Datasheet

DC GAIN =
R
5
+ R
6
R
6
R
1
+ R
4
R
1
= -14.8 dB
Q =
11
2
=
1
2
R
5
+ R
6
R
6
Z
c
=
C
2
R
2
1
C
2
C
3
R
2
R
3
C
3
R
3
R
5
+ R
6
R
6
R
1
R
1
+ R
4
and
Q =
SM73308
www.ti.com SNOSB90B –JUNE 2011–REVISED APRIL 2013
The center frequency and Quality Factor for all of these filters is the same. The values can be calculated in the
following manner:
(25)
A design example is shown here:
Designing a bandpass filter with center frequency of 10kHz and Quality Factor of 5.5
To do this, first consider the Quality Factor. It is best to pick convenient values for the capacitors. C
2
= C
3
=
1000pF. Also, choose R
1
= R
4
= 30kΩ. Now values of R
5
and R
6
need to be calculated. With the chosen values
for the capacitors and resistors, Q reduces to:
(26)
or
R
5
= 10R
6
R
6
= 1.5kΩ R
5
= 15kΩ (27)
Also, for f = 10kHz, the center frequency is ω
c
= 2πf = 62.8kHz.
Using the expressions above, the appropriate resistor values will be R
2
= R
3
= 16kΩ.
The following graphs show the transfer function of each of the filters. The DC gain of this circuit is:
(28)
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