JPS62248383A - Television sound demodulation circucit - Google Patents

Abstract

PURPOSE:To cancel a buzzing component in a detection sound signal by providing an adjusting circuit and an arithmetic circuit, adjusting the phase and the amplitude of automatic frequency (AFC) control signal, thereafter supplying to the arithmetic circuit and adding in a reversed polarity to a detecting sound signal from a sound detecting circuit or subtracting in the same phase. CONSTITUTION:The output signal of an LPF 12 is supplied to a phase adjusting device 13, herein, the phase is set to the buzzing component in the detecting sound signal of the sound detecting circuit 18, further, the buzzing component is set to the amplitude in a level adjusting device 14, and thereafter, the output signal is supplied to the arithmetic circuit 15. The detecting sound signal of the sound detecting circuit 18 has the phase adjusted through a phase adjusting device 16 and is supplied to the arithmetic circuit 15. In the arithmetic circuit 15, when an input AFC signal is adjusted so as to be the same phase as the bussing component in the FM detecting sound signal, the subtraction is performed and when it is adjusted so as to be the reversed phase to the buzzing component, the addition is performed. As a result of this, the sound signal in which the buzzing component is cancelled is taken out to an output terminal from arithmetic circuit 15.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a television audio demodulation circuit, and more particularly to a television audio demodulation circuit that receives and demodulates television audio signals using an intercarrier method.

BACKGROUND OF THE INVENTION FIG. 3 shows a block diagram of an example of a conventional audio demodulation circuit. In the figure, a television signal received by an antenna 1 is converted into an intermediate frequency signal by a tuner 2, and then
The signal is supplied to the video detection circuit 4 through the video IF amplifier circuit 3. Furthermore, an automatic frequency control circuit (AFC circuit) 5 and a low-pass filter (LPF) 6 are provided between the video IF amplifier circuit 3 and the tuner 2.

In general, in color receivers, the local oscillation frequency of the buyuna 2 is Changes need to be kept sufficiently small.

For this reason, an AFC circuit 5 is installed, and the AFC circuit 5 generates an AFC control terminal voltage (AFC signal) whose level changes in response to changes in the video intermediate frequency.
The signal is output to the tuner 2 via the P F 6, thereby suppressing the error in the locally generated frequency of the tuner 2 within a predetermined range (for example, within ±100kl-1z).

Next, a color video signal obtained by ΔM detection of the intermediate frequency signal by the video detection circuit 4 and a 4 to 5 MHz audio composed of a beat component (audio intercarrier signal) of the difference between the video carrier wave and the audio carrier wave are generated. The intermediate frequency signal is 4.5M
Only the color video signal is passed through the band 14 rejection filter (BEF) 7 of 1-12 and outputted to the output terminal 8, while only the near rear signal of the audio interface 4 is separated by the band pass filter (BPF) 9. .5Ml-(is supplied to the ZFM detection circuit 10, where it is FM detected, the audio signal is taken out, and is output to the output terminal 11.

Problems to be Solved by the Invention However, the phase modulation that occurs when amplitude modulation is performed on the transmitting side and the A in the video IF amplifier circuit 3 on the receiving side.
When a signal containing phase modulation generated by the GC circuit is input to the video detection circuit 4, it is affected by the phase modulation of the video carrier wave, causing a problem in that a puzzling sound is generated.

In this case, there is a problem in that the puzzling caused by phase modulation on the transmitting side cannot be improved on the receiving side.

SUMMARY OF THE INVENTION Therefore, the present invention aims to provide a television audio demodulation circuit which solves the above-mentioned problems by branching and extracting the output AFC signal of the FC circuit as a puzzling signal and calculating it with a detected audio signal. purpose.

Means for Solving the Problems The television audio demodulation circuit according to the present invention includes an adjustment circuit that adjusts the phase and amplitude of the AFC signal output from the AFC circuit, and an output signal of the adjustment circuit and the detected audio output of the audio detection circuit. It consists of an arithmetic circuit that performs addition or subtraction with signals.

