Dc restoration and white clipping circuit for video recorder

Claim 2

A DC restoration and clipping circuit for a composite video signal having sync tip peaks in one direction of signal swing and ''''white'''' peaks in the other direction of signal swing, comprising a two stage direct coupled transistor amplifier including a first stage to which the composite input signal is AC coupled, and second stage arranged such that when the DC input level to the first stage exceeds a predetermined level during ''''white'''' peak swings of the input, the second stage is cut off, means coupled to the output of the second stage for detecting peaks in the output corresponding to sync tip peaks in the input signal, and means coupled to the peak detecting means for adjusting the DC level at the input to the first stage in response to changes in the average level of the detected sync tip peaks at the output, whereby the sync tip level at the output remains fixed.

Claim 3

Apparatus as defined in claim 1 wherein the peak detecting means includes a transistor having a first electrode coupled to the output of the amplifier, a second electrode coupled to a fixed reference potential, and a third electrode connected to a potential source through a relatively large load resistance and connected to said fixed reference potential through a large capacitor, the load resistor and capacitor having an R-C time constant that is long compared to the period between sync tips of the composite video signal, the input to the first stage being connected to said third electrode to control the DC level at the input to the direct coupled amplifier.

Claim 4

Apparatus as defined in claim 1 wherein the direct coupled amplifier includes first and second transistors, means for AC coupling the input to the base of the first transistor, means connecting the collector of the first transistor to one side of a potential source, means connecting the collector of the second transistor to said one side of said source, and the base of the second transistor being connected to an intermediate fixed reference potential, separate emitter resistors connecting the emitters of both transistors to the other end of said source, and means for maintaining the combined current from said potential source through the two transistors substantially constant.

Claim 5

Apparatus as defined in claim 2 wherein the direct coupled amplifier includes first and second transistors, means for AC coupling the input to the base of the first transistor, means connecting the collector of the first transistor to one side of a potential source, means connecting the collector of the second transistor to said one side of said source, and the base of the second transistor being connected to an intermediate fixed reference potential, separate emitter resistors connecting the emitters of both transistors to the other end of said source, and means for maintaining the combined current from said potential source through the two transistors substantially constant.

Claim 6

Apparatus as defined in claim 3 wherein the means connecting the collector of the second transistor to the source includes a load resistor, the load resistor being connected as part of a voltage divider connected across said potential source, the output of the amplifier being derived from a tap on the voltage divider, the portion of the voltage divider between the collector end of the load resistor and the output tap including a variable resistor for adjusting the peak-to-peak swing of the output.

Claim 7

A circuit for restoring a DC level to the peaks of one polarity of an AC signal and clipping the peaks of the opposite polarity, comprising a direct coupled amplifier, the amplifier having a transfer characteristic that is linear over a range of input levels and that levels off abruptly at one end of the linear range, means for detecting the signal peaks of said one polarity at the output of the amplifier, said detecting means including means for comparing the detected peaks with a reference potential, means responsive to the detecting means for controlling the DC level at the input of the amplifier to maintain the level of said detected peaks constant in relation to said reference potential, and means for adjusting the DC level at the input to a level within said linear range such that peaks of the input signal of said opposite polarity swing the input out of the linear range when said opposite polarity peaks of the input signal exceed a predetermined amplitude.

Claim 8

A circuit for restoring a DC level to the peaks of one polarity of an AC signal and clipping the peaks of the opposite polarity, comprising a direct coupled amplifier, the amplifier having a transfer characteristic that is linear over a range of input levels and that levels off abruptly at one end of the linear range, means for detecting the signal peaks of said one polarity at the output of the amplifier, said detecting means including means for comparing the detected peaks with a reference potential, means responsive to the detecting means for controlling the DC level at the input of the amplifier to maintain the level of said detected peaks constant in relation to said reference potential, and means for adjusting the DC level at the input to a level within said linear range such that peaks of the input signal of said opposite polarity swing the input out of the linear range when said opposite polarity peaks of the input signal exceed a predetermined amplitude.

Claim 9

Apparatus as defined in claim 6 wherein said direct coupled amplifier includes first and second transistors, a constant current source, means for connecting the collectors of said transistors to one terminal of said source, means including separate resistors in series with the respective emitters of the two transistors connecting the emitters to the other terminal of said source, means for holding the base of one transistor at a constant reference potential, the input signal being coupled to the base of the other transIstor.

Claim 10

Apparatus as defined in claim 6 wherein the peak detecting means includes a transistor having a first electrode coupled to the output of the amplifier, a second electrode coupled to a fixed reference potential, a third electrode connected to a potential source through a relatively large load resistance and connected to said fixed reference potential through a large capacitor, the load resistor and capacitor having an R-C time constant that is long compared to the period between peaks of said one polarity, and resistor means connecting said third electrode to the input to the amplifier to control the DC level at the input to the amplifier.

Claim 11

Apparatus as defined in claim 7 wherein the peak detecting means includes a transistor having a first electrode coupled to the output of the amplifier, a second electrode coupled to a fixed reference potential, a third electrode connected to a potential source through a relatively large load resistance and connected to said fixed reference potential through a large capacitor, the load resistor and capacitor having an R-C time constant that is long compared to the period between peaks of said one polarity, and resistor means connecting said third electrode to the input to the amplifier to control the DC level at the input to the amplifier.