AD5539

REV. B

–16–

quency applications including color key switching. It features

both inverting and noninverting inputs and can provide an out-

put of

±1 V into a reverse-terminated 75 Ω load (or ±2 V into

150

Ω). An optional output offset adjustment is provided. The

input range of the video switch is the same as the output range:

±1 V at either input generates ±1 V (noninverting) or 1 V

(inverting) across the 75

Ω load. The circuit provides a gain of

about 1, when “ON,” or zero when “OFF.”

The differential configuration uses both channels of the AD539

not only to provide alternative input phases, but also to elimi-

nate the switching pedestal due to step changes in the output

current as the AD539 is gated on or off.

Figure 49 shows the response to a pulse of 0 to +1 V on the

signal channel. With the control input held at zero, the rise

time is under 10 ns. The response from the inverting input

is similar.

The differential-gain and differential-phase characteristics of

this switch are compatible with video applications. The incre-

mental gain changes less than 0.05 dB over a signal window of 0

to +1 V, with a phase variation of less than 0.5 degree at the

subcarrier frequency of 3.58 MHz. The noise level of this cir-

cuit measured at the 75

Ω load is typically 200 µV in a 0 MHz

to 5 MHz bandwidth or approximately 100 nV per root hertz.

The noise spectral density is essentially flat to 40 MHz.

The waveforms shown in Figures 48 and 49 were taken across a

75

Ω termination; in both photos, the signal of 0 to +1 V (in

this case, an offset sine wave at 1 MHz) was applied to the

noninverting input. In Figure 48, the envelope response shows

the output being fully switched in about 50 ns. Note that the

output is ON when the control input is zero (or more negative)

and OFF for a control input of +1 V or more. There is very

little control-signal breakthrough.

Figure 48. The Control Response of the Video Switcher

Figure 49. The Signal Response of the Video Switcher

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

14-Pin Cerdip Package

(Q-14)

14-Pin Plastic DIP Package

(N-14)