JPS592229B2 - How to adjust a television receiver - Google Patents

Description

Detailed Description of the Invention The present invention provides an audio intermediate frequency amplification circuit (hereinafter referred to as SIF circuit) for a television receiver having an integrated circuit video intermediate frequency amplification circuit (hereinafter referred to as VIF circuit). The purpose of this invention is to prevent noise generated from the integrated circuit VIF circuit described above from entering the SIF circuit, and to facilitate adjustment of the SIF circuit.

FIG. 1 shows the configuration of a television receiver having an integrated VIF circuit.

However, only the necessary parts of the signal processing section will be described here. In the figure, 1 is a VIF circuit, which is composed of an amplifier 2, a bandpass filter 3, and a circuit 4 that performs amplification, demodulation, and demodulation amplification, and the frequencies it handles are as follows, taking Japan as an example:
57 ■ 0 to 4.5MH which is the vicinity of the signal and its demodulated output
It is z.

Further, 5 is an SIF circuit composed of a bandpass filter 6, an amplifier 7, and a wave detector 8, and its frequency is around 4.5×. In a television receiver having such a configuration, the bandpass filters 3 and 6 are adjusted at their respective frequencies, that is, the bandpass filter 3 is adjusted at around 57M[-I2, and the bandpass filter 6 is adjusted at around 4.5MH2. However, since the frequencies required for each adjustment are very far apart, the connection points for the signal sources for each adjustment are point b for VIF circuit 1 and point b for SIF circuit 5.
For example, it has to be placed at a separate location, such as point a.

Therefore, in the actual production process of television receivers, the configuration shown in Figure 2 is adopted, and the adjustment of the VIF circuit 1 and the SIF circuit 5 is performed by the same worker by switching the switch 9. There is.

Here, 21 is a signal source for adjusting the VIF circuit 1;
22 is a signal source for adjusting the SIF circuit 5, 23 is an oscilloscope for observing the adjusted waveform, and 24 is a noise generated from the VIF circuit 1 when adjusting the SIF circuit 5, the function of which will be described later. 25 is a power source for driving the solenoid coil 24. The solenoid coil 24 is constructed by inserting a plunger into a cylindrical coil through an elastic body. When a current flows through the coil, the plunger moves against the elastic force of the elastic body, and the current flow is reduced. When the supply is cut off, the force of the elastic body causes it to return to its original position. Here, a case will be considered in which the amplifier 2, demodulator 4, etc. of the VIF circuit 1 are constructed of integrated circuits.

As is well known, in an integrated circuit, the more pins (corresponding to 1 to 8 in Figure 3) that come out of the integrated circuit, the more the number of man-hours required, the price of the package, etc., and the higher the cost. Therefore, when designing an integrated circuit, we try to minimize the number of pins. An example of an integrated circuit designed in this manner is shown in FIG.

In the figure, the integrated circuit 4 constituting the amplification demodulation/demodulation amplification circuit has a high gain amplifier, a demodulator, and a demodulation output amplifier that are directly connected without being cut off by a capacitor. It also works as a high-gain amplifier from direct current to high frequency. Therefore, consider the case where the solenoid coil 24 is not provided in the VIF-SIF adjustment circuit having the configuration shown in FIG. Here, when the switch 9 is turned to the P side, the solenoid coil 24 is operated by being supplied with current through the contact S3.
A resistor R is connected between point C and the power supply Vcc. That is, the plunger moves when current is supplied to the coil from the power supply 25, and the tip metal body of the plunger, whose end is connected to the other end of the resistor R1 whose end is connected to the supply power Vcc, is connected to point C on the printed circuit board. do. At the same time, SIF
A signal source 22 and an oscilloscope 23 are connected to the circuit 5 . At this time, if the solenoid coil 24 is not present, the resistor R1 will not be connected between the point C and the power supply Vcc, so the noise generated from the integrated circuit 4 will be transmitted to the output terminal a of the IF circuit 1.
point, the noise is added to the SIF circuit 5, and the SIF
Adjustment of circuit 5 or interference with noise makes it impossible. SIF
The amplifier 7 of the circuit 5 is also a high gain amplifier and will be disturbed by even the slightest noise. This noise is generated inside the integrated circuit 4 and cannot be removed even if the input point e of the integrated circuit 4 is disconnected. Therefore, as shown in FIG. 2, the solenoid coil 24 is used.
A resistor R1 is connected between the point C and the supply voltage Vcc.

