6

Typical Application

The EL4089 can be used to DC-restore a video waveform

(see Figure 1). The circuit forces the cable driving video

amplifier’s output to ground when the HOLD pin is at a logic

low.

The “correction voltage” is stored on capacitor CX1, an

external ceramic capacitor. The capacitor value is chosen

from the system requirements. The typical input bias current

to the video amplifier is 1µA, so for a 62µs hold time, and a

0.01µF capacitor, the output voltage drift is 6.2mV in one

line.

The S/H amplifier can provide a typical current of 300µA to

charge capacitor CX1, so with a 1.2µs sampling time, the

output can be corrected by 36mV in each line.

Using a smaller value of CX1 increases both the voltage that

can be corrected, and the drift while being held, likewise,

using a larger value of CX1, reduces the voltages.

The RX1 resistor is in the circuit purely to simulate some

external source impedance, and is not needed as a real

Frequency Response Flatness

Differential Gain vs DC Input

Differential Phase vs DC Input

8-Pin Plastic DIP

Maximum Power Dissipation

vs Ambient Temperature

8-Lead SO

Maximum Power Dissipation

vs Ambient Temperature

EL4089