參數資料
型號: LMV102M7
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 運算放大器
英文描述: Fixed-Gain Amplifiers
中文描述: OP-AMP, PDSO5
封裝: SC-70, 5 PIN
文件頁數: 10/12頁
文件大?。?/td> 769K
代理商: LMV102M7
Application Notes
(Continued)
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
can
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
is the output impedance of the microphone, and G is
the gain of the preamplifier in absolute value.
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.
DS101234-15
FIGURE 5. Microphone Preamplifier with 20dB Gain
DS101234-17
FIGURE 6. Improved Ripple Rejection
DS101234-18
FIGURE 7. Decreased Gain
DS101234-19
FIGURE 8. Increased Gain
L
www.national.com
10
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