JPS6250017B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a blanking circuit for a television receiver, and in particular, a flyback pulse is applied to an external terminal provided on a circuit block such as an integrated circuit via an external resistor. and the same circuit capable of deriving a vertical blanking signal.

Integrated circuits (hereinafter referred to as integrated circuits) used in conventional television receivers
In order to process various signals, ICs are equipped with input terminals to apply input signals and output terminals to derive output signals as external terminals (also called terminal pins or simply pins). The problem of reducing the number of pins in the blanking circuit that derives the ranking signal has not yet been solved.

The present invention has been made in view of the above drawbacks, and will be explained below with reference to the drawings. FIG. 1 shows the blanking circuit of the present invention, FIG. 2 A to D show waveforms of each part of FIG . A comparator consisting of transistors 2 and 3, 4 a first voltage dividing resistor network consisting of resistors 5 and 6, 7 an emitter resistor, 8 a load resistor, 9
is an emitter follower stage, 10 is a second voltage dividing resistor network consisting of resistors 11 and 12, 13 is a blanking transistor, 14 is a clip diode, 15 is an external terminal, 16 is an external resistor, and 17 is a flyback pulse application. Terminal, 18 is power supply terminal, 1
9 is a blanking pulse application terminal, 20 is an output terminal from which a horizontal blanking signal is obtained, and the area within the dashed line indicates the IC internal circuit.

Next, to explain the operation of the circuit of the present invention, the terminal 17 receives a flyback pulse V as shown in FIG.
_D is added, and a vertical blanking pulse V _B shown in FIG. 2B is applied to the base of the blanking transistor 13.

At this time, the external terminal 15 is connected to the clip diode 14 as shown in FIG.
A waveform clipped at (VCC+Vf) (Vf is the forward voltage of the clipping diode) appears. On the other hand, since the above-mentioned vertical blanking signal is applied to the terminal 19, the blanking transistor 13 is turned off during the vertical blanking period, and the base voltage of the emitter follower stage 9 is VCCR ₆ /(R ₅ +
_R6 ).

Here, when the values R ₅ and R ₆ of the resistors 11 and 12 are equal (R ₅ =R ₆ ), the base voltage of the emitter follower stage 9 becomes VCC/2.

When the clip waveform of the flyback pulse V _D and the vertical blanking pulse are superimposed,
As a whole, _the waveform V _C shown in FIG. Blanking can be performed.

Further, a voltage V _A that can be used as a horizontal blanking signal appears at the output terminal 20 of the comparator 1 , making it possible to perform horizontal blanking within the IC shown by the dashed line.

_The voltage V 1 at one input terminal of the comparator, which is the voltage dividing point of the first voltage dividing resistor network 4, is set higher than (voltage dividing point voltage −V _BE ) of the second voltage dividing resistor network 10 . and the voltage at the other input terminal of comparator 1
V ₂ becomes higher than V ₁ only during the flyback period, and when the base of transistor 3 becomes higher than the base of transistor 2, transistor 2 turns on, current flows through load resistor 8, and voltage V at terminal 20 as described above. _A will appear.

As described above, according to the present invention, a horizontal blanking signal is generated at a terminal within the circuit block by a vertical blanking signal generated within the same circuit block such as an IC and a flyback pulse applied from the outside. Horizontal and vertical blanking signals can be derived from the external terminal to which the flyback pulse is applied, and one external terminal can take in an external signal and output the internal signal to the outside. .

The same effect can be obtained by using a clip transistor instead of the clip diode mentioned above, and if the external resistor is used to compensate for the small internal impedance of the flyback transformer source, the optimal value can be selected. good.

[Brief explanation of the drawing]

FIG. 1 shows a blanking circuit of the present invention, and FIGS. 2A to 2D show waveforms of various parts in FIG. Explanation of main figure numbers, 1 ...Comparator, 4 ...First voltage dividing resistor network, 9...Emitter follower stage, 1
0...Second voltage dividing resistor network, 14...Clip diode, 15...External terminal, 16...External resistor.

Claims (1)

[Claims] 1 Comparison means having a pair of input terminals, a first voltage dividing resistor network to which one of the input terminals is connected and divides the power supply voltage, and an external terminal and an emitter follower stage to which the other input terminal is connected. , a blanking transistor to which the input terminal of the emitter follower stage is connected and whose collector-emitter path is connected in parallel to a part of a second voltage dividing resistor network that divides the power supply voltage; and the external terminal and the power supply terminal. a circuit block such as an integrated circuit having a clip means connected between the circuit block and an external resistor connected between the external terminal of the circuit block and a flyback application terminal; At the same time as applying a back pulse, a vertical blanking pulse is applied to the input terminal of the blanking transistor, a horizontal blanking signal is derived from the output side of the comparing means, and horizontal and vertical blanking pulses are derived from the external terminal. A blanking circuit characterized by: