Blanking and black level control circuit for video signals

Claim 2

A blanking an black level insertion circuit for a video signal of the type having periodic scan and blanking periods, comprising a source of said signal, an output circuit, direct current amplifier means, commutating means synchronized with said signal and having a first position during said scan periods for connecting said source of a signal to said output circuit and for interconnecting the input and output of said amplifier means to form a loop circuit, said commutating means having a second position during said blanking periods for interrupting said loop circuit and connecting said source to aid output circuit by way of said amplifier means, said blanking and black level circuit further comprising capacitor means connected between a point of reference potential and a first point on the loop circuit which is formed during said blanking periods, a source of black level control voltage, and means connecting said source of control voltage to a second point on said loop circuit which is between the output of said amplifier and said output circuit during said scan intervals.

Claim 3

A blanking and black level insertion circuit for a video signal of the type having periodic scan and blanking periods, comprising a source of said video signal, an output circuit, direct current amplifier circuit means, commutating means having first position connecting said source to said output circuit and interconnecting the input and output of said amplifier means to form a loop circuit, and a second position interrupting said loop circuit and connecting said source to said output circuit by way of said amplifier means, capacitor means, means connecting said capacitor means between said amplifier means and a point of reference potential whereby said capacitor means bypasses said video signal when said commutating means is in its first position, a source of black level current, means applying said black level current to the output of said amplifier means whereby said black level current circulates in said loop circuit when said commutating means is in its second position and is applied to said output circuit when said commutating means is in its first position, and control means connected to said commutating means and synchronized with said video signal whereby said commutating means is in said first position during said scan periods and is in said second position during said blanking periods.

Claim 4

A blanking and black level insertion circuit for a video signal of the type having periodic scan and blanking periods, comprising a source of said video signal, an output circuit, direct current amplifier circuit means, commutating means having first position connecting said source to said output circuit and interconnecting the input and output of said amplifier means to form a loop circuit, and a second position interrupting said loop circuit and connecting said source to said output circuit by way of said amplifier means, capacitor means, means connecting said capacitor means between said amplifier means and a point of reference potential whereby said capacitor means bypasses said video signal when said commutating means is in its first position, a source of black level current, means applying said black level current to the output of said amplifier means whereby said black level current circulates in said loop circuit when said commutating means is in its second position and is applied to said output circuit when said commutating means is in its first position, and control means connected to said commutating means and synchronized with said video signal whereby said commutating means is in said first position during said scan periods and is in said second position during said blanking periods.

Claim 5

The circuit of claim 2 wherein said commutating means comprises a first transistor having its emitter-collector path connected between aid source of a signal and said output circuit, a second transistor having its emitter-collector path connected between said source of a signal and the input of said amplifier means, a third transistor having its emitter-collector path connected between the output of said amplifier means and said output circuit, and a fourth transistor having its emitter-collector path connected between the output and input of said amplifier means.

Claim 6

The circuit of claim 3 wherein said control means comprises a source of blanking pulses, means applying said blanking pulses to the base of one of said transistors connected to said source of signals and to the base of one of said transistors connected to the output of said amplifier means, and means applying bias potentials to the bases of the remaining transistors whereby said first and fourth transistors are conductive during said scan periods and said source and third transistors are conductive during said blanking periods.

Claim 7

The circuit of claim 3 wherein said first, second, third and fourth transistors are of one conductivity type, said source of signal comprises a fifth transistor of he same conductivity type having its collector connected only to the emitter of aid first and second transistors, means applying said signal to the base of said fifth transistor, and means connecting the emitter of said fifth transistor to a point of constant potential, and said output circuit comprises a sixth transistor of opposite conductivity type connected as a common emitter amplifier with its base connected to the collectors of said first and third transistors.

Claim 8

The circuit of claim 2 wherein said amplifier means comprises an amplifier having an input terminal, an output terminal a first transistor of one conductivity type having its collector connected to said input terminal, a second transistor of the same conductivity type having its collector connected to aid output terminal, a third transistor of the same conductivity type having its base connected to aid input terminal and its emitter connected to the bases of said first and second transistors, means connecting the collector of said third transistor to a point of constant potential, and separate resistor means connecting the emitters of said first and second transistors to at least one point of constant potential.

Claim 9

The circuit of claim 6 wherein at least one of said resistor means comprises a voltage divider connected between two different points of constant potential and having a tap connected to the emitter of the respective transistor, said voltage divider being variable whereby the gain of said amplifier can be varied.

Claim 10

A circuit for blanking and black level insertion of a video signal of the type having scan periods and blanking periods, comprising a source of said signal, an output circuit, means connecting said source of said signal to said output circuit, a loop circuit including direct current amplifier means and means interconnecting the input and output of aid amplifier means, a source of black level current, means applying said black level current to said loop circuit between the input and output of said black means, capacitor means, means connecting said capacitor means between a point of said loop circuit an a point of reference potential, and commutating means connected to interrupt said loop circuit and connect said source of said signal to said output by way of said amplifier means during said blanking periods, whereby said capacitor bypasses said video signal and said black level current is applied to said output circuit directly during said blanking periods.

Claim 11

A circuit for blanking and black level insertion of a video signal of the type having scan periods and blanking periods, comprising a source of said signal, an output circuit, means connecting said source of said signal to said output circuit, a loop circuit including direct current amplifier means and means interconnecting the input and output of aid amplifier means, a source of black level current, means applying said black level current to said loop circuit between the input and output of said black means, capacitor means, means connecting said capacitor means between a point of said loop circuit an a point of reference potential, and commutating means connected to interrupt said loop circuit and connect said source of said signal to said output by way of said amplifier means during said blanking periods, whereby said capacitor bypasses said video signal and said black level current is applied to said output circuit directly during said blanking periods.