JPS59182681A - Television receiver - Google Patents

Abstract

PURPOSE:To attain ease of circuit integration by detecting noise component of a color TV signal and controlling each AGC circuit of video and sound system so as to realize the common use of a noise cancellor circuit. CONSTITUTION:A color TV composite video signal VS from a detector 12 is amplified 13 in a video signal processing system A, and its output signal VS' is applied to a buffer amplifier 14 and the noise cancellor circuit 15. The circuit 15 detects the noise component in the signal VS', its detected output expands the operating time of an AGC detecting circuit 16, the AGC output controls the gain of video image IFA11a-11c and the AGC output controls the gain of the RFA2 via an RF AGC circuit 17. Further, an output Sd of the detector 22 is applied to an amplifier 23 and an AGC detecting circuit 24 in the sound signal processing system B. Then, the output of the circuit 15 is given also to the circuit 24, and the AGC output controls the gain of the sound IFA21a-21c.

Description

[Detailed description of the invention] The present invention relates to a television receiver.

Currently, as a method for television receivers, a method has been proposed in which video signals and audio signals are individually detected and amplified from a stage subsequent to a high-frequency amplifier circuit.

In this system, AGO circuits are provided for the video signal processing system and the audio signal processing system, and each AGO circuit has a noise canceller circuit.

According to studies conducted by the inventors of the present application, it has been found that each noise canceller circuit is provided with a capacitor for canceling noise components, which is a cause of high costs. That is, there is now a tendency for most of various electronic circuits to be integrated into semiconductor integrated circuits (IC), and television receivers are no exception to this trend. When the AGO circuit or the noise canceller circuit is integrated into an IC, the capacitor is required, and at the same time, an external connection terminal for connecting the capacitor must be provided separately.

In other words, in order to achieve the same purpose as the video signal and the audio signal, two capacitors are required as external components, and therefore two external connection terminals are required. Having a large number of external connection terminals not only increases the chip size of the semiconductor integrated circuit, but also becomes an obstacle in providing multifunctions to the IC.

Therefore, it is an object of the present invention to provide a TenVision receiver that uses a single noise canceler circuit for both a video signal processing system and an audio signal processing system, and is suitable for semiconductor integrated circuit implementation.

An embodiment of a television receiver to which the present invention is applied will be described below with reference to FIGS. 1 to 3.

First, describe the overall circuit operation with respect to FIG.

Among the radio waves received by the receiving antenna 1, a desired broadcasting frequency f is transmitted to the high frequency amplifier circuit 21/j.

is selected and supplied to the mixing circuit 3. Local oscillation circuit 4
always shoots a local frequency sieve that is, for example, 58.75 MHz higher than the frequency of the video carrier included in the broadcast frequency f 1 and supplies it to the mixing circuit 3 . In the mixing circuit 4, frequency mixing is performed between the broadcast frequency 15 and the local frequency f□, and a frequency signal f of the difference between the two frequencies is generated. is obtained. The video signal filter 5 receives the frequency signal f. The analogy is frequency 5
A video intermediate frequency signal vIF of 8.75 MHz is obtained. The audio signal filter 6 receives the frequency signal f. For example, frequency 5
A 4.25 MHz audio intermediate frequency signal SIF is obtained.

The video frequency signal VIF is supplied to the first stage intermediate frequency circuit 11a of the video signal filter. The audio frequency signal SIF is supplied to the first stage intermediate frequency circuit 21a of the audio signal processing system B. It is assumed that the circuits constituting the video signal processing system A and the audio signal processing system B are integrated circuits using the same semiconductor substrate, although not particularly shown in the drawings.

The following will be described in order from video signal processing system A: 11a,
1lb and 11c are video intermediate frequency circuits; 1. The output signal is supplied to a video detector 12.

The video detector 12 outputs a color composite video signal V5 including horizontal and vertical synchronization signals and a luminance signal, and is supplied to the video amplification circuit 13 at the next stage.

In the video amplification circuit 13, the color TV composite video signal v5 is voltage amplified, and the output signal V,/ having a waveform as shown in FIG. supplied to In addition,
The output signal of the buffer amplifier 14 is supplied to a delay line, a synchronous separation circuit, and a nine-color demodulation circuit (none of which are shown).

