Datasheet

100
1k
10k
100k 400k
FREQUENCY (Hz)
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
GAIN (dB)
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 =
LMV771, LMV772, LMV774
www.ti.com SNOSA04F –MAY 2004–REVISED SEPTEMBER 2010
(26)
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:
(27)
or
R
5
= 10R
6
R
6
= 1.5kΩ R
5
= 15kΩ (28)
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:
The frequency responses of each stage of the state variable active filter when implemented with the LMV774 are
shown in the following figures:
Figure 14. Lowpass Filter Frequency Response
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