To explain the operation in this case using FIG. 3, the resistors R,
Due to this connection, the base bias of the transistor Q1 becomes high, and the transistor Q1 becomes saturated. Then, transistor Q2 is also saturated, and transistor Q3 is cut off. As a result, transistor Q4 is also cut off, transistor Q5 is saturated, and transistor Q6 is also saturated. Therefore, since transistor Q4 is cut off, the noise generated before transistor Q4 becomes a
Since transistors Q5 and Q6 are saturated, there is no amplification effect on the noise generated after transistor Q4, and the noise does not appear at point a, and even if it does appear, it is very small. , does not affect the adjustment of the SIF circuit 5 at all. Next, when the switch 9 is turned to the q side, the current in the solenoid coil 24 is cut off, and the resistance R1 becomes C.
The integrated circuit 4 returns to its original operation after moving away from the point and the power supply line Vcc, and the adjustment of the VIF circuit 1 is not hindered.

However, since this conventional method has a moving part called the solenoid coil 24, there are many failures of the solenoid coil 24.
Maintenance is difficult, and in addition, a separate power source for driving the solenoid coil 24 is required, and three circuits are required for the switch 9, and the switch 9 also needs to switch the high frequency signal source 22, so it must have good high frequency characteristics. There were various inconveniences.

Therefore, the present invention eliminates the above-mentioned disadvantages and provides VIF
This makes it possible to easily adjust the circuit and the SIF circuit without interfering with each other.

An embodiment of the present invention will be described below with reference to FIG.

To explain FIG. 4, a transistor QlOO is added from the outside to the emitter of the transistor Q6 in the integrated circuit 4, and the emitters are commonly connected to form a differential amplifier as shown in FIG. . The adjustment signal source 22 of the SIF circuit 5 is connected to the base of the transistor QlOO.
and its base bias can be turned on and off by contact S2 of switch 10. As is well known, in a differential amplifier, one transistor is cut off when the base bias of one transistor becomes higher than the base bias of the other transistor. In the opposite case, the other transistor is cut off. Using this principle, the base bias VB of transistor QlOO
lOOlR3V8lOO+VOO? By setting the transistor R3+R4 in the integrated circuit 4 to be higher than the base bias of the transistor Q6, when adjusting the SIF circuit 5, when the switch 10 is turned to the P side, the transistor QlO is set by the resistors R3 and R4.
Since a base bias is applied to O and the transistor Q6 in the integrated circuit 4 is cut off for the above-mentioned reason, the noise generated from within the integrated circuit 4 does not appear at point a, and this noise causes the SIF circuit 5 to Adjustment is not disturbed.

Next, when the switch 10 is turned to the q side, the transistor QlO
Since O is cut off and the transistor Q6 is activated, no problem occurs in the adjustment of the VIF circuit 1.

As explained above, according to the present invention, since there is no moving part such as a solenoid coil as in the past, there are fewer failures, there is no need to provide a separate power source for the solenoid coil, and furthermore, the F-SIF circuit can be adjusted. It also has the advantage that only two circuits are needed for the switch, which is extremely advantageous in practice.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of the configuration of a television receiver, Figure 2 is a circuit diagram showing the connections of conventional measuring instruments for adjusting the television receiver, and Figure 3 is a circuit diagram showing the connection state of each conventional measuring device used in the television receiver. FIG. 4 is a circuit diagram showing an example of the internal configuration of an integrated circuit according to the present invention, and FIG. 4 is a circuit diagram showing a method for adjusting a television receiver in an embodiment of the present invention. 1... Video intermediate frequency amplification circuit, 5...
Audio intermediate frequency amplification circuit, 10...Switch, 2
2...Signal source, 23...Oscilloscope, Q6, QlOO...Transistor, R3,
R4...Resistance.

Claims (1)

[Claims] 1. Each signal source is connected to an integrated video intermediate frequency amplification circuit whose output circuit has an emitter follower configuration and an audio intermediate frequency amplification circuit that is continuously connected to this video intermediate frequency amplification circuit. When adjusting each circuit, a transistor is connected to the emitter follower circuit to form a differential amplifier, a signal source for adjusting the audio intermediate frequency amplification circuit is connected to the base of this transistor, and the signal source for adjusting the audio intermediate frequency amplification circuit is connected to the base of the transistor. A method for adjusting a television receiver, comprising: a switch means for varying the base bias of a transistor; and the switch means controls the base bias of the transistor to turn on and off the emitter follower circuit.