Datasheet

LM7171
SNOS760B –MAY 1999–REVISED MARCH 2013 www.ti.com
Component Selection and Feedback Resistor
It is important in high speed applications to keep all component leads short. For discrete components, choose
carbon composition-type resistors and mica-type capacitors. Surface mount components are preferred over
discrete components for minimum inductive effect.
Large values of feedback resistors can couple with parasitic capacitance and cause undesirable effects such as
ringing or oscillation in high speed amplifiers. For LM7171, a feedback resistor of 510Ω gives optimal
performance.
COMPENSATION FOR INPUT CAPACITANCE
The combination of an amplifier's input capacitance with the gain setting resistors adds a pole that can cause
peaking or oscillation. To solve this problem, a feedback capacitor with a value
C
F
> (R
G
× C
IN
)/R
F
(1)
can be used to cancel that pole. For LM7171, a feedback capacitor of 2 pF is recommended. Figure 57 illustrates
the compensation circuit.
Figure 57. Compensating for Input Capacitance
POWER SUPPLY BYPASSING
Bypassing the power supply is necessary to maintain low power supply impedance across frequency. Both
positive and negative power supplies should be bypassed individually by placing 0.01 μF ceramic capacitors
directly to power supply pins and 2.2 μF tantalum capacitors close to the power supply pins.
Figure 58. Power Supply Bypassing
TERMINATION
In high frequency applications, reflections occur if signals are not properly terminated. Figure 59 shows a
properly terminated signal while Figure 60 shows an improperly terminated signal.
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