LMC7101_15 Datasheet, PDF (23/33 Pages) Texas Instruments – LMC7101, LMC7101Q-Q1 Tiny Low-Power Operational Amplifier With Rail-to-Rail Input and Output

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Application Information (continued)
LMC7101, LMC7101Q-Q1
SNOS719G – SEPTEMBER 1999 – REVISED SEPTEMBER 2015
Figure 65. Cancelling the Effect of Input Capacitance
8.2 Typical Application
Figure 66 shows a high input impedance noninverting circuit. This circuit gives a closed-loop gain equal to the
ratio of the sum of R1 and R2 to R1 and a closed-loop 3-dB bandwidth equal to the amplifier unity-gain
frequency divided by the closed-loop gain. This design has the benefit of a very high input impedance, which is
equal to the differential input impedance multiplied by loop gain. (Open loop gain/Closed loop gain.) In DC
coupled applications, input impedance is not as important as input current and its voltage drop across the source
resistance. The amplifier output will go into saturation if the input is allowed to float, which may be important if
the amplifier must be switched from source to source.
R₂
R₁
IN
V+
–
+
OUT
V–
Figure 66. Example Application
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