LMV101 National Semiconductor Corporation, LMV101 Datasheet - Page 8

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

www.national.com
Application Information
3.0 Capacitive Load Tolerance
The LMV101/102/105/110 can directly drive 200pF capaci-
tive load with Vs = 5V at −1 gain configuration without oscil-
lation. Direct capacitive loading reduces the phase margin of
amplifiers. The combination of the amplifier’s output imped-
ance and the capacitive load induces phase lag. This results
in either an underdamped pulse or oscillation. To drive a
heavier capacitive load, a resistive isolation can be used as
shown in Figure 1 .
The isolation resistor R
stability by adding more phase margin to the overall system.
The desired performance depends on the value of R
bigger the R
Figure 2 is an output waveform of Figure 1 using 100
R
4.0 Phase Inverting AC Amplifier
A single supply phase inverting AC amplifier can be easily
built with the LMV101/102/105/110 series ( Figure 3 ). The
output voltage is biased at mid-supply, and AC input signal is
amplified by (R
pling capacitor to block DC potentials. A capacitor of 0.1µF or
iso
FIGURE 1. Resistive Isolation of a Heavy Capacitive
FIGURE 2. Pulse Response of LMV101 in Figure 1
and 1000pF for C
iso
2
resistor value, the more stable V
/R
1
). Capacitor C
L
iso
.
and the C
Load
IN
L
acts as an input AC cou-
form a pole to increase
(Continued)
DS101234-13
OUT
iso
will be.
. The
for
DS101234-12
8
larger can be used. The output can swing rail-to-rail. To avoid
output distortion, the peak-to-peak amplitude of the input AC
signal should be less than V
It is recommended that a small-valued capacitor be used
across the feedback resistor (R
lems, prevent peaking of the response, and limit the band-
width of the circuit. This can also help to reduce high fre-
quency noise and some other interference. (See Figure 4 )
5.0 Microphone preamplifier
Most microphones have a low output voltage level. This out-
put signal needs to be amplified so that it can feed the next
stage with optimal level. Figure 5 shows a microphone
preamplifier circuit with the LMV110. This microphone
preamplifier can provide 20dB gain. It can be implemented in
PCs, PDAs, and mobile phones.
Input capacitor C
blocks any DC voltage from the previous stage to prevent
the output from shifting to some unwanted DC level. This
could cause the output to saturate when audio signal is ap-
plied at the input. Second, the C
form a low pass filter to block any low frequency noise. The
cut-off frequency of this low pass filter is given by,
where R
to block the DC output from the next stage. R
according to the microphone requirement.
FIGURE 3. Phase Inverting AC Amplifier
1
= 10k in LMV110. Output capacitor C
IN
serves two important functions. First, it
FIGURE 4.
CC
(R
2
IN
) to eliminate stability prob-
1
and the 10k input resistor
/R
2
).
bias
DS101234-10
DS101234-11
OUT
is selected
is used