JPH0463006A - Signal level detection circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a signal level detection circuit, and is suitable for application to, for example, a video tape recorder.

B. Summary of the Invention The present invention can simplify the overall configuration of a signal level detection circuit by detecting the signal level of an input signal by also using the detection circuit of the AGC circuit.

C. Prior Art Conventionally, in video tape recorders, AGC (au
The signal level of the reproduced signal is maintained at a predetermined value using a tomatic gain control circuit.

Further, in order to easily detect the state of just tracking, the signal level of the reproduced signal input to the ACC circuit can be detected by a signal level detection circuit.

That is, as shown in FIG.
In , the reproduced signal S□ is applied to the square law detection circuit 2, and the signal level of the reproduced signal 5IIF is detected here, and the detection result S is obtained. OA is output to a meter drive circuit (not shown).

As a result, the user can perform tracking adjustment according to the signal level of the reproduced signal, and can easily adjust to a state of just tracking.

Furthermore, in the video tape recorder 1, the playback signal S
The signal is applied to the variable gain amplifier circuit 6 of the IF@ACC circuit 4, and the output signal of the variable gain amplifier circuit 6 is output to the subsequent signal processing circuit.

In the AGC circuit 4, after the square law detection circuit 8 detects the output signal level of the variable gain amplifier circuit 6, the detection result S is detected. and the reference voltage ■□, the error amplification circuit 10
The comparison result is fed back to the variable gain amplifier circuit 6.

As a result, in the variable gain amplifier circuit 6, the gain is controlled so that the detection result of the square law detection circuit 8 becomes a constant value,
In this way, the signal level of the reproduced signal SIF is corrected to a predetermined value and processed by the subsequent signal processing circuit.

D Problems to be Solved by the Invention By the way, if the configuration of this type of signal level detection circuit could be simplified, the overall configuration of the video tape recorder could be simplified accordingly, which would be convenient.

The present invention has been made in consideration of the above points, and aims to propose a signal level detection circuit having a simpler configuration than the conventional one.

8 Means for Solving the Problems In order to solve the problems, in the present invention, the input signal SIF is controlled with a gain corresponding to the signal level of the control signal SCO.
A variable gain amplifier circuit 6 that amplifies and outputs the signal, a detection circuit 8 that detects the signal level of the output signal output from the variable gain amplifier circuit 6, and a detection result S0 of the detection circuit 8 and a predetermined reference value VIEF. Based on the comparison result of the control signal S
An error amplification circuit 10 that outputs COM and a control signal SC
o14 and a subtraction signal S of the detection result S0. Obtained LIT+,
A signal level detection signal S whose signal level changes according to the signal level of the input signal S0. Subtraction circuit 22 that outputs at
and be prepared.

A signal level detection signal S whose signal level changes according to the signal level of the input signal S0 by subtracting the detection result SKt of the F-effect detection circuit 8 and the control signal S Cog of the error amplifier circuit 10. E
By obtaining arl, the detection circuit 8 of the AGC circuit can also be used to detect the signal level of the human input signal SIF, and the overall configuration can be simplified accordingly.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, in which parts corresponding to those in FIG. 3 are given the same reference numerals, 20 indicates a video tape recorder as a whole;
In the subtraction circuit 22, the detection result 5I of the square-law detection circuit 8
The output signal S cos of the error amplifier circuit 10 is subtracted from IE and output to the meter drive circuit.

That is, as shown in FIG. 2, the detection result SKE of the square law detection circuit 8 is maintained at a predetermined signal level within the control range of the AGC circuit, but below the control range of the AGC circuit. , the signal level increases in proportion to the signal level of the reproduced signal SIF.

On the other hand, the output signal S COH of the error amplifier circuit 10 is held at a constant value below the control range of the AGC circuit, whereas within the control range of the AGC circuit, it is inversely proportional to the signal level of the reproduced signal S0. and the signal level decreases.

Therefore, the output signal S, is obtained from the detection result S□ via the subtraction circuit 22. 9, the signal level detection signal S whose signal level increases in proportion to the signal level of the reproduced signal SIF. You can get Ua.

Thereby, the signal level of the reproduced signal SIF can be detected by also using the square law detection circuit 8 of the AGC circuit.

Therefore, the signal levels of the reproduced signals S can be detected with a simple configuration in which only the subtraction circuit 22 is provided in place of the square law detection circuit 2.

In fact, since a square law detection circuit is constructed using a balanced modulator or the like, it is inevitable that the overall structure of the signal level detection circuit will be more complicated than when a subtraction circuit is used.

Therefore, according to this embodiment, the subtraction circuit 22 is provided in place of the square law detection circuit 2 to detect the signal level of the reproduced signal SIF, thereby simplifying the overall configuration of the video tape recorder. can.

In the above configuration, the signal level of the reproduced signal 5IIF is detected by the square law detection circuit 8 via the variable gain control circuit 6, and is maintained at a predetermined signal level based on the detection result.

On the other hand, in the signal level detection circuit, the output signal SCOi of the error amplifier circuit 10 is subtracted from the detection result S- of the square law detection circuit 8, so that the signal level is proportional to the signal level of the reproduced signal S□. The signal level detection signal S changes. tlTl can be obtained.

According to the above configuration, by detecting the signal level of the reproduced signal SIF by also using the square law detection circuit 8 of the AGC circuit, it is possible to obtain a signal level detection circuit having a simple configuration as a whole.

In the above-described embodiment, a case was described in which the output signal SCO of the error amplifier circuit 10 was subtracted from the detection result S□ of the square law detection circuit 8, but in the present invention, on the contrary, the output signal SCO and The detection result S0 may be subtracted from.

Furthermore, in the above embodiment, a case has been described in which the signal level of the output signal of the variable gain amplifier circuit is detected by using a square law detection circuit, but the detection circuit is not limited to this. , an envelope detection circuit using a diode, and various other detection circuits can be widely applied.

Furthermore, in the above-described embodiment, the case where the present invention is applied to a video tape recorder has been described, but the present invention is not limited to this. The present invention can be widely applied to signal level detection circuits that detect signal levels.

H Effects of the Invention As described above, according to the present invention, by detecting the signal level of the input signal by also using the detection circuit of the AGC circuit,
A signal level detection circuit having a simple configuration as a whole can be obtained.

video tape hook Figure 1

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a video tape recorder according to an embodiment of the present invention, FIG. 2 is a characteristic curve diagram for explaining its operation, and FIG. 3 is a block diagram showing a conventional video tape recorder. l, 20... Video tape recorder, 2.8.
... Square law detection circuit, 6 ... Variable gain amplification circuit, 10 ... Error amplification circuit, 22 ...
・Subtraction circuit. Input/output holding a Figure 2 → Input/output sign and bell

Claims (1)

[Scope of Claims] A variable gain amplifier circuit that amplifies and outputs an input signal with a gain that corresponds to the signal level of a control signal, and a detection circuit that detects the signal level of the output signal output from the variable gain amplifier circuit. and an error amplification circuit that outputs the control signal based on a comparison result between the detection result of the detection circuit and a predetermined reference value, and an error amplifier circuit that obtains a subtraction signal of the control signal and the detection result, and generates a signal of the input signal. 1. A signal level detection circuit comprising: a subtraction circuit that outputs a signal level detection signal whose signal level changes depending on the level.