JPH05176246A - Image stabilization circuit - Google Patents

Abstract

PURPOSE:To make noise unremarkable by extracting a difference between an IF-AGC and an RF-AGC voltage as an output voltage to control a picture quality correction circuit thereby correcting the picture quality in matching with an electric field strength of an antenna input signal. CONSTITUTION:An RF-AGC voltage (reverse) and an IF-AGC voltage (forward) are led from an AGC amplifier circuit 8 of a television signal processing through an RF-AGC voltage detection circuit 13 and an IF-AGC voltage detection circuit 14. Then voltage level adjustment circuits 15, 16 adjust the voltages into a prescribed level and the result is inputted as inputs 1, 2 of a difference detection circuit 17 and a level difference is extracted as an output. The output is switched by a diode D1 and fed to a picture quality correction circuit 11 adjusting the contrast of the video signal provided in the IC3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image stabilizing circuit in an electronic device such as a television receiver or a VTR equipped with a television tuner.

[0002]

2. Description of the Related Art A block diagram of a conventional device is shown in FIG. An input signal coming from the antenna is tuned by a tuner 1, converted into a video intermediate frequency (hereinafter referred to as VIF) signal, amplified by a VIF preamplifier 2, and VIF amplified by a television signal processing IC 3. It is led to the circuit 4.

The video signal amplified by the VIF amplification circuit 4 is detected by the VIF detection circuit 5 to become a video signal,
The video signal is amplified by the video amplifier circuit 6 and then led to the video amplifier circuit (not shown) at the next stage.

The AGC circuit is an AGC detection circuit 7 for detecting an AGC voltage from the video signal of the video amplification circuit 6.
And an AGC amplifier circuit 8 for DC-amplifying the detection voltage from the AGC detector circuit 7, and the IF-AGC voltage derived from the AGC amplifier circuit 8 is fed back to the VIF amplifier circuit 4 and the VIF amplifier circuit 4 outputs the IF-AGC voltage. The automatic gain control is performed, and the RF-AGC voltage from the AGC amplifier circuit 8 is led to the outside of the television signal processing IC 3 and supplied to the RF circuit of the tuner 1 to perform the automatic gain control of the RF circuit. .. 9 is a countermeasure for hunting by the AGC circuit,
It is a time constant circuit for slowing the response speed of the AGC circuit to the extent that hunting does not occur.

A typical example of the relationship between the AGC voltage and the electric field strength of the antenna input signal in the above AGC circuit is shown in FIG. Therefore, in general, AGC control is S / N
In order to perform (noise figure) without deteriorating, the gain control of only the VIF amplifier circuit 4 is performed by the IF-AGC voltage while the electric field strength of the input signal is relatively weak.
When the electric field strength of the input signal becomes stronger, the gain of the RF circuit is controlled by the RF-AGC voltage.
The switching of the gain control is performed when the electric field strength of the antenna input signal is about 60 dbμ. As a result, the gain of the video detection output with respect to the electric field strength of the antenna input signal is as shown in FIG.

On the other hand, as shown in FIG. 8, the image quality is corrected by adjusting the DC voltage source 10 from the outside and using the image quality correction circuit 11 to adjust the voltage.
This is done by adjusting the high frequency band around 3 MHz. FIG. 6 shows this state. When the DC voltage of the DC voltage source 10 is lower than the reference voltage, the gain is lowered and the image quality is soft, and when it is higher than the reference voltage, the gain is increased and the image quality is hard. Become.

[0007]

In the above conventional apparatus, the image quality is adjusted by manually adjusting the semi-fixed DC voltage from the outside, and the adjustment according to the electric field strength of the antenna input signal is performed. Not done. Therefore, there is a problem that the back noise is conspicuous when the electric field strength of the antenna input signal is weak.

Further, since the AGC circuit has a time constant circuit, its response speed becomes slow. Therefore, at the moment when the antenna input suddenly changes from no signal to a strong input signal, RF-
Since the AGC circuit operates at the maximum sensitivity, there are problems that the dynamic range of the RF amplifier circuit is exceeded and the output is distorted, the AFT circuit malfunctions, and synchronization is momentarily disturbed.

[0009]

In order to solve the above problems, the present invention is an RF-AGC for detecting an RF-AGC voltage.
Voltage detection circuit and IF-A for detecting IF-AGC voltage
GC voltage detection circuit and RF-from both voltage detection circuits
A configuration in which a difference voltage detection circuit that detects a difference voltage between the AGC voltage and the IF-AGC voltage and an image quality correction circuit that adjusts the contrast of a video signal controlled by the difference voltage derived from the difference voltage detection circuit are provided. To do.

Furthermore, the above IF-A in a weak electric field
A time constant circuit that reduces the time constant of the RF-AGC voltage detection circuit based on the GC voltage is provided to suppress image distortion in the transition period when a signal with a strong electric field is received from no signal. Use the same configuration.

[0011]

According to the above construction, IF-AGC and RF-
IF-AGC and RF obtained from AGC voltage detection circuit
-The AGC voltage is led to the difference voltage detection circuit, the difference between the two voltages is taken out as the output voltage, and the image quality correction circuit is controlled by this output voltage, so that the image quality can be corrected according to the electric field strength of the antenna input signal. It is possible to make noise inconspicuous.

Further, when the weak electric field strength of the antenna input which cannot perform AGC control as shown in FIG. 3, the time constant of the RF-AGC voltage detection circuit is reduced, so that the response speed of the AGC circuit becomes faster. Therefore, even if a signal having a strong electric field strength is suddenly input from a signal having no signal or a signal having a weak electric field strength, the output waveform is not distorted because the response speed is high.

[0013]

FIG. 1 is a block diagram of an embodiment of the present invention,
The parts corresponding to the conventional example shown in FIG. 8 are designated by the same reference numerals, and the description thereof will be omitted. In FIG. 1, a circuit 12 surrounded by a dashed line
Is a main part of the image stabilizing circuit of the present invention. In the figure, 13 is an RF-AGC voltage detection circuit that detects the RF-AGC voltage derived from the AGC amplification circuit 8, and 14 is an IF- that detects the IF-AGC voltage derived from the AGC amplification circuit 8.
AGC voltage detection circuit, 15 and 16 are the above-mentioned RF-AGC
And a voltage level adjusting circuit for adjusting the level of the output voltage from the IF-AGC voltage detecting circuits 13 and 14.

Reference numeral 17 is a difference voltage detection circuit which is composed of an OP amplifier or a differential amplifier which takes the respective outputs of the voltage level adjusting circuits 15 and 16 as an input signal and takes out the level difference between the both input signals as an output. The output of the differential voltage detection circuit 17 is passed through the diode D1 and further through the inversion circuit 18, and the image quality correction circuit 1 in the television signal processing IC 3 is
Is led to 1.

On the other hand, 19 is a discrimination circuit provided between the output terminal of the differential voltage detection circuit 17 and the output terminal of the DC voltage source 10, and the discrimination circuit 19 has resistors R1 and R as shown in FIG.
2 and a transistor Q1. The transistor Q1 is turned on at the same timing as the diode D2 provided between the DC voltage source 10 and the image quality correction circuit 11, and is turned on at the same voltage as the voltage Vf at which the diode D2 is turned on. Set to.

Reference numeral 20 is a discrimination circuit which is controlled by the output of the voltage level adjusting circuit 16 and switches between the RF-AGC circuit and the time constant circuit 21.

The embodiment of the present invention is configured as described above, and its operation will be described below. From the AGC amplifier circuit 8 of the television signal processing IC 3 via the RF-AGC voltage detection circuit 13 and the IF-AGC voltage detection circuit 14,
An RF-AGC voltage (reverse type) and an IF-AGC voltage (forward type) as shown in FIG. 3 are derived.

The RF-AGC voltage and the IF-AGC voltage are adjusted to predetermined levels by the voltage level adjusting circuits 15 and 16, respectively, and the input 1 and the input of the differential voltage detecting circuit 17 composed of an OP amplifier or a differential amplifier are adjusted. Entered as 2.

The differential voltage detection circuit 17 takes out the level difference between the input 1 and the input 2 as an output. The output level characteristic is as shown in FIG. That is, the differential voltage detection circuit 1
The output of 7 becomes a negative voltage when the electric field strength of the antenna input signal becomes strong, and becomes a positive voltage when the electric field strength of the antenna input signal becomes weak, with the inversion point as a boundary. The electric field strength at the inversion point can be arbitrarily set by the voltage level adjusting circuits 15 and 16.

The output of the differential voltage detection circuit 17 is guided to the diode D1 and switched, and is supplied to the image quality correction circuit 11 provided in the television signal processing IC3. That is, as shown in FIG. 4, when the electric field strength of the antenna input signal is stronger than the inversion point, the differential voltage detection circuit 17
Output becomes negative (at the time of strong input), and the diode D1 is cut off. When the electric field strength of the antenna input signal is weaker than the inversion point, the output of the differential voltage detection circuit 17 becomes positive (at the time of weak input), the diode D1 conducts, and the output of the differential voltage detection circuit 17 is sent to the next inversion circuit 18. It is guided and further supplied to the image quality correction circuit 11.

The inversion circuit 18 inverts the input voltage and outputs the result. The relationship between the input signal and the output signal is shown in FIG. The inverting circuit 18 is a television signal processing IC.
As shown in FIG. 6, the characteristic of the image quality correction circuit 11 provided in the circuit 3 is that the gain increases as the DC voltage increases,
This is a circuit required when the image quality changes from soft to hard, and is not necessary when the image quality correction circuit 11 has a characteristic opposite to that shown in FIG.

