Facsimile and static presentation processing – Static presentation processing – Attribute control
Patent
1985-08-14
1987-06-23
Shepperd, John W.
Facsimile and static presentation processing
Static presentation processing
Attribute control
358 74, H04N 972
Patent
active
046757260
ABSTRACT:
Drive adjustment control for video output stage is provided through the use of a variable resistance network coupled with the video output stage. Variation in CRT phosphorous levels and attainment of desired white level signal gain ratios in the video output signals may be achieved through the use of the present invention. A variable resistive network is utilized to change the equivalent emitter resistance in a cascode output stage so that the white level, AC amplitude, of the video output signal may be effectively varied without affecting the black level component of the video output signal. Feedback circuitry selectively maintains a desired voltage across an emitter resistor during drive adjustment. A voltage divider network coupled to the feedback circuit maintain a second node at said desired voltage during drive adjustment. A variable resistor connected between the second node and the emitter resistor may then be varied during drive adjustment without changing the DC current drawn through the variable resistor and hence the current through the output stage. Accordingly, the DC component of the video signal is maintained at a desired value and the AC amplitude may be desirably varied by changing the setting of the variable resistor.
REFERENCES:
patent: 4203131 (1980-05-01), Harwood et al.
patent: 4331982 (1982-05-01), Parker
patent: 4414577 (1983-11-01), Tallant et al.
patent: 4547799 (1985-10-01), Rodgers
Shepperd John W.
Zenith Electronics Corporation
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