| 摘要 |
In a signal measurement or processing system, specifically in a system which contemplates measurement or processing of video information and which is particularly adapted for use with microprocessors or microcomputers characterized by modest memory capacity and computational capability, a digital hysteresis circuit that enhances the quantization of an analog video signal. The hysteresis circuit is part of a transition detector that quantizes the brightness component of a composite video signal level into mutually exclusive and exhaustive BLACK and WHITE levels determined with regard to a THRESHOLD level. The THRESHOLD is established by applying a REFERENCE voltage, derived from the peak amplitude of the video signal, to a reference input of a D/A. The THRESHOLD is then established as a predetermined percentage of the REFERENCE voltage, as determined by a multibit digital CONTROL signal applied to the CONTROL input of the D/A. Digital hysteresis is effected by adding or subtracting appropriate digital bits from the primary digital control signal subsequent to WHITE-TO-BLACK and BLACK-TO-WHITE transistions, respectively, in the video signal. In a specific embodiment the circuit includes a digital substractor and adder to form the desired resultant digital control signals and a multiplexer to couple the resultant to the CONTROL input of the D/A.
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