JPS5927510B2 - Television receiver fault removal circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for eliminating interference between carrier waves such as a video carrier, a color subcarrier, and an audio carrier in a television receiver.

Television signals are transmitted from relay stations to each home in most areas, except around large cities. The radio waves from relay stations in rural areas and cities often do not have the P/s and modulation values specified, which prevents stable image reception. In particular, P/s is usually specified at 6 db, but if it is too low, it will cause bead interference of 92 degrees, and if it is too high, it will cause problems such as bass sound and deterioration of sound quality. For relay stations, broadcasting standards are not well managed, the reception may deviate from the specified values due to regional characteristics, and radio wave conditions may change from moment to moment due to weather conditions, etc. many. The present invention aims to eliminate such obstacles by providing a circuit for detecting P/s inside the receiver, and using this circuit to change the trap depth of the voice trap in response to the ever-changing P/8. , P/s deviate from the specified value, this deviation is automatically compensated, so that the television signal can be reproduced in good condition at all times. FIG. 1 is a block diagram showing the configuration of the present invention.

In the figure, 1 is a tuner that constitutes a television receiver, 2 is a trap circuit, 3 is a video intermediate frequency amplification circuit, and 4
5 is a video detection circuit, 5 is an AFC circuit, 6 is an audio intermediate frequency detection circuit, 7 is an audio detection circuit, 8 is a comparison circuit, and the circuits excluding the trap circuit 2 and comparison circuit 8 are those of a conventional television receiver. The same is true. The comparison circuit is a circuit that compares the levels of the video carrier and the audio carrier, and the video carrier for comparison is 58.75 for operating the AFC circuit 5.
The video intermediate frequency carrier signal of MH2 is taken out and used as one input of the comparison circuit 8, and as for the audio carrier, the 4.5MH2 bead signal after the audio intermediate frequency detection is taken out and used as the other input of the comparison circuit 8. The levels of both carriers are compared to detect the level difference, and the trap depth of the audio trap 2 is controlled using the detected voltage. FIG. 2 shows a specific example of a control circuit for the comparison circuit 8 and the trap circuit 2.

In the same figure, diode D1, resistor R1, capacitor C
1 constitutes a detection circuit for a 58.75MH2 carrier signal, and the diode D2, resistor R2, and capacitor C2 constitute 4.
It constitutes a detection circuit for the 5MH2 bead signal. The transistors Tr, Tr2 constitute a differential amplifier, the resistor R9, the diode D3, the resistor R1o, and the transistor Tr4 constitute a constant current source. The transistor Tr3 amplifies the detected output of the 4.5 MH2 bead signal and makes the levels of the signals sent to the differential amplifier equal. The resistors R, . . . and the capacitor C3 are filter circuits that determine the time constant for trap depth control. The transistor Tr5 uses an FET as an active resistor, and has an inductance L.
1. The trap depth of a bridge T-type trap composed of capacitors C4 and C5 and a transistor is controlled by the output of a differential amplifier. For example, when the video carrier is constant and the 4.5 MHz bead signal decreases, the base potential of the transistor Tr3 decreases and the collector potential of the transistor Tr3 increases.

Since the base potential of the transistor Trl remains unchanged, the collector potential of the transistor Tr2 decreases and the collector potential of the transistor Trl increases. Then FE
As the gate potential of TTr5 rises, the resistance between the source and drain becomes smaller, the depth of the trap becomes shallower, and the sound carrier increases. In this way, the depth of the audio trap is automatically adjusted in response to changes in the P/s ratio. In this way, by using the circuit of the present invention, areas where the P/s was lower than the specified value and a 920 KHz toto appeared,
Stable reception conditions can be obtained even in areas where P/s is higher than the specified value and bass noise is produced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention, and FIG. 2 is a circuit diagram showing an embodiment of the main part of the present invention. 1... Tuner, 2... Trap circuit, 3... Video intermediate frequency amplification circuit, 6...
- Audio intermediate frequency detection circuit, 8... Comparison circuit.

Claims (1)

[Claims] 1 Compare the levels of the video carrier P and audio carrier S of the received television signal, and if the ratio (P/S) deviates from a predetermined value, set the audio trap of the receiver according to the degree of the deviation. An interference removal circuit for a television receiver, characterized in that interference caused by mutual interference between carriers is removed by changing the depth.