JPH03121677A - Television receiver - Google Patents

Abstract

PURPOSE:To prevent the complicated manufacture process by using a phase shift coil of an audio FM detector to adjust a filter built-in an integrated circuit. CONSTITUTION:A coil 10 connected to an IC pin leading to an audio FM detector 7 as an externally mounted coil is used to adjust the phase shift. When the phase shift is adjusted, since a mean level of a DC voltage resulting from smoothing a detected output is changed, when the DC voltage is applied to a band pass filter 6, the characteristic of the band pass filter 6 is adjusted. Thus, it is not required to provide any special adjustment means for a trap circuit 3 and the band pass filter 6 and the adjustment is implemented in common procedure as the coil 10 for phase shift adjustment. Thus, number of adjusting points in the manufacture process is decreased and the complicated manufacture process is avoided.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a TV (television) receiver that detects video signals and audio signals, and in particular, is capable of automatically adjusting filter characteristics. Regarding television receivers.

(b) Conventional technology The video and audio detection circuits of TV receivers require a plurality of filters, and some have built-in filters in an IC (integrated circuit). However, since the values of resistors and capacitors within the IC vary, it is difficult to accurately determine the filter characteristics of the filter, and the filter inside the IC is generally adjusted from outside the IC. $2
figure! i. A circuit diagram showing such a TV receiver, VIP (
The VIP signal from the video intermediate frequency (video intermediate frequency) amplifier (1) is detected by the video detector (2) and becomes a video signal. The video signal is transmitted to the trap circuit (3) through a 5IF (4,5 MHz).
After the audio intermediate frequency) signal is removed, it is led out of the IC via an external pin (4>) of the IC.

Also, the SIF signal from the SIF amplifier (5) is applied to a bandpass filter (6) to generate an SIF signal of 4 and 5 MHz.
Only the signal is extracted and applied to the audio detector (7) and F
M detection is performed. The detected audio signal is sent to the external pin (8)
It is led out to the outside of the IC via. The audio detector (7) is
It consists of a phase shifter and a multiplier, and it is necessary to phase shift the input signal by 90 degrees.The filter (10) and capacitor (11) placed outside the IC by an external pin (9) , used for phase shifting operation.

Through an external pin (12), a volume (13) placed outside the IC is connected to a trap circuit (3) and a bandpass filter (6) inside the IC, thereby controlling the pass characteristics of the two filters. control is performed.

Therefore, according to the circuit shown in FIG. 2, the filter inside the IC can be controlled to have desired filter characteristics.

(c) Problems to be Solved by the Invention However, in the circuit shown in FIG. 2, adjustment work for the volume (13) is required in the manufacturing process of the device, resulting in complicated work.

(d) Means for Solving the Problems The present invention has been made in view of the above points, and includes an audio FM detector for FM detecting an audio FM signal, and an audio FM detector for extracting a video signal or an audio signal. A filter is built into the integrated circuit, and a phase shifting means for performing a phase shifting operation of the audio FM detector and a smoothing means for smoothing the detection output of the audio FM detector are externally attached to the integrated circuit. The filter is arranged so that the passage characteristic of the filter is controlled according to the smoothed output of the smoothing means.

(E) Function According to the present invention, the amount of phase shift is adjusted by adjusting the coil connected to the audio FM detector as an external part of the IC. When the amount of phase shift is adjusted, the average level of the DC voltage obtained by smoothing the detected output changes, so by applying the DC voltage to the filter, the characteristics of the filter can be adjusted.

(f) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention, (14)
consists of a resistor (15) installed inside the IC and a capacitor (17) placed outside the IC via an external pin (16), and smoothes the audio detection output of the audio detector (7).
This is a smoothing circuit that applies smoothed output as a control signal to the trap circuit (3) and bandpass filter (6).

In FIG. 1, circuit elements that are the same as those in FIG. 2 are denoted by the same reference numerals, and explanations thereof will be omitted.

Next, the operation will be explained. The audio detector (7) is a rectangular FM detector, and its detection characteristics are as shown in FIG. In Fig. 3, r indicates 4°5 MHz, and the audio signal is detected around this frequency.
When the detected output at this time is smoothed by the smoothing circuit (14) in Fig. 1, the smoothed output is .

becomes. The coil that determines the amount of phase shift from this state 10)
When the value of is changed, the amount of phase shift changes, and the figure 8 curve in FIG. 3 moves in parallel. Therefore, the value of the smoothed output v0 described above changes and is applied to the trap circuit (3) and the bandpass filter (6). Therefore, by adjusting the values of the coil (10), the two filter characteristics can be controlled to desired values. At this time, the DC level of the audio detection output of the audio detector (7) fluctuates, but there is no problem because the DC component of the audio detection output is generally removed by the coupling capacitor (18) at the subsequent stage.

Therefore, according to the circuit shown in FIG. 1, there is no need to provide special adjustment means for the trap circuit (3) and the bandpass filter (6), and the coil (10) for adjusting the phase shift amount can also be used. You can make adjustments.

Now, the above explanation was about a so-called separate (split) carrier type audio demodulation method, but the present invention is not limited to this, and may be used in an intercarrier type. FIG. 4 shows an embodiment in that case, and since the configuration and operation are almost the same as those in FIG. 1, explanations will be omitted.

(G) Effects of the Invention As described above, according to the present invention, the filter built in the integrated circuit can be adjusted by using the phase shifting coil of the audio FM detector. Therefore, the number of adjustment points in the manufacturing process can be reduced, and the manufacturing process can be prevented from becoming complicated.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a circuit diagram showing a conventional TV receiver, FIG. 3 is a characteristic diagram for explaining FIG. 1, and FIG. 4 is a circuit diagram showing another embodiment of the present invention. <3>...Trough, B circuit, (6)...Band pass filter, (7)...Audio detector, (10)...
・Coil, (14)...Smoothing circuit. Figure 1

Claims (3)

[Claims] (1) an audio FM detector that performs FM detection on an audio FM signal;
A filter provided for extracting a video signal or an audio signal is built into an integrated circuit, and a phase shifting means for performing a phase shifting operation of the audio FM detector and a detection output of the audio FM detector are incorporated. A television receiver characterized in that a smoothing means for smoothing is disposed externally to the integrated circuit, and a pass characteristic of the filter is controlled according to a smoothed output of the smoothing means. (2) The television receiver according to claim 1, wherein the filter is a trap circuit that removes an audio signal from a video detection output signal. (3) The television receiver according to claim 1, wherein the filter is a bandpass filter that removes unnecessary components from the output signal of the audio IF amplifier.