JPH04192770A - Intermediate frequency signal processor - Google Patents

Abstract

PURPOSE:To suppress a sound signal so as not to change a frequency in other bands or not to attenuate the frequency by adding the sound signal component with a signal inverted the sound signal by means of an adder, eliminating these signals with each other. CONSTITUTION:A sound signal eliminating circuit 2 consists of a phase inversion amplifier 5 inverting and amplifying the phase of an output signal 30 of a tuner 12, a voice intermediate frequency SAW filter 6 extracting the sound signal component from the output signal of the phase inversion amplifier 5, a delaying device 7 outputting the output signal 30 of the intermediate frequency signal tuner 12 while delaying it by the delay time caused by the SAW filter 6 and an adder adding the output of the delaying device 7 with the output of the SAW filter 6. Thus, since the sound signal component of the intermediate frequency signal 30 are added with the inverted sound signal to cause them to be eliminated with each other, the change of frequency and the change of group delay characteristics in the other band caused by the sound signal can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an intermediate frequency signal processing device used in television receivers, video recorders, etc.

(Prior Art) In recent years, video equipment such as television receivers have a wider intermediate frequency amplification circuit due to double tuning of tuners, wider bandwidth of video SAW filters, and the like.

Figure 3 is an explanatory diagram of widening the band of this intermediate frequency amplification circuit.
In the case of a tuner, single tuning results in a narrow band and the frequency characteristics between the video carrier P and the audio carrier S become different near the center, whereas double tuning allows for a wide band. Therefore, the frequency characteristics can be made almost flat.

In addition, in the 5AW (surface acoustic wave) filter for video,
In the case of a narrow band, the signal level of the color subcarrier C is lower than that of the video signal component Vn by about 6 dB, and the signal level further decreases as the frequency component of the carrier color signal becomes higher.

On the other hand, by widening the band, the signal levels of the video signal component Vw and the color subcarrier C can be made almost the same.

In the case of a narrow band, the circuit can be relatively simple, but the effective bandwidth is narrow; in the case of a wide band, the effective bandwidth can be widened and the signal can be reproduced faithfully, but
The circuit becomes a little more complicated.

Furthermore, as the band becomes wider, the signal level of the audio carrier wave S in both the tuner and the video SAW filter also decreases. When the signal level of the audio carrier wave S becomes low, intermodulation is likely to occur in the preamplifier and demodulator, making it extremely difficult to demodulate the video.

Therefore, a trap circuit is generally used to attenuate this audio carrier wave S.

FIG. 4 is a circuit diagram of an example of this trap circuit. The trap circuit 20 includes capacitors C1 and C2 on the input side and output side, respectively, and a resistor R1 is connected in series between these capacitors C1 and C2. Capacitors C3 and C4 are connected in series between the input side of this resistor R1 and ground, capacitor C5 and variable coil L1 are connected in series between the output side of resistor R1 and ground, and the connection of capacitors C3 and C4 is connected in series. The connection point between the capacitor C5 and the variable coil L1 is short-circuited.

FIG. 5 shows the frequency 1, ? of this trap circuit 20. For external factors, the horizontal axis represents frequency and the vertical axis represents signal level. As is clear from this figure, the signal level has a characteristic that it is further attenuated only at frequencies near the audio carrier wave S.

In addition, since it is necessary to attenuate only the frequencies near the audio carrier wave S (=J), the Q of this trap circuit 20 must be made as high as possible.Also, in order to accurately set the frequency to be attenuated, adjustment is required. Since this is necessary, the trap circuit 20 uses a variable coil 1 to adjust the frequency, but it is also possible to use variable capacitors for the capacitors C1 to C5 and use the variable capacitors to adjust the frequency.

FIG. 6 is a configuration diagram of an example of a conventional intermediate frequency signal processing device in which the trap circuit 20 constitutes an audio signal removal circuit.

The conventional audio signal removal circuit 10 is composed of the trap circuit 20 described above, a tuner 12 is connected to the input side of the trap circuit 20, and a gain compensation preamplifier 13 is connected to the output side of the trap circuit 20.
, a video intermediate frequency 5AW (P, 5AW) filter 14, and a video detector (P.

