Texas Instruments | Dual-supply, discrete, programmable gain amplifier circuit | Application notes | Texas Instruments Dual-supply, discrete, programmable gain amplifier circuit Application notes

Texas Instruments Dual-supply, discrete, programmable gain amplifier circuit Application notes
Analog Engineer's Circuit: Amplifiers
SBOA232 – December 2018
Dual-supply, discrete, programmable gain amplifier circuit
Design Goals
Input
Output
Supply
ViMin
ViMax
VoMin
VoMax
Vcc
Vee
–1.25V
+1.25V
–2.4V
+2.4V
+2.5V
–2.5V
Gain
Cutoff Frequency
6dB (2V/V) to 60dB (1000 V/V)
7kHz
Design Description
This circuit provides programmable, non-inverting gains ranging from 6dB (2V/V) to 60dB (1000V/V) using
a variable input resistance. The design maintains the same cutoff frequency over the gain range.
C1 220p
V+
R2 100k
Vcc 2.5
VR3 100
R1
0 ± 100k
+
+
Vo
U1 OPA364
+
Vee 2.5
Vi
V+
V-
Design Notes
1. Choose a digital potentiometer, such as TPL0102 for R1 to design a low-cost digital programmable
gain amplifier.
2. R3 sets the maximum gain when R1 approaches 0Ω.
3. A feedback capacitor limits the bandwidth and prevent stability issues.
4. Stability should be evaluated across the selected gain range. The minimum gain setting will likely be
most sensitive to stability issues.
5. Some digital potentiometers can vary in absolute value by as much as +/-20% so gain calibration may
be necessary.
SBOA232 – December 2018
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Dual-supply, discrete, programmable gain amplifier circuit
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Design Steps
1. Choose R2 and R3, to set the maximum gain when R1 approaches 0:
2. Choose the potentiometer maximum value to set the minimum gain:
3. Choose the bandwidth with a feedback capacitor:
4. Check for stability at minimum gain (2V/V), which is when R1=100kΩ. To satisfy the requirement fc
(circuit bandwidth) must be less than fzero (zero created by the resistive feedback network and the
differential and common-mode input capacitances).
2
Dual-supply, discrete, programmable gain amplifier circuit
Copyright © 2018, Texas Instruments Incorporated
SBOA232 – December 2018
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Design Simulations
Transient Simulation Results
2.00m
T
Vi
Vo[1]
-1.53
1.47
Vo[2]
Vo[3]
Vo[4]
Vo[5]
Vo[6]
Vi
Vo[1]
Vo[2]
Vo[3]
Vo[4]
Vo[5]
Vo[6]
-2.00m
1.60
0[Ohm]
10[Ohm]
100[Ohm]
1k[Ohm]
10k[Ohm]
100k[Ohm]
-1.41
861.48m
-844.84m
167.68m
-166.85m
20.16m
-20.08m
3.78m
-3.77m
0.00
500.00u
Time (s)
1.00m
AC Simulation Results
T
60
Vo[1]
Vo[2]
Vo[3]
Vo[4]
Vo[5]
Vo[6]
Gain (dB)
40
0[Ohm]
10[Ohm]
100[Ohm]
1k[Ohm]
10k[Ohm]
100k[Ohm]
20
0
-20
10
SBOA232 – December 2018
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100
1k
10k
100k
Frequency (Hz)
1MEG
10MEG
100MEG
Dual-supply, discrete, programmable gain amplifier circuit
Copyright © 2018, Texas Instruments Incorporated
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References:
1. Analog Engineer's Circuit Cookbooks
2. SPICE Simulation File SBOC521
3. TI Precision Designs TIPD204
4. TI Precision Labs
Design Featured Op Amp
OPA364
Vss
1.8V to 5.5V
VinCM
Rail-to-rail
Vout
Rail-to-rail
Vos
1mV
Iq
1.1mA
Ib
1pA
UGBW
7MHz
SR
5V/μs
#Channels
1, 2, 4
www.ti.com/product/opa364
Design Alternate Op Amp
OPA376
Vss
2.2V to 5.5V
VinCM
Rail-to-rail
Vout
Rail-to-rail
Vos
5μV
Iq
760μA
Ib
0.2pA
UGBW
5.5MHz
SR
2V/μs
#Channels
1, 2, 4
www.ti.com/product/opa376
4
Dual-supply, discrete, programmable gain amplifier circuit
Copyright © 2018, Texas Instruments Incorporated
SBOA232 – December 2018
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