LM7171

SNOS760B – MAY 1999 – REVISED MARCH 2013

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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 510

Ω 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

(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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