DET) 15 are connected in series to form a video signal processing section 16 that generates video output. Moreover, the tuner 1
Further, on the output side of 2, there are a gain compensation preamp 7:/7'21, a 5AW (S, SΔW) filter for audio intermediate frequency 22, an audio intermediate frequency detector (SIFDET) 23, and an FM detector (FM DET) 24. An audio signal processing section 17 is formed which is connected in series and generates an audio output.

With such a configuration, the intermediate frequency signal 30, which is the output signal of the tuner 12, is processed by the fifth signal in the video signal processing section 16.
After passing through the trap circuit 20 having the frequency characteristics shown in the figure, it enters the gain compensation preamplifier 13, so the audio signal component near the audio carrier S is sufficiently attenuated, and the gain compensation preamplifier 13 and the video detector 15 Amplification and detection are performed without intermodulation.

On the other hand, since the intermediate frequency signal 30 before entering the trap circuit 20 is input to the audio signal processing section 17, the operation of audio demodulation is not affected by the trap circuit 20.

(Problems to be Solved by the Invention) However, as described above, in order to avoid damaging the waveform of the video signal from the video signal processing section 16, the trap circuit 20 must have a high Q. Therefore, Q
In order to increase the value, it is necessary to adjust the l-wrap circuit 20. However, even if the adjustment is made, the adjustment point may fluctuate due to temperature changes, since the coils and the like constituting the I-wrap circuit 20 have temperature characteristics. In addition, there is a possibility that the group delay characteristics of the frequency band near the adjustment point will be disturbed, and since the trap circuit 20 is accompanied by a gain loss, there is a possibility that the NF (noise figure) of the video signal processing section 16 will be deteriorated.

Therefore, it is an object of the present invention to provide an intermediate frequency signal that is less likely to cause changes in frequency characteristics or group delay characteristics in other bands, whose attenuation frequency is less affected by temperature changes, and whose NF is less likely to deteriorate. The purpose of this invention is to provide a processing device.

(Means for Solving the Problems) In order to solve the above problems, an intermediate frequency signal processing device according to the present invention includes a phase inversion amplifier that inverts and amplifies the phase of an intermediate frequency input signal, and an output of the phase inversion amplifier. a filter that extracts an audio signal component from a signal; a delay device that delays the intermediate frequency human horn signal by a delay time caused by the filter; and adds the output signal of this delay device and the output signal of the filter. The present invention is characterized in that it includes an audio signal removal circuit configured with an adder.

(Operation) The intermediate frequency input signal has its phase inverted by a phase inversion amplifier, and then passes through a filter to extract an audio signal component. On the other hand, the intermediate frequency input signal is also input to a delay device, and after delaying this intermediate frequency signal by the delay time caused by the filter, the delayed intermediate frequency signal and the audio signal component extracted from the filter are Added by an adder.

Then, a video intermediate frequency signal from which the audio signal component has been removed is obtained as the output of this adder.

(Example) Embodiments of the present invention will be described below based on the accompanying drawings.

FIG. 1 is a configuration diagram of an intermediate frequency signal processing device according to the present invention,
FIG. 2 is an explanatory diagram of the same operation.

In FIG. 1, an intermediate frequency signal processing device 1 according to the present invention includes an audio signal removal circuit 2, a video signal processing section 3 that processes a video signal out of the output of this audio signal removal circuit 2, and this audio signal removal circuit. 2, and a tuner 12 that inputs an intermediate frequency signal 3o to the audio signal removal circuit 2.

Furthermore, the audio signal removal circuit 2 includes a phase inversion amplifier 5 that inverts and amplifies the phase of the output signal 30 of the tuner 12, and an audio intermediate frequency amplifier that extracts an audio signal component from the output signal of the phase inversion amplifier 5. The SAW filter 6 and the output signal 30 of the intermediate frequency signal tuner 12 are
It is comprised of a delay device 7 that delays the output by the delay time generated by the W filter 6, and an adder 8 that adds the output of this delay device 7 and the output of the SAW filter 6.

The video signal processing unit 3 includes a conventional gain compensation preamplifier 13 that amplifies the output of the adder 8, a conventional video intermediate frequency SAW filter 14 that extracts video signal components, and a conventional video signal processor that demodulates the video signal. It is composed of a wave detector 15. Further, the audio signal processing section 4 includes a conventional SIF detector 23 and a conventional FM detector 24, which demodulate the audio signal from the output of the SAW filter 6.

Next, the operation will be explained with reference to FIG.

