JPH078016B2 - Horizontal AFC circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a horizontal AFC circuit used in a television receiver.

[Conventional technology]

Conventionally, the circuit shown in FIG. 4 has been widely used as a horizontal AFC circuit of this type. In FIG. 4, the base of the NPN transistor 6 is connected to the horizontal synchronizing signal input terminal 20 to perform switching operation by the horizontal synchronizing signal, the emitter is connected to the GND through the resistor 12, and the collector is NPN.
It is connected to the emitter of the transistor 5. The base of the NPN transistor 5 is the collector of the NPN transistor 7.
It is connected to the constant voltage source 17 through the base short circuit and the resistor 11, and the collector of the NPN transistor 5 is connected to the common emitter of the NPN transistor 3 and the NPN transistor 4. The emitter of the NPN transistor 7 is G through the resistor 13.
Connected to ND. The base of the NPN transistor 3 is connected to the flyback pulse input terminal 19, and the collector is
The collector of the PNP transistor 1, the GND through the capacitor 15, and the constant voltage source 17 through the capacitor 14 and the resistor 8.
And is connected to the horizontal AFC output terminal 18. The emitter of the PNP transistor 1 is connected to the constant voltage source 17 through the resistor 9, and the base is connected to the collector-base short circuit of the PNP transistor 2 and the collector of the NPN transistor 4. The emitter of the PNP transistor 2 is connected to the constant voltage source 17 through the resistor 10. The base of the NPN transistor 4 is connected to the constant voltage source 16. In FIG. 4, a horizontal oscillator (not shown) whose oscillation frequency is controlled by a voltage is connected to the next stage of the horizontal AFC output terminal 18, and the phase of the flyback pulse is output by the output of this horizontal oscillator. Changes, the conventional horizontal AFC circuit operates so that the horizontal AFC loop is applied at the timing as shown in FIG. here,
The resistor 8 and the capacitors 14 and 15 operate as a time constant circuit that determines the operation response time of the horizontal AFC circuit.

[Problems to be solved by the invention]

Since the conventional horizontal AFC circuit described above is provided with only one horizontal AFC time constant circuit, there is a drawback that a good horizontal AFC operation can be obtained only at a narrow horizontal oscillation frequency. Especially when a receiver is commonly used as a terminal of an information processing device, the horizontal frequency of a standard TV is 15.75KHZ, whereas when used as a terminal requiring high resolution, the horizontal frequency of 31.5KHZ is doubled. Therefore, using the same time constant was very problematic in terms of high stabilization of the horizontal AFC.

In contrast to the above-described conventional horizontal AFC circuit, the present invention has an original content that the optimum horizontal AFC time constant can be automatically selected for each of two or more horizontal oscillation frequencies.

[Means for solving problems]

In the horizontal AFC circuit of the present invention, a flyback pulse is applied to the base of a differential amplifier in which the emitters of two transistors are commonly connected, and a horizontal synchronization signal is applied to the bases of switching transistors in cascade connection to the common emitter. A horizontal AFC circuit in which an active load and a time constant circuit are connected to the output end of a dynamic amplifier, and a plurality of combinations of the differential amplifier, the active load and the time constant circuit are provided, and each of the plurality of differential amplifiers is commonly used. The switching transistor is controlled between the emitter and the switching transistor by an output of a frequency discriminating circuit that converts the frequency of the horizontal synchronizing signal into a voltage, and one of the plurality of differential amplifiers and the switching transistor are controlled according to the frequency of the horizontal synchronizing signal. And a comparator circuit for connecting the outputs of the plurality of differential amplifiers to the bases. Characterized in that the data and the emitter to extract the horizontal AFC output from the common emitter of the emitter follower which is connected in common, respectively.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. NP
The base of the N-transistor 6 is connected to the horizontal sync signal input terminal 20, the emitter is connected to the GND through the resistor 12,
The collector is connected to the emitter of NPN transistor 5. The base of the NPN transistor 5 is the NPN transistor 7
Constant voltage source through the collector, base short and resistor 11
17 and the collector of NPN transistor 5 is connected to the common emitter of NPN transistor 26 and NPN transistor 27. The emitter of the NPN transistor 7 has a resistor 1
Connected to GND through 3. The base of the NPN transistor 27 is connected to the constant voltage source 100, and the base of the transistor 26 is connected to the frequency discriminating circuit 21. NPN transistors 3 and 4 and NPN transistors 24 and 25 are both the first and second
The common emitters of the NPN transistors 3 and 4 are connected to the collector of the NPN transistor 26, and the common emitters of the NPN transistors 24 and 25 are connected to the collector of the NPN transistor 27. NPN transistors 3, 4 and NP
The collectors of N transistors 24 and 25 are PNP transistors 1 and 2 and PNP transistor 2 as in the conventional circuit shown in FIG.
2,23 active load is connected. Transistor 3
A first time constant circuit consisting of a resistor 8 and capacitors 14 and 15 is formed in the collector of the first horizontal AFC from this connection point.
An output signal is obtained, while the collector of the transistor 25 is similarly provided with a second time constant circuit composed of the resistor 32 and the capacitors 34 and 35, and a second horizontal AFC output signal is obtained from this connection point. The first and second horizontal AFC output signals are two NPN transistors 28 and 29 with their collectors and emitters connected in common.
Horizontal AFC taken out by the emitter follower circuit by
It is output to the output terminal 18. The resistor 33 is a load resistor of the emitter follower circuit.

