EL4421C/22C/41C/42C/43C/44C
Multiplexed-Input Video Amplifiers
Applications Information Ð Contd.
g
g
The logic input(s) and ground pin are shifted
2.5V above system ground to correctly bias the
mux-amp. Of course, all the signal inputs and
output will have to be shifted 2.5V above system
ground to ensure proper signal path biasing.
is again 3V and the output swing is 6V. The
EL4443 or EL4444 can be wired for inverting
gain with even more amplitude possible.
The output and positive inputs respond to over-
loading amplitudes correctly; that is, they simply
clamp and remain monotonic with increasing
A final caution: the ground pin is also connected
to the IC’s substrate and frequency compensation
components. The ground pin must be returned to
system ground by a short wire or nearby bypass
capacitor. In figure 2, the 22 KX resistors also
serve to isolate the bypassed ground pin from the
a
where the input of an active stage is overdriven
input overdrive. A condition exists, however,
b
by large outputs. This occurs mainly in unity-
gain connections, and only happens for negative
inputs. The overloaded input cannot control the
feedback loop correctly and the output can be-
come non-monotonic. A typical scenario has the
a
5V supply noise.
g
circuit running on 5V supplies, connected for
unity gain, and the input is the maximum 3V.
Negative input extremes can cause the output to
Signal Amplitudes
Signal input and output voltages must be be-
g
b a
a b
) 2.5V to ensure
linearity. Additionally, the differential voltage on
tween (V
)
2.5V and (V
b
b
jump from 3V to around 2.3V. This will nev-
er happen if the input is restricted to
g
2.5V,
g
any input stage must be limited to 6V to pre-
vent damage. In unity-gain connections, any in-
which is the guaranteed maximum input compli-
g
ance with 5V supplies, and is not a problem
g
put could have
3V applied and the output
with greater supply voltages. Connecting the
feedback network with a divider will prevent the
overloaded output voltage from being large
g
would be at 3V, putting us at our 6V differen-
tial limit. Higher-gain circuit applications divide
the output voltage and allow for larger outputs.
b
enough to overload the input and monotonic
a
For instance, at a gain of 2 the maximum input
11
ELANTEC [ ELANTEC SEMICONDUCTOR ]
