4
FN7049.1
February 11, 2005
Applications Information
Gain Equation
V
OUT
= ((R2+R1)/R1) x (V
IN
-V
INB
+V
REF
) when R1 tied to
GND
V
OUT
= ((R2+R1)/R1) x (V
IN
-V
INB
) when R1 tied to V
REF
Choice of Feedback Resistor
For a gain of one, V
OUT
may be shorted back to V
FB
, but
100Ω-200Ω improves the bandwidth. For gains greater than
one, there is little to be gained from choosing resistor R1
value below 200Ω, for it would only result in increased power
dissipation and potential signal distortion. Above 200Ω, the
bandwidth response will develop some peaking (for a gain of
one), but substantially higher R1 values may be used for
higher voltage gains, such as up to 1kΩ at a gain of four
before peaking will develop.
Capacitance Considerations
As with many high bandwidth amplifiers, the EL2142 prefers
not to drive highly capacitive loads. It is best if the
capacitance on V
OUT
is kept below 10pF if the user does not
want gain peaking to develop. The V
FB
node forms a
potential pole in the feedback loop, so capacitance should
be minimized on this node for maximum bandwidth.
The amount of capacitance tolerated on any of these nodes
in an actual application will also be dependent on the gain
setting and the resistor values in the feedback network.
Typical Applications Circuits
FIGURE 1. TYPICAL TWISTED PAIR APPLICATION
50Ω
V
FB
50Ω
EL2142
V
IN
V
INB
V
REF
V
OUT
100Ω
FIGURE 2. COAXIAL CABLE DRIVER PAIR APPLICATION
EL2142