FIG. 2 consists of (A), (B), and (C), and the left side of each figure shows the frequency characteristics, and the right side of each figure shows the signal waveform.

FIG. 2A shows the output j signal of the delay device 7.

That is, this output signal is delayed by the delay time generated by the SAW filter 6 and output as the intermediate frequency signal 30.
It is. This signal has a frequency characteristic including an audio signal component centered on the audio carrier wave S and a video signal component centered on the video carrier wave P, as shown in the left diagram. Also, as shown in the figure on the right, the waveform of this intermediate frequency signal 30 is the same as the video carrier wave 1).
(frequency 58.75 MHz) and audio carrier wave S (frequency - 〇 - 54.25 MHz) are close to each other, so the frequency difference between P and S (beat frequency) is 4.5 M I (P is modulated by z. The waveform will be similar to that of the previous example.

FIG. 2B shows the output signal of the SAW filter 6.

That is, this output signal includes only an audio signal component centered on the carrier wave S, and the phase of this audio signal component is inverted by the phase inverting amplifier 5.

FIG. 2C shows the output signal of the adder 8.

That is, this output signal is a signal obtained by adding (Δ) and (I3) in the same figure, and as shown in (C) in the same figure, the above-mentioned audio signal component, that is, the above-mentioned P and S, is obtained from the signal in (A) in the same figure. The signal is obtained by removing the frequency difference (beat signal) of 4.5 MHz.

It should be noted that the output of the adder 8 and the output of the audio intermediate frequency SΔW filter 6 are processed in the same manner as in the conventional example, so a description thereof will be omitted.

In addition, the amount of attenuation of the audio signal component conventionally required is 16 to 20 d.
Since it is about B, if the variation in the gain of the phase inversion amplifier 5 is designed to be about ±1 dB with respect to the level of the audio carrier wave S of the intermediate frequency signal 30, it is possible to eliminate the adjustment.

For example, when a 100 dBμ signal is applied across a 75 Ω resistor, the generated voltage is O, IV, and similarly 9
When a 9 dBμ signal is applied, the generated voltage is approximately 0,
It becomes 089V. If these signals cancel each other out, then at the input ratio, residual carrier=20X1og((0,1-0,089)10.1)=
The amount of attenuation is approximately -19.2 dB, and the required amount of attenuation can be obtained.

As described above, according to the present invention, the audio signal component can be removed from the intermediate frequency signal 30 similarly to the conventional trap circuit 20.

Furthermore, since the adder 8 is used to add and cancel the audio signal component of the intermediate frequency signal 30 and the inverted audio signal component, changes in frequency and group delay characteristics are not caused to other bands. The frequency to be attenuated is less likely to fluctuate due to temperature changes, and the NF is less likely to deteriorate. Furthermore, if a predetermined amount of attenuation is anticipated and designed in advance, the effort of adjustment can be almost eliminated.

(Effects of the Invention) As explained above, according to the intermediate frequency signal processing device according to the present invention, the adder adds an audio signal component and a signal obtained by inverting this audio signal component, so that the signals cancel each other out. , the frequency that changes or attenuates the frequency in other bands is less likely to fluctuate due to temperature, and the N
It also reduces the possibility of worsening F.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an intermediate frequency signal processing device according to the present invention,
Fig. 2 is an explanatory diagram of the same operation, Fig. 3 is an explanatory diagram of widening the band of the intermediate frequency amplification circuit, Fig. 4 is a circuit diagram of an example of a conventional trap circuit, and Fig. 5 is a frequency characteristic of the same L/wrap circuit. 6 are configuration diagrams of an example of the same intermediate frequency signal processing device. DESCRIPTION OF SYMBOLS 1...Intermediate frequency signal processing device, 2...Audio signal removal circuit, 5...Phase inversion amplifier, 6...SAW filter for audio intermediate frequency, 7...Delay device, 8...Addition vessel.

Claims (1)

[Claims] a phase inversion amplifier that inverts and amplifies the phase of an intermediate frequency input signal; a filter that extracts an audio signal component from the output signal of the phase inversion amplifier; and a filter that delays the intermediate frequency input signal by a delay time generated by the filter. 1. An intermediate frequency signal processing device for video equipment, comprising an audio signal removal circuit including a delay device that outputs an output signal, and an adder that adds an output signal of the delay device and an output signal of the filter.