Noise canceller circuit 15. The AGO detection circuit 16 will be described in detail with reference to FIG. 2, but when a noise component N is included in the color television signal (2), /, this is detected and the video intermediate frequency circuit 11a is activated.

11b, to control the gain of LIC. Note that the noise component N is generated by power supply noise, ignition noise generated while the automobile is running, and the like. I(,
The F-AGO circuit 17 controls the gain of the high frequency amplifier circuit 2 using the detection output of the AGO detection circuit 16.

Next, to describe the circuit operation of the audio signal processing system B, audio intermediate frequency signals with a frequency of 54.25 MHz output from the audio intermediate frequency circuits 21a, 21b, and 21c are supplied to the AM detection circuit 22 at the next stage. .

The detection output Sd has substantially the same waveform as the color television signal V,/, and is supplied to the amplifier 23 and the AGO detection circuit 24. The output signal of the amplifier 23 is supplied to a limiter (not shown), and the output of the limiter is supplied to an FM detection circuit (9, not shown).

Then, an audio signal is obtained from the FM detection circuit.

The AGO detection circuit 24, together with the noise canceller 15 and the like, will be described in detail with reference to FIG. 2. A
The detected output V o/ of the GO detection circuit 24 causes the audio intermediate frequency circuits 21a and 21b.

21c gain control is performed.

Next, noise canceller 15. AGO detection circuit 16.
The circuit operation of No. 24 will now be described.

The base of the transistor Q constituting the noise canceller 15 is maintained at a predetermined voltage level by the reference voltage VREF1. Further, the base of the transistor Q2+ constituting the AGO detection circuit 16 is connected to the reference voltage VRE.
It is maintained at a predetermined voltage novel by F□. However, the voltage levels of both are set to vRF:F2 > vRBFI, and the voltage level of REF2 is as shown in Figure 3.
Approximately equal to the synchronous peak value. Furthermore, the base of the transistor QII constituting the AGO circuit 24 is also connected to the reference voltage VREF.
3 is determined in the same way as the base voltage VREF□.

First, a case will be described in which the color television signal V, / contains no noise component. The transistor Q2 is turned off and the transistor Q is turned on. A current flows from the +vcc power supply to the ground line via the resistor R and transistor Q1. Then, since no current flows through the collector of transistor Q2 and no voltage appears at point A, capacitor O1 is not charged.

On the other hand, the transistor Q2+y Q22 performs so-called peak value type AGO detection. When the horizontal synchronizing signal H8 is supplied to the base of the transistor Q22 every 1H of one horizontal scanning period, the transistor Q22 is turned off and the transistor Q21 is turned off.
operates in the on state. During the retrace period, current flows through resistor R8, and the voltage drop causes transistor Q2 to
4 operates in the on state. By the detection diode D1,
Voltage drop V of resistor R7. is obtained as the AGO output, but since the capacitor C2 is provided, the voltage V. The waveform becomes as shown in FIG. 3(B), and no sudden increase in level appears.

Voltage ■. That is, gain control is performed for each video intermediate frequency circuit 11a, 1lb, and 11c by the AGO output.

Next, the circuit operation when a noise component N is generated in the color television signal 8' will be described. In this case, the voltage level of the color TV composite video signal V, / is the reference voltage ■R) iF+
decreases more than Transistor Q2 operates in the on state, and the voltage level at point A changes due to the voltage drop of resistor R6 ■9
increases rapidly as shown in Figure 3 (q).As a result, the resistance R
9. Charging current flows to capacitor 01 via external connection terminal 1. This charging current causes the voltage level at one end of capacitor C8, in other words, the voltage level at terminal 1 to be V
B gradually rises as shown in FIG. This charging characteristic is determined by the resistor R,l and the capacitor 010 time constant.

On the other hand, the voltage ■□ turns on the transistor Q3 and forcibly lowers the base voltage of the transistor Q2s. Therefore, transistor Ql operates in an off state, and transistors Qt++ and Q2t are both in an off state. As a result, when noise occurs, transistor Q2
A large current does not flow through the terminal 1, and the voltage ① does not rise suddenly.

Transistor Q21? Q2□ is in the off state, but the voltage ■ is caused by capacitor C2. hardly changes. Then, the AGO operation is not abruptly performed due to the noise component, and the normal AGO operation is performed after the noise disappears.

