
LT1366/LT1367
LT1368/LT1369
1366fb
the 2 op amp loop to create a negative summing junction
at A1’s positive input1. The circuit has low sensitivities for
center frequency and Q, which are set with the following
equations:
ω02 = 1/(R1 C1 R2 C2)
where:
R1 = 1/(
ω0 Q C1) and R2 = Q/(ω0 C2).
TheDCbiasappliedtoA2andA4,halfsupply,isnotneeded
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
1James 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
VOUT
10k
V+
2
3
5
6
7
VIN
1
22pF
1M
SIGNAL AMP
CANCELLATION AMP
–
+
–
+
1/2 LT1366
1366 F10
RP
10k
RL
VCC
–
+
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