LMV101 National Semiconductor Corporation, LMV101 Datasheet - Page 9

• Manufacturer Part Number: LMV101
• Description: Fixed-gain Amplifiers
• Manufacturer: National Semiconductor Corporation

Application Information
To improve power supply ripple rejection of the above micro-
phone preamplifier, another capacitor and a pot can be con-
nected to pin 1 as shown in Figure 6 . The impedance of the
two capacitors at audio frequencies are low. The R
be adjusted so that the supply ripples injected through both
the inverting input and the non-inverting input cancel each
other at the output. If we ignore the impedance of the capaci-
tors, we can select the pot value based on the following
equation:
Z
the gain of the preamplifier in absolute value.
OUT
FIGURE 5. Microphone Preamplifier with 20dB Gain
is the output impedance of the microphone, and G is
FIGURE 6. Improved Ripple Rejection
(Continued)
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POT
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can
9
6.0 Adjustable-Gain Amplifier
The LMV101/102/105/110 not only provides fixed gain of −1,
−2, −5, and −10, it can also be configured for different gains
by adding only one external resistor.
You can decrease the gain by putting a resistor in series with
pin 1 ( Figure 7 ). You can increase the gain by connecting a
resistor from pin 1 to pin 3 ( Figure 8 ).
If you are using the LMV110 as a microphone preamplifier
for an electret microphone ( Figure 5 ), and the output imped-
ance of the microphone is 1k , then the gain of the pream-
plifier is
If we choose a small value for R, then we could get a pream-
plifier with a gain close to 100 (40dB), which is 10 times the
gain provided by LMV110.
FIGURE 7. Decreased Gain
FIGURE 8. Increased Gain
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