The FC signal output from the operational AFC circuit has a waveform obtained by detecting the phase modulation of the video carrier wave on the transmitting side and the receiving side. This phase modulation of the video carrier wave is detected by an audio detection circuit and becomes a puzzle. Therefore, AFC No. 4:5 and Puzzle have similar waveforms.

After the phase and amplitude of the AFC signal are adjusted to minimize the puzzling component, the signal is supplied to an arithmetic circuit, where it is added with the opposite polarity or subtracted with the same phase as the detected audio signal from the audio detection circuit. As a result, the puzzle component in the detected audio signal is canceled by approximately 4 times.

Embodiment FIG. 1 shows a block diagram of an embodiment of a television audio detection circuit according to the present invention. In the figure, the same components as those in FIG. 3 are denoted by the same reference numerals, and the explanation thereof will be omitted. In FIG. 1, the output AFC signal of the AFC circuit 5 is branched into two, one of which is supplied to the LPF 6, and the other is supplied to the LPF 6.
PFl 2 is supplied.

Then, PF12 limits the band of the FC signal to
The low-pass filter that determines the power-puzzle band,
Phase El! ! ! 13.16, L/H/L/H rectifier 1
4 and the arithmetic circuit 15 constitute a puzzle canceller 17. Here, the output signal of the LPFI 2 is supplied to the phase adjuster 13, which adjusts the phase with the puzzle component (phase modulation signal component) in the detected audio signal of the audio detection circuit 18 consisting of the bandpass filter 9 and the FM detection circuit 10. The signal is approximately matched, and the amplitude is matched with the above-mentioned puzzle component by the level adjuster 14, and then the signal is supplied to the arithmetic circuit 15.

On the other hand, the detected audio signal of the audio detection circuit 18 has a phase adjustment of "1".
After the phase is adjusted via 16, the signal is supplied to the arithmetic circuit 15. In this way, in this embodiment, by providing phase adjusters at two locations, the arithmetic circuit 15 is configured to perform calculations for reducing puzzles with high precision. Further, the phase adjustment in this embodiment is performed, for example, in a factory or the like by an operator while looking at a measuring instrument.

The calculation path 15 is supplied with a phase-adjusted detected audio signal and a phase- and amplitude-adjusted AFC signal, respectively, and calculates (adds or subtracts) these input signals. Here, when the input AFC signal is adjusted to be approximately in phase with the puzzle component in the FM detected audio signal, it is subtracted, and when it is adjusted to be in opposite phase, it is added. , the puzzle component is roughly transmitted from the arithmetic circuit 15 to one output terminal.
The two celled audio signals are extracted.

Next, to explain the specific circuit of the present invention, FIG. 2 shows one embodiment of the specific circuit of the present invention.
Components that are the same as those in the figures are given the same reference numerals. In this embodiment, the video IF amplification circuit 3.degree. video detection circuit 4. AFC
Integrated circuit (IC) 2 as circuit 5 and FM detection circuit 10
0<For example, Toshiba model TA7680AP/TA76
81AP) is used. Above IC20
Includes bias circuit, FM detection circuit, attenuator, audio amplifier, video detection circuit, limiter, and AFT detection circuit.

It includes a video amplifier, noise inverter, AGC circuit, etc. Further, here, ■ to θ respectively indicate the bin numbers of ■C20.

The output intermediate frequency signal of the tuner 2 is supplied to the bins ■ and ■ of the IC 20, and the detected video signal output from the bin ■ is converted into an audio intercarrier signal via the BPF 9 and is supplied to the bins O and O. be done. Furthermore, IC2
The FC signal output from the bin O of 0 is output to the tuner 2 via the LPF 6. Also, the AFC signal is output from bin 0 of IC20, and the detection signal is output from bin ■. 11 signals are output.

Further, the LPF 12 includes a resistor R1 and a capacitor IC.
The phase adjuster 13 consists of a coil and capacitors C2 and C3, and the level adjuster 14 consists of at
ti amplifier 21. Consisting of a resistor R2 and a variable resistor Rv,
The adder circuit 22 corresponding to the arithmetic circuit 15 includes an operational amplifier 23 and resistors R3 and R4.

