Datasheet

10k
100k 1M 10M
FREQUENCY (Hz)
-40
-30
-20
-10
0
10
20
GAIN (dB)
C
F
= 0 pF
C
F
= 5 pF
C
F
= 2 pF
R
1
, R
2
= 30 k:
A
V
= -1
10k
100k 1M 10M 100M
FREQUENCY (Hz)
-25
-20
-15
-10
-5
0
5
10
15
GAIN (dB)
R
1,
R
2
= 30 k:
A
V
= -1
R
1,
R
2
= 10 k:
R
1,
R
2
= 1 k:
LMV791, LMV792
SNOSAG6F –SEPTEMBER 2005–REVISED MARCH 2013 www.ti.com
Figure 52. Gain Peaking Caused by Large R
1
, R
2
A way of reducing the gain peaking is by adding a feedback capacitance C
F
in parallel with R
2
. This introduces
another pole in the system and prevents the formation of pairs of complex conjugate poles which cause the gain
to peak. Figure 53 shows the effect of C
F
on the frequency response of the circuit. Adding a capacitance of 2 pF
removes the peak, while a capacitance of 5 pF creates a much lower pole and reduces the bandwidth
excessively.
Figure 53. Gain Peaking Eliminated by C
F
AUDIO PREAMPLIFIER WITH BANDPASS FILTERING
With low input referred voltage noise, low supply voltage and low supply current, and a low harmonic distortion,
the LMV791 family is ideal for audio applications. Its wide unity gain bandwidth allows it to provide large gain for
a wide range of frequencies and it can be used to design a preamplifier to drive a load of as low as 600Ω with
less than 0.01% distortion. Two amplifier circuits are shown in Figure 54 and Figure 55. Figure 54 is an inverting
amplifier, with a 10 kΩ feedback resistor, R
2
, and a 1kΩ input resistor, R
1
, and hence provides a gain of −10.
Figure 55 is a non-inverting amplifier, using the same values of R
1
and R
2
, and provides a gain of 11. In either of
these circuits, the coupling capacitor C
C1
decides the lower frequency at which the circuit starts providing gain,
while the feedback capacitor C
F
decides the frequency at which the gain starts dropping off. Figure 56 shows the
frequency response of the inverting amplifier with different values of C
F
.
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