JPH0454716A - Agc circuit - Google Patents

Abstract

PURPOSE:To attain fast convergence at the time of starting an input without loss of a response speed by providing a means setting an initial value of an integration means which applies comparison and integration to the output of a detection means in the AGC circuit. CONSTITUTION:A detector 2 detects the envelope of an output of the AGC circuit, the detected output is subject to comparison and integration to adjust the gain of a variable gain amplifier 1, the AGC circuit is provided with an initial value setting means 4 setting an initial value of the output of the integration device 3 to set an initial value, then the signal convergence at the time of starting input is enhanced.

Description

[Detailed description of the invention] [Industrial application field] The present invention is directed to AGC (Automatic Galn Co., Ltd.)
ntral) circuit.

[Conventional technology]

An example of a conventional analog type AGC circuit is shown in FIG. 5 and will be described.

Conventional analog AGC circuit, 1! In order to reduce the steady-state residual, the AGC circuit is configured with a first-order closed loop. As shown in Figure 5, the AGC circuit detects the magnitude of the output amplitude of the variable gain amplifier in order to monitor the output amplitude of one circuit. Has 1vF2. An integrator 3 is connected to the output side of the detector 2, which compares a preset reference voltage with the output of the detector 2 and integrates the difference.The output of the integrator 3 has a gain controlled by voltage control. It is connected to a variable gain amplifier 1 instead. Here, the variable gain amplifier 1 is an amplifier whose gain can be varied by an external control voltage, and a signal to be stably amplified by MuGC operation is inputted to this amplifier. The output of the variable gain amplifier 1 is the output of this AGC circuit), and the feedback loop is composed of a detector 2 and an integrator 3.

The detector 2 constitutes a detection means for detecting the envelope of the output of the circuit, the integrator @3 constitutes an integration means for comparing and integrating the output of this detection means, and the variable gain amplifier 1 constitutes an integration means for comparing and integrating the output of this detection means. It is configured so that the gain is controlled by the output.

The operation of the GC circuit shown in FIG. 5 will now be described.

First, when an AC input is supplied to this 500 circuit, it is amplified by the variable gain amplifier 1 and a friend AC output is sent out. The detector 2 detects this AC output and outputs a DC output proportional to the magnitude of the envelope of the AC output.

Next, the integral a3 compares this DC output with a reference voltage corresponding to the target value of the acoustic output amplitude and integrates the difference. The variable gain amplifier 1 has its gain controlled by the output of the integrator 3.

For example, when the transform output amplitude is larger than the target value, the detector 2 outputs nine DC outputs corresponding to the magnitude of the amplitude. Integrator is3 compares this DC output voltage with a reference voltage, and continues to integrate the difference in the direction of decreasing the gain of variable gain amplifier 1. The output amplitude of the variable gain amplifier 1 gradually decreases by K. Further, the DC output voltage of the wave detector 2 also becomes a multiplier, and when it becomes equal to the reference voltage, the integrating operation of the integrator 3 is stopped and the output amplitude of the variable gain amplifier 1 is stabilized.

[Problem to be solved by the invention]

In such a conventional GC circuit, when there is no input signal for a long time, for example, before the tape is started in a magnetic tape device, the output of the integrator 3 is almost the same as the output of the detector 20, so the variable gain amplifier 1 is If the circuit is saturated so that the gain is maximized, and then an input of an appropriate size is input, the output amplitude of the circuit will be excessive, and it will take a long time for the output amplitude to reach the target value. fC, this time is determined by the integrator 30 time constant. At the same time, the incoming GC
The required response speed of the circuit is similarly determined by the integral 630 time constant.

As mentioned above, in the conventional MGC circuit, this trade-off determination is a problem in systems where the target data arrival time is faster than the MGC circuit response speed, and the response required for the 50C circuit is The problem was that it hindered speed.

[Means to solve the problem]

The GC circuit of the present invention is composed of a detection means for detecting the envelope of the output of the circuit, an integration means for comparing and integrating the output of the detection means, and a variable gain amplifier whose gain is controlled by the output of the integration means. This GC circuit is provided with an initial value setting means for setting an output above the initial value of the integrating means.

[Effect]

In the present F14, fast convergence is provided at the start of inputting an input signal without interfering with the response speed required of the GC circuit.

〔Example〕

Embodiments of the present invention will be described in detail below based on the drawings.

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

In FIG. 1, the same reference numerals as in FIG. It constitutes an initial value setting means for setting an initial value.

And this initial value setting section 4 is the integral formula 7 formula %) The value ct is forcibly set when 1=0.

FIG. 2 is a circuit diagram showing a specific example of the structure of the integrator 3 and the initial value setting section 4. As shown in FIG.

In FIG. 2, parts that are the same as those in FIG. 1 are given the same reference numerals and explanations will be omitted. 5 is an operational amplifier. and,
By configuring negative feedback with a capacitor 6, it becomes an integrator. 1 is resistance.

-10,000, the initial value setting section 4 is a transistor 8. Resistance 10.1
This can be easily realized by using a switch 44 and a resistor 9, each consisting of a switch 44 and a resistor 9.

Next, assuming that the present invention is applied to an AGC circuit such as a magnetic tape device, the operation will be explained with reference to FIG. 3, which is a time chart showing the operation of the embodiment of the present invention.

First, FIG. 3-F shows the tape running state. In accordance with this, a reproduced signal is generated as shown in FIG. 3, Q)J.

FIG. 3 to shows the output of the detector 2. Before the tape starts running, the output of the detector 2 (shown in Figure 3 (C)) is zero, so the output of the integrator 3 maximizes the gain of the variable gain amplifier 1. The saturated aspect can be clearly seen in Figure 443 (dl).

Next, when the tape starts running, as shown in FIG. decreases at a speed determined by a time constant determined by the capacitor 6 and resistor 7, and reaches approximately the visual value at which the reproduced signal appears.

As a result, the amplified and reproduced signals are stably amplified from the start of input.

Furthermore, if it is required to set the initial value accurately, a comparator 12 is provided in the initial value setting section 4 as shown in FIG.
The integrator 3 is configured to continue charging until the target voltage is reached.

In this case, the target voltage source 13 is controlled by the control signal e (third
When the voltage (see Figure 1) is at a low level, a voltage sufficiently higher than the target voltage is output, and when the voltage is at a high level, the target voltage is output, and the same operation as in the embodiment shown in Figure 2 is performed. Note that in FIG. 4, the same reference numerals as in FIG. 2 indicate the same parts.

〔Effect of the invention〕

As explained above, in the present invention, since the AGC circuit is provided with an initial value setting means, it is possible to achieve fast convergence at the start of inputting an input signal without impeding the response speed originally required of the AGC circuit. This has the effect of making it possible to realize a highly accurate AGC circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the AGC circuit according to the present invention, FIG. 2 is a circuit diagram showing a specific configuration example of an integrator and an initial value setting section, and the third WJ shows the operation of the embodiment of the present invention. FIG. 4 is a circuit diagram showing another example of the configuration of the initial value setting section, and FIG. 5 is a block diagram showing an example of a conventional AGC circuit. 1...Variable gain amplifier, 2...Detector, 3...
... Integrator, 4... Initial value setting section. Figure 1

Claims (1)

[Claims] In an AGC circuit comprising a detection means for detecting an envelope of the output of the circuit, an integration means for comparing and integrating the output of the detection means, and a variable gain amplifier whose gain is controlled by the output of the integration means, the integration means An AGC circuit comprising an initial value setting means for setting an initial value of an output of the AGC circuit.