1.1kΩ
1.43kΩ
330pF
dc Gain = 1
2.2nF
1.1kΩ
1.65kΩ
VIN
1.43kΩ
1.91kΩ
OPA227
33nF
2.21kΩ
VOUT
10nF
OPA227
68nF
fN = 13.86kHz
Q = 1.186
fN = 20.33kHz
Q = 4.519
f = 7.2kHz
FIGURE 14. Three-Pole, 20kHz Low Pass, 0.5dB Chebyshev Filter.
20pF
0.1µF
TTL INPUT GAIN
9.76kΩ
“1”
“0”
+1
–1
100Ω
100kΩ
Balance
Trim
500Ω
2
3
Output
10kΩ
Input
6
2
3
OPA227
Output
6
8
4.99kΩ
OPA227
D1
D2
NOTE: Use metal film resistors
and plastic film capacitor. Circuit
must be well shielded to achieve
low noise.
S1
S2
Dexter 1M
Thermopile
Detector
1
4.75kΩ
4.75kΩ
1kΩ
Responsivity ≈ 2.5 x 104V/W
Output Noise ≈ 30µVrms, 0.1Hz to 10Hz
TTL
In
DG188
Offset
Trim
+VCC
FIGURE 16. High Performance Synchronous Demodulator.
FIGURE 15. Long-Wavelength Infrared Detector Amplifier.
OPA227, 2227, 4227
OPA228, 2228, 4228
16
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