JPS616983A - Dc reproducing circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a DC regeneration circuit which has a wide output operating range and is suitable for semiconductor integrated circuits.

Configuration of a conventional example and its problems An example of a conventional DC regeneration circuit is shown in FIG. In Fig. 1, 1 is a PNP l-transistor for a buffer to pass the DC-regenerated signal to the next stage, 2 is a transistor of the same type with its emitter connected to the collector of transistor 1, and 3
and 4, a transistor for inverting the base current of transistor 2; 6, a current source that supplies current to transistor 1; 6, a capacitor for DC reproduction; 7, a video signal source; 8, for DC reproduction. 9 is a constant voltage source, and 10 is a power supply terminal.

In the operation of this circuit, during the retrace period of the video signal, the switch 8
is made conductive, the DC voltage during the retrace period is made to match the constant voltage source 9 at the base terminal of the transistor 1, and the switch 8 is opened during the video period of the video signal to keep the potential difference between both ends of the capacitor 6 constant. The base current of the transistor 1 is adjusted so that the DC power does not flow to the capacitor 6.
This is to compensate for the polarity of the base current of transistor 2 and the current reversed by transistor 3 and transistor 4. However, the output operating range at the emitter of buffer transistor 1 and the emitter voltage of transistor 2 It cannot be lower than. This causes a problem when the voltage is low and the signal has an amplitude above and below the voltage during the retrace period.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a DC regeneration circuit that overcomes the drawbacks of the conventional DC regeneration circuit, that is, expands the narrow output operating range of the conventional DC regeneration circuit.

Structure of the Invention In the present invention, it is possible to add the base current of a buffer transistor to the base current of another transistor having the same shape as the buffer transistor and having the same emitter current by reversing the polarity using a current mirror circuit. This is a DC regeneration circuit that compensates for the DC current so that it does not flow f''L into the DC regeneration capacitor during the video period, and expands the output operation range of the DC regenerated signal.

DESCRIPTION OF THE EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG.

In this DC regeneration circuit, the base of the DC regeneration buffer transistor 1 connected to the first current source 5 and the base of a transistor 20 which is connected to the second current source 12 and whose emitter current is equal to that of the buffer transistor 1 are connected. are connected by a current mirror circuit so that the base currents are equal to each other, and the structure is such that no DC current flows to the DC reproduction capacitor during the video period. The capacitor 6 for DC reproduction, the video signal source 7, the switch 8, and the constant voltage source 9 are the same as those shown in FIG.

With this configuration, it is possible to lower the emitter voltage of transistor 1 to the ground potential.
As shown in FIG. 3, it is also possible to use it as part of a differential amplifier consisting of a transistor 1 connected to a current source 6 and a transistor 14 connected to a current source 13. Note that the resistance is 15°16.

In Figure 2, P as the DC regenerative Vanofa transistor 1
I used an NP type transistor, but when using an NPN type,
With the configuration shown in FIG. 4, it is possible to increase the emitter voltage of transistor 1 using the power supply potential trench. The numbers in the figure in FIG. 4 correspond to the numbers in the figure in FIG. 2, and they play the same role.

Effects of the Invention When a PNP type is used for the emitter potential of the DC regeneration buffer transistor of the present invention (1.
When a type is used, it is possible to obtain an amplitude up to the power supply voltage, and the limitation on the amplitude of the emitter of transistor 1 due to transistors 2 and 3, which was shown in the conventional example, is eliminated.

Further, as shown in FIG. 3, it is also possible to use the DC regeneration buffer transistor 1 for other functions, which greatly increases the scope of application of the present invention.

[Brief explanation of drawings]

FIG. 1 is a DC regeneration circuit diagram of a conventional example, and FIGS. 2, 3, and 4 are circuit diagrams of an embodiment of the present invention. 1.2,3,4.14...Transistor, 5°12
．． 13 Constant current source, 9... Constant voltage source, 10-Power supply, 6 - Capacitor, A... Signal source, 8 Switch, H, 1
1 Output terminal, 15, 16...Resistor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure

Claims (1)

[Claims] The emitter of the first transistor is connected to the first current supply source, the emitter of the second transistor is connected to the second current supply source, and the base currents of the two transistors are supplied through a current mirror circuit. A DC regeneration circuit that combines DC regeneration means with the base.