On the other hand, the output of the differential voltage detection circuit 17 is also supplied to the discrimination circuit 19. The determination circuit 19 is operated by the user when the automatic correction circuit operates, and the DC voltage source 1
The DC voltage supplied from 0 to the image quality correction circuit 11 in the television signal processing IC 3 via the diode D2 is cut off. The output voltage of the differential voltage detection circuit 17 is input to the transistor Q1 via the voltage adjusting resistors R1 and R2 shown in FIG.

The transistor Q1 is the diode D described above.
Since it conducts at the same voltage as the voltage Vf at which 2 conducts, the transistor Q1 also conducts at the same timing as the diode D2. When the transistor Q1 becomes conductive, the DC voltage source 10
The DC voltage from is led to ground through the collector and emitter of the transistor Q1 and becomes approximately 0V, and as a result, the diode D2 is cut off.

That is, the voltage supplied to the image quality correction circuit 11 is normally given through the diode D2, but when the antenna input signal becomes a weak electric field, the automatic correction operates and the voltage difference detection circuit 17 passes through the diode D1. The voltage of the level according to the electric field strength of the antenna input signal from is supplied,
The diode D2 is cut off.

The AGC voltage is detected as described above, and linear automatic image quality correction according to the electric field strength of the input signal can be performed. That is, when the input signal becomes weaker, the image quality becomes softer so that the noise of the image becomes inconspicuous.

On the other hand, the input 2 from the IF-AGC voltage detection circuit 14 is input to the discrimination circuit 20. This discrimination circuit 20
Is composed of a switching circuit, and the time constant circuit 21
And the RF-AGC circuit are opened and closed. The switching timing of the determination circuit 20 is as shown in FIG. When the electric field strength of the antenna input signal is weak and the range in which AGC control cannot be performed, the discrimination circuit 20 including the switching circuit is turned off so that the time constant circuit 21 is not connected to the RF-AGC circuit.

Next, the electric field strength of the antenna input signal is AG
When it becomes strong within the C control range, the discrimination circuit 20 constituted by the switching circuit is turned on, and the time constant circuit 2
1 and the RF-AGC circuit are closed loop. Since the connection between the time constant circuit 21 and the RF-AGC circuit is thus selected according to the electric field strength of the antenna input signal, even if the antenna input signal is switched from no signal (weak electric field input signal) to a strong input signal, Since the response speed of the RF-AGC circuit is fast, the output of the tuner 1 is not distorted.

[0028]

Since the present invention is constructed as described above,
Since the image quality is linearly corrected according to the electric field strength of the antenna input signal, the image noise can be made inconspicuous. Further, even when the antenna input signal is switched from no signal or weak signal to a strong signal rapidly, the IF output derived from the tuner is not distorted, and it is possible to prevent synchronization disturbance.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of a main part of an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between an electric field strength of an antenna input signal and an AGC voltage.

FIG. 4 is a diagram showing output characteristics of the detection circuit in FIG.

5 is a diagram showing the characteristics of the input voltage of the inverting circuit in FIG.

6 is a diagram showing characteristics of the image quality correction circuit in FIG.

7 is a diagram showing switching timing characteristics of the determination circuit in FIG.

FIG. 8 is a configuration diagram of a conventional example.

FIG. 9 is an operation explanatory diagram of FIG. 8;

[Explanation of symbols]

 11 image quality correction circuit 13 RF-AGC voltage detection circuit 14 IF-AGC voltage detection circuit 17 differential voltage detection circuit 20 discrimination circuit 21 time constant circuit

Claims (2)

[Claims] 1. An RF-AGC for detecting an RF-AGC voltage.
Voltage detection circuit and IF-A for detecting IF-AGC voltage
GC voltage detection circuit and RF-from both voltage detection circuits
A difference voltage detection circuit that detects a difference voltage between the AGC voltage and the IF-AGC voltage, and an image quality correction circuit that is controlled by the difference voltage derived from the difference voltage detection circuit and that adjusts the contrast of the video signal are provided. Characteristic image stabilization circuit. 2. An RF-AGC for detecting an RF-AGC voltage.
Voltage detection circuit and IF-A for detecting IF-AGC voltage
GC voltage detection circuit and RF-from both voltage detection circuits
A differential voltage detection circuit that detects a differential voltage between the AGC voltage and the IF-AGC voltage, an image quality correction circuit that adjusts the contrast of a video signal controlled by the differential voltage derived from the differential voltage detection circuit, and a weak electric field A time constant circuit that reduces the time constant of the RF-AGC voltage detection circuit based on the IF-AGC voltage is provided, and image distortion in a transition period when a signal with a strong electric field is received from no signal is provided. An image stabilizing circuit characterized by suppressing