AD5539
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. T he
input range of the video switch is the same as the output range:
±1 V at either input generates ±1 V (noninverting) or ϯ1 V
(inverting) across the 75 Ω load. T he circuit provides a gain of
about 1, when “ON,” or zero when “OFF.”
T he differential-gain and differential-phase characteristics of
this switch are compatible with video applications. T he 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. T he 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.
T he noise spectral density is essentially flat to 40 MHz.
T he 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.
T he 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. T here is very
little control-signal breakthrough.
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. T he response from the inverting input
is similar.
Figure 49. The Signal Response of the Video Switcher
Figure 48. The Control Response of the Video Switcher
O UTLINE D IMENSIO NS
D imensions shown in inches and (mm).
14-P in Cer dip P ackage
(Q -14)
14-P in P lastic D IP P ackage
(N-14)
–16–
REV. B