Here, bin O of IC20 is resistor R1 and capacitor C
1 in series to ground. The connection point between the resistor R1 and the capacitor C1 is grounded via a capacitor C2, and is also grounded via a coil and a capacitor C3 connected in series. The connection point between this coil and capacitor C3 is connected to the inverting input terminal of operational amplifier 21 via resistor R2. The non-inverting input terminal of the operational amplifier 21 is grounded, and a variable resistor Rv is connected between its output terminal and the connection point between the inverting input terminal and the resistor R2.

On the other hand, the output detected audio signal from the bin 2 of the IC 20 is supplied to the inverting input terminal of the operational amplifier 23 via the phase adjuster 16 and the resistor R3. Here, the connection point between the output terminal of the operational amplifier 21 and the variable resistor Rv is connected to C through the resistor R4.
It is connected to the connection point between the inverting input terminal of the f$ amplifier 2S23 and the resistor R3.

A non-inverting input terminal of the operational amplifier 23 is grounded, and an output terminal thereof is connected to the audio signal output terminal 24.

Here, the output AFC signal from bin O of IC20 is LP
Phase shift 1111m via F12! 13, where the predetermined phase is shifted. The amount of phase shift of this phase adjuster 13 is fixed, but may be variable. This circuit constant is set so that the phase of the above-mentioned puzzling component and the phase of the puzzling removal signal (ie, AFC signal) are matched. The level adjuster 14 is an inverting amplifier whose gain is variably controlled according to the resistance value of the variable resistor Rv, and after adjusting the output signal level of the phase adjuster 13 to be approximately equal to the puzzle component, the resistor R4 is The signal is output to the inverting input terminal of the operational amplifier 23 via the inverting input terminal.

In this way, the phase-adjusted detected audio signal and the phase- and level-adjusted AFC signal are combined in the adder circuit 22, and therefore, the puzzle component in the 1M detected audio signal sent to the output terminal 24 is substantially canceled out. The removed audio signal is output.

Note that the phase adjusters do not necessarily need to be provided at two locations, and only one of the phase adjusters "33 and 16" may be provided. A for control and puzzle detection
Although the FC circuit 5 is shared, there is a dedicated AFC for detecting the puzzle.
A separate circuit may be provided. Furthermore, it goes without saying that the connection order of the phase adjuster 13 and the level adjuster 14 may be changed.

Effects of the Invention As described above, according to the present invention, the output AFC of the AFC circuit
Since the signal is split into a puzzling reduction signal and the signal is taken out for calculation with the detected audio signal, it is possible to reduce the puzzling caused by phase modulation on the transmitting side and the receiving side.
It has features such as the ability to share circuits and the ability to configure the circuit configuration without making it too complicated.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a television audio demodulation circuit according to the present invention, FIG. 2 is a specific circuit diagram showing an embodiment of the present invention, and FIG. 3 is a conventional television audio demodulation circuit. This is a block system diagram showing an example of the circuit. 5... Automatic frequency control circuit (FG circuit), 12...
・Low pass filter (LPF), 13.16... Phase adjuster, 14... Level adjuster, 15... Arithmetic circuit, 1
7... Pazuki teacher, 18... Audio detection circuit,
19.24... Audio signal output terminal, 20... Integrated circuit (TC), 21.23... Operational amplifier, 22...
Korea circuit, C1-C8...capacitor,...coil, to R1/R4...resistance, Rv...variable resistor. Patent applicant: Victor Japan Co., Ltd. Figure 2

Claims (1)

[Claims] An intercarrier type television audio demodulation circuit includes an adjustment circuit that branches and takes out the output signal of an automatic frequency control circuit for controlling the local oscillation frequency of a tuner, and adjusts the phase and amplitude of the output signal, respectively; 1. A television audio demodulation circuit comprising: an arithmetic circuit that performs addition or subtraction between an output signal and a detected audio signal output from an audio detection circuit and outputs a detected audio signal with reduced puzzling.