LT1366/LT1367
LT1368/LT1369
16
1366fb
the 2 op amp loop to create a negative summing junction
at A1’s positive input
1
. The circuit has low sensitivities for
center frequency and Q, which are set with the following
equations:
ω
0
2
= 1/(R1 • C1 • R2 • C2)
where:
R1 = 1/(ω
0
• Q • C1) and R2 = Q/(ω
0
• C2).
The DC bias applied to A2 and A4, half supply, is not needed
when split supplies are available. The circuit swings rail-
to-rail in the passband making it an excellent anti-aliasing
filter for ADCs. The amplitude response is flat to 1kHz then
rolls off at 80dB/decade.
Typical applicaTions
1
James Hahn, “State Variable Filter Trims Predecessor’s Component Count,” Electronics, April
21, 1982.
FREQUENCY (Hz)
100
–80
GAIN (dB)
–60
–40
–20
0
–144
–72
0
72
180
144
108
36
–36
–108
–180
1k 10k
1366 F09
PHASE (DEG)
GAIN
PHASE
V
OUT
10k
V
+
2
3
5
6
7
V
IN
1
22pF
1M
1M
SIGNAL AMP
CANCELLATION AMP
–
+
–
+
1/2 LT1366
1/2 LT1366
1366 F10
R
P
10k
R
L
V
CC
–
+
1/2 LT1366
1366 F11
Figure 10. Input Bias Current Cancellation
Figure 9. Frequency Response of 4th Order Butterworth Filter Figure 11. Rail-to-Rail Potentiometer Buffer
