of the differential amplifier 1
When the base voltage of i is higher than the limiter setting voltage Vref, the limiter transistor Tr3 is completely ○FFL.
, the output voltage Vout is expressed by the following equation.

Vout=　　　　　　　　　　　VinR, +R.

This output voltage Vout operates linearly with respect to the input voltage Vin. Further, when the base voltage of the transistor Tri of the differential amplifier 1 is lower than the set voltage V ref, the output voltage Vout is expressed by the following equation.

Vout=Vref-(Vref-・Vin)/βR
1+R where β is the loop gain of the feedback circuit. Therefore β
When Vout is large, the output voltage Vout becomes the following equation.

V out '4 V ref This output voltage Vout shows the limiter characteristics of the set voltage Vref.

FIGS. 2(a) and 2(b) are characteristic diagrams showing the measured values of the circuit when R1=R2 in FIG. 1, and FIG. 2(a) shows the static characteristics.

FIG. 2(b) shows the distortion characteristics. In Figure 2 (σ),
Input voltage Vin (when set voltage Vref=-0,5V
The measured values of the output voltage Vout(V) with respect to V) are shown, and the limit characteristics in the limit region are good.

Furthermore, the linear characteristics in the linear region are also good up to high frequencies.

Further, in FIG. 2(b), the set voltage V ref =-
0.5V, input voltage Vin=I Vp-p, 2M
) Tz, the input offset voltage V off (V )
Quadratic for.

The third-order distortion attenuation (dB) is shown, and the distortion characteristics in the linear region are good.

FIG. 3 is a block diagram of an upper limiter circuit showing another embodiment of the limiter circuit according to the present invention. In FIG. 3, the same reference numerals as in FIG. 1 indicate corresponding parts, Tri and Tr2 are amplifying PNP transistors, and Tr3 is a limiter feedback NPN transistor.

In the above configuration, the upper limiter characteristic similar to the lower limiter characteristic in FIG. 1 can be changed.

〔Effect of the invention〕

According to the present invention, a limiter circuit with good accuracy, distortion characteristics, and frequency characteristics can be replaced with a simple circuit for small amplitude, wideband signals such as image signals.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a lower limiter circuit showing an embodiment of the limiter circuit according to the present invention, and FIG. 2(a). (b) is a static characteristic and distortion characteristic diagram of FIG. 1, and FIG. 3 is a configuration diagram of an upper limiter circuit showing another embodiment of the limiter circuit according to the present invention. 1... Differential amplifier (comparison amplifier) r Tr3...
Feedback transistor for limiter, Vin...input terminal,
Vout...Output terminal, Vref...Limiter setting voltage terminal.

Claims (1)

[Claims] 1. In a feedback limiter circuit using a differential amplifier,
A limiter circuit characterized in that a feedback limiter circuit is constructed from a differential amplifier and a limiter feedback transistor.