SECAM modulator

Details SECAM modulator SECAM modulator

1977-11-15

1979-03-20

Richardson, Robert L.

Facsimile and static presentation processing

Static presentation processing

Attribute control

H04N 934, H04N 940, H04N 942

Patent

active

041457110

ABSTRACT:
Apparatus for forming a color TV signal of a SECAM type from a pair of correlated color-difference signals (R-Y; B-Y) includes a pair of transistors disposed in a differential amplifier configuration, with a constant current source coupled to interconnected emitters, and a load impedance coupled to one collector. Pre-emphasized B-Y signal is applied to first transistor base during alternate line scanning intervals; pre-emphasized R-Y signal is applied to second transistor base during intervening line scanning intervals. Electronic switches control bias application to transistor bases so that (a) during horizontal sync intervals bases are equally biased; (b) during alternate line scanning intervals (and preceding "backporch" intervals) base bias of second transistor is elevated relative to the first; and (c) during intervening line scanning intervals (and preceding "backporch" intervals) base bias of first transistor is elevated relative to the second. During alternate line interval segments of terminal portion of vertical blanking interval, base bias of first transistor is initially held at abovementioned elevated level relative to the second and then allowed to gradually rise still higher; during the intervening line interval segments, similar control of base bias of second transistor is effected. VCO responds to changes in voltage drop across load impedance by varying its output frequency. In several illustrative applications, a synchronizing system using single reference is effective, during initial portion of horizontal sync interval, in adjusting VCO output to reference frequency. During terminal portion of horizontal sync interval, VCO output is shifted to a frequency midway between the two SECAM resting frequencies. In PAL-SECAM transcoder use, reference frequency is PAL subcarrier frequency; in video disc player use, reference frequency is subcarrier frequency of transcoded composite signal of NTSC-like form.

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