Wideband analog RGB video processor with negative feedback capability and black level control

A method for providing wideband analog RGB processing comprising:

• converting receiver R, G and B component video voltage signals into R, G and B component video current signals;
• amplifying said R, G and B component video current signals to provide a desired gain;
• converting said amplified R, G and B component video current signals into R, G and B component video voltage signals;
• amplifying said R, G and B component video voltage signals to generate R, G and B output signals for driving video display means;
• providing a feedback signal from a low voltage signal representative of said R, G and B component video voltage signals soleley during scan retrace intervals during which video is not present;
• comparing said feedback signal with a reference signal to generate a variable DC correction current;
• combining said correction current with said R, G and B component video current signals before said conversion of said R, G and B component current video signals into R, G and B video voltage signals.

A wideband analog RGB video processor comprising:

• gain control means including, voltage-to-current conversion means for converting received individual R, G and B voltage signals into individual R, G and B current signals and amplifying means coupled to said conversion means for providing desired gain for individual R, G and B current signals;
• combining means for combining said individual R, G and B current signals with individual correction current signals, said combining means including current-to-voltage conversion means for converting said combined individual R, G and B current signals to produce voltage signals;
• video output means coupled to said combining means for producing individual R, G and B output signals to drive desired color video display means and having at least one node at which a relatively low voltage level signal representative of said R, G and B output signals typically is present;
• and
• feedback means coupled to said low voltage node to provide a feedback signal for coordinating said output voltage signals with said individual R, G and B current signals, said feedback means including voltage-to-current conversion means for providing individual R, G and B correction current signals and signal reference means, whereby the individual R, G and B current correction signals may be controlled by adjusting said signal reference, said feedback means is controlled by periodic gating signals corresponding to a scan retrace interval during which video is not present.

A video processing system having a video output stage, including output driver means having at least one node at which a relatively low voltage level signal representative of the output voltage signal is typically present, and combining means for combining component video current signals with correction current signals for wideband RGB processing and having a feedback control means for providing optimum correction current signals comprising:

• voltage reference signal mans for providing a voltage reference signal;
• comparator means coupled to said low level node in said output stage and to said voltage reference means for comparing said representative output voltage signal at said low level voltage with said voltage reference signal to produce differential voltage signal representative of the difference between the compared signals;
• voltage-to-current conversion means for providing a correction current signal to said combining means, the magnitude and polarity of said correction current signal being representative of said differential voltage signal;
• said comparator means being adapted to receive periodic gating signals corresponding to scan retrace intervals during which no video is present to control said comparator means, whereby said low level, representative output voltage signal is compared to said voltage reference signal by said comparator means only during said scan retrace interval.

In a wideband RGB video processing system utilizing video components current signals for signal processing and video component voltage signals for output and having a video output stage, an improved feedback control circuit for providing correction current signals comprising:

• variable voltage reference signal means for providing variable, determinable voltage reference signals;
• gated comparator means coupled to said output stage to receive low voltage output signals and coupled to said voltage reference signal means for receiving said variable voltage reference signals and adapted to receive a gating pulse signal corresponding to the scan retrace interval during which no video is present in the video signal to compare said low voltage representative video component output signals to said variable voltage reference signals only during said scan retrace interval to produce a correction voltage signal representative of the difference between the compared signals;
• voltage to current conversion means coupled to recieve said differential voltage signal for providing a correction current signal, the magnitude and polarity of said correction current signal being representative of said differential voltage signal;
• and
• combining means for combining said correction current signal with said video component current signals.