Datasheet
SLOS327C − AUGUST 2000 − REVISED MAY 2001
14
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
input resistance
Each gain setting is achieved by varying the input resistance of the amplifier, which can range from its smallest
value to over six times that value. As a result, if a single capacitor is used in the input high-pass filter, the −3 dB
or cutoff frequency will also change by over six times.
C
IN
R
I
R
f
Input Signal
The −3-dB frequency can be calculated using equation 1.
(1)
f
–3 dB
+
1
2p CR
I
input capacitor, C
I
In the typical application an input capacitor (C
I
) is required to allow the amplifier to bias the input signal to the
proper dc level for optimum operation. In this case, C
I
and the input impedance of the amplifier (Z
I
) form a
high-pass filter with the corner frequency determined in equation 2.
f
c(highpass)
+
1
2pZ
I
C
I
−3 dB
f
c
(2)
The value of C
I
is important to consider as it directly affects the bass (low frequency) performance of the circuit.
Consider the example where Z
I
is 710 kΩ and the specification calls for a flat-bass response down to 45 Hz.
Equation 2 is reconfigured as equation 3.
C
I
+
1
2p Z
I
f
c
(3)