Electronic Design

Simplify Sync Stretch Circuit

<p>During processing, a video sync signal will occasionally become compressed. This circuit, essentially made up of Q1, Q2, and Q3, comprises a video amplifier and sync stretch circuit (<a href="/Files/29/11457/Figure_01.gif">see the figure</a>). Q4 is an emitter follower that interfaces with following circuits.</p> <p> Q1 sync strips the incoming video at a level determined by R<sub>9</sub>. The incoming video is amplified and mixed with the stripped sync in Q2. Q3 provides inversion and video amplitude control via R<sub>15</sub>.</p> <p> It may be appropriate in some circuits to provide a degree of high-frequency equalization through a small-value capacitor (C<sub>eq</sub>), as shown in the figure, depending upon circuit layout.</p> <p> In the setup, the sync level control (R<sub>9</sub>) and the video level control (R<sub>15</sub>) are used to set the ratio of sync to the video desired. They also set the output video at 1 V p-p. </p>

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