The AD9280ARS features an optional clamp circuit for dc restoration of video or ac coupled signals. Figure 24 shows the internal clamp circuitry and the external control signals needed for clamp operation. To enable the clamp, apply a logic high to the CLAMP pin. This will close the switch SW1. The clamp amplifier will then servo the voltage at the AIN pin to be equal to the clamp voltage applied at the CLAMPIN pin. After the desired clamp level is attained, SW1 is opened by taking CLAMP back to a logic low. Ignoring the droop caused by the input bias current, the input capacitor CIN will hold the dc voltage at AIN constant until the next clamp interval. The input resistor RIN has a minimum recommended value of 10 W, to maintain the closed-loop stability of the clamp amplifier.