Video processing circuit with IF AGC loop, auxiliary video clamp and shared reference voltage source formed on common integrated circuit

DETAILED DESCRIPTION The receiver 10 of FIG.
1 includes an antenna input terminal 12 for receiving an RF modulated video input signal and an auxiliary input terminal 14 for receiving a baseband composite video input signal provided by an external source.
Terminal 12 is applied to a tuner 16 having an output applied to a mixer 18 which provides an IF frequency signal to an IF filter 20.
The IF output signal S1 is applied to the input 32 of an auxiliary video clamp 30 unit (outlined in phantom) which has a second input 34 coupled by a clamp capacitor 36 to input 14 for receiving the auxiliary video input signal.
Unit 30 also includes a switch having an output 38 providing a tuner detected composite video signal or the auxiliary clamped video signal.
The selected video signal from terminal 38 is applied to a picture processing unit 80 that provides a processed video signal to a display unit 82 (e.
g.
, a kinescope) for display.
A receiver control unit 86 (e.
g.
, a control microprocessor) supplies a tuning signal to tuner 16 for channel selection and supplies a tuner/auxiliary selection signal to input 40 of unit 30 to control a video switch 42 that selects tuner or auxiliary video.
Control unit also sends various control signals to processor 80 for controlling picture parameters such as hue, saturation, brightness and contrast.
The auxiliary clamp circuit 30 (outlined in phantom) is constructed in an integrated circuit and provides the functions of IF AGC control, tuner video detection and auxiliary video clamping and video signal selection.
The IF AGC loop 43 includes an IF amplifier which amplifies the signal at terminal 32 and applies it to a video detector 46 that provides a composite video signal to a sound trap and to one input of the AGC comparator 48.
This comparator has a current source output connected to pin 52, to which the AGC capacitor 50 is attached (off chip); and connected to the gain control input of the IF amplifier.
The reference voltage V2 for the AGC comparator is provided by a bias generator 60