In the horizontal AFC circuit of the present invention having the above circuit configuration, the NPN
The comparison circuit composed of the transistors 26 and 27 uses the output voltage of the constant voltage source 100 as a reference voltage, and the reference voltage and frequency discrimination circuit 21
Based on the result of comparison with the output voltage of, the NPN transistor 26 or 27 is turned on depending on whether the horizontal frequency is low or high. As a result, one of the first and second differential amplifiers described above operates and the other does not operate depending on the horizontal frequency, and the one horizontal AFC signal that is operating passes through the emitter follower circuit to the horizontal AFC output terminal 18 Will be output. Since the output of the differential amplifier that is not operating has a high resistance, the corresponding emitter follower circuit is turned off.

The frequency discrimination circuit described above can be easily realized by a known frequency-voltage conversion circuit. It goes without saying that the first and second time constant circuits are set to optimum time constants in the horizontal frequency region in which the first and second differential amplifiers operate.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention. In FIG. 2, the comparison circuit shown in FIG.
26, 27, 40, the horizontal frequency can be detected in three regions of low, middle and high by the output of the frequency discriminating circuit 21, and the first differential amplifier by the NPN transistors 3 and 4, NPN.
One of the second differential amplifier composed of the transistors 24 and 25 and the third differential amplifier composed of the NPN transistors 38 and 39 are operated in accordance with the horizontal frequency. First,
First, second, and third horizontal obtained from the second and third differential amplifiers
The AFC signal is output from the horizontal AFC output terminal 18 via an emitter follower circuit composed of NPN transistors 28, 29 and 41 which are also configured by commonly connecting the collector and the emitter. The time constant circuit of the first differential amplifier is a resistor 8 and a capacitor 14,1
The time constant circuit of the second differential amplifier is a resistor 32
And the capacitors 34 and 35. The time constant circuit of the third differential amplifier is composed of the resistor 44 and the capacitors 51 and 52. The time constant of each time constant circuit is set according to the horizontal frequency at which it operates.

〔The invention's effect〕

As described above, in the horizontal AFC circuit according to the present invention, a plurality of time constant circuits can be switched depending on the horizontal frequency, and optimal horizontal AFC operation can be obtained even when the horizontal frequency is switched.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the present invention, FIG. 3 is a waveform diagram explaining AFC operation, and FIG. It is a circuit diagram showing an example of a conventional horizontal AFC circuit. 1 to 7, 22 to 29, 36 to 41, 53 are transistors, 8 to 13, 30 to 3
3,42 to 48 are resistors, 14,15,34,35,51,52 are capacitors, 16,
17, 54, 100 are constant voltage sources, 18 is a horizontal AFC output terminal, and 21 is a frequency discrimination circuit.

Claims (1)

[Claims] 1. A flyback pulse is applied to the base of a differential amplifier in which the emitters of two transistors are commonly connected, and a horizontal synchronizing signal is applied to the bases of switching transistors in cascade connection to the common emitter. Horizontal AF with active load and time constant circuit connected to output end
In the C circuit, a plurality of combinations of the differential amplifier, the active load, and the time constant circuit are provided, and the frequency of the horizontal synchronizing signal is set to a voltage between the common emitter of each of the plurality of differential amplifiers and the switching transistor. A comparator circuit is provided which is controlled by the output of the frequency discriminating circuit for conversion and connects one of the plurality of differential amplifiers to the switching transistor according to the frequency of the horizontal synchronizing signal, and outputs the outputs of the plurality of differential amplifiers respectively. The horizontal AFC circuit is characterized in that the horizontal AFC output is taken out from the common emitter of the emitter follower in which the collector and the emitter are commonly connected to the base.