Datasheet

LM4765
www.ti.com SNAS030C –AUGUST 1998–REVISED APRIL 2013
Thus with R
i
= 1 kΩ a non-inverting gain of 21 will result. Since the desired input impedance was 47 kΩ, a value
of 47 kΩ was selected for R
IN
. The final design step is to address the bandwidth requirements which must be
stated as a pair of −3 dB frequency points. Five times away from a −3 dB point is 0.17 dB down from passband
response which is better than the required ±0.25 dB specified. This fact results in a low and high frequency pole
of 4 Hz and 100 kHz respectively. As stated in the External Components section, R
i
in conjunction with C
i
create
a high-pass filter.
C
i
≥ 1/(2π * 1 kΩ * 4 Hz) = 39.8 μF; use 39 μF. (9)
The high frequency pole is determined by the product of the desired high frequency pole, f
H
, and the gain, A
V
.
With a A
V
= 21 and f
H
= 100 kHz, the resulting GBWP is 2.1 MHz, which is less than the ensured minimum
GBWP of the LM4765 of 5 MHz. This will ensure that the high frequency response of the amplifier will be no
worse than 0.17 dB down at 20 kHz which is well within the bandwidth requirements of the design.
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