On the other hand, if the resistor R0, capacitor O, . When supplied to the detection circuit 16, during this large pulse width tN, the noise canceller circuit 15 activates the video AGO detection circuit 1.
6 to a low level, and as a result, the gain of the high frequency amplification circuit 2 and the video intermediate frequency amplification circuit 11a, 1l
b.

11c is controlled to an extremely large value, proper AGO operation is not performed, and a so-called AGO lockout phenomenon occurs.

On the other hand, in this embodiment, the time constant circuits R9, O
Because of the arrangement of I and the detection transistor Q4, when a pulse component N with a large pulse width tN is supplied, the time constant 4 circuit R (1g
The voltage VB of Ol is the base of the detection transistor Q'a.
When the emitter-to-emitter forward threshold voltage is exceeded, the detection transistor Q4 is turned on.

Then, transistor Q3 is turned off again, and normal circuit operation is resumed. That is, the transistor Q3 is on for one hour as shown in FIG. Long outs are prevented.

Next, the AGO operation regarding audio signals will be described.

The AGO circuit 24 has the same circuit configuration as the AGO circuit 16 described above. Further, the reference power supplies VR1, 3 and the audio signal vd have a relationship as described in the AGO circuit 16.

Therefore, the same circuit operation is performed when there is no noise component in the audio signal Sd or when a noise component occurs, and the voltage ■ is the same as the voltage ■o. ' is obtained as the AGO output via the detection diode D2.

And the voltage V. ', the intermediate frequency circuit 21a.

Gain control of 21b and 21c is performed.

Note that when a noise component appears in the audio signal S, it appears at the same timing as the noise component N described above. And the transistor Qu e Q10 + Q10 + Q,
u is the transistor Q2.u in the AGO circuit 16. .

An operation corresponding to Q22 t Q23 + Q24 is performed, and voltage Vo' is obtained as the AGO output. Resistance RA
, RA' are capacitors 02. This is for the discharge of O.

As a result of the above-described circuit operation, the only external component required for the noise canceller is the capacitor C1 (and only one external connection terminal is required).

Moreover, compared to installing two sets of noise cancellers, the circuit configuration is simpler and requires fewer circuit components.
When integrated into an IC, the degree of integration increases.

Therefore, not only can the video signal processing system and the audio signal processing system be configured on the same semiconductor substrate, but also other circuits that provide multiple functions can be provided.

In the embodiment described above, the noise component N of the color television signal V, / is detected;
, / is wider than the frequency band of the audio signal Sd. In other words, if the noise component of the color television signal V,/ is detected, especially the audio signal Vd
In addition to detecting the noise component N of , it is possible to perform both noise canceling operations at the same time. In this case, the noise component generated in the high frequency region of the color television signal vs' may not be detected. Therefore,
The circuit configuration shown in this example is more excellent as a noise canceller.

Note that the video signal filter 5. The audio signal filter 6 may be replaced by a so-called composite SAW filter (surface acoustic wave filter).

As described above, although the television receiver to which the present invention is applied has an extremely simple circuit configuration, it is capable of detecting noise components contained in a video signal, and has a stable AGO for the video signal processing system and the audio signal processing system. can be made to perform an action.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the main parts of a television receiver showing an embodiment of the present invention, and FIG. 2 is a block diagram of a noise canceller, a video AGO circuit, and an audio AGO circuit showing an embodiment of the present invention.
FIG. 3 is a circuit diagram of a GO circuit. A... Video signal processing system block, B... Audio signal processing system block, 15... Noise canceller circuit, 1
6... Video AGO detection circuit, 24... Audio AGO circuit, Q 1t Q2 + Qs + Q4 + Qll
I Q, +2? Q131Q+4・Q21・Q22
*Q23 *Q24- Transistor, 0,
...Capacitor, ■5'...Color TV signal, S
,...audio signal, Vo, vo'...AGO output voltage. Figure 2 Figure 3

Claims (1)

[Claims] 1. In a television receiver in which a video signal processing system and an audio signal processing system are separately provided after the frequency mixing circuit,
a video AGO circuit that obtains an AGO output from a color television signal; an audio AGO circuit that obtains an AGO output from an audio signal;
Detects noise components occurring in the color TV signal above,
A television receiver each comprising a noise canceller circuit that commonly controls the video signal AGO circuit and the audio signal AGOu path to be inactive for a predetermined period of time when a noise component is detected.