| 摘要 |
<p>In a SECAM-PAL transcoder, color-difference signals, sequentially recovered from received SECAM signals by a single FM discriminator (15), are supplied via a first emitter-follower (30) to a first modulating signal input terminal (M) of a balanced modulator (35), which develops a quasi-PAL signal output using PAL subcarrier frequency oscillations applied in push-pull at carrier terminals (C, C) thereof. A DC potential, supplied to a second modulating signal input terminal (M min ) of the modulator via a second emitter-follower (70), matches discriminator output level under no-color signal conditions. Third and fourth emitter-followers (90, 100), responsive to a blanking waveform (BL), effects cutoff of the first and second emitter-followers (30, 70) during blanking periods and delivers an elevated planking pedestal to the first terminal (M) and a matching blanking pedestal to the second terminal (M min ). During a portion of the blanking period, a burst gating pulse (BG) supplied via the third emitter-follower (90) causes departure from the blanking pedestal level at the first terminal (M) without disturbing the blanking pedestal level at the second terminal (M min ) to develop a burst component of controlled magnitude in the quasi-PAL signal output from the modulator (35).</p> |
