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Analog Engineer's Circuit
Photodiode Amplifier Circuit
Design Goals
Input Output BW Supply
IiMin IiMax VoMin VoMax fp Vcc Vee Vref
0A 2.4 µA 100 mV 4.9 V 20 kHz 5V 0V 0.1 V
Design Description
This circuit consists of an op amp configured as a transimpedance amplifier for amplifying the light-dependent
current of a photodiode.
Design Notes
1. A bias voltage (Vref) prevents the output from saturating at the negative power supply rail when the input
current is 0 A.
2. Use a JFET or CMOS input op amp with low bias current to reduce DC errors.
3. Set output range based on linear output swing (see Aol specification).
SBOA220A – JANUARY 2018 – REVISED FEBRUARY 2019 Photodiode Amplifier Circuit 1
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Design Steps
1. Select the gain resistor.
V − VoMin
R1 = oMax
IiMax = 4 . 9V − 0 . 1V
2 . 4μA = 2MΩ
2. Select the feedback capacitor to meet the circuit bandwidth.
C1 ≤ 2 × π ×1R × f
1 p
1
C1 ≤ 2 × π × 2MΩ × 20kHz ≤ 3 . 97pF ≈ 3 . 3pF (Standard Value)
3. Calculate the necessary op amp gain bandwidth (GBW) for the circuit to be stable.
Ci + C1 20pF + 3 . 3pF
GBW > > 2 > 170kHz
2 × π × R1 × C12 2 × π × 2MΩ × 3 . 3pF
where Ci = Cj + Cd + Ccm = 11pF + 5pF + 4pF = 20pF given
• Cj: Junction capacitance of photodiode
• Cd: Differential input capacitance of the amplifier
• Ccm: Common-mode input capacitance of the inverting input
4. Calculate the bias network for a 0.1 V bias voltage.
V −V
R2 = ccV ref × R3
ref
R2 = 5V0−. 1V
0 . 1V
× R3
R2 = 49 × R3
Closest 1% resistor values that yield this relationship are
R2 = 13 . 7kΩ and R3 = 280Ω
5. Select C2 to be 1 µF to filter the Vref voltage. The resulting cutoff frequency is:
1 1
fp = = = 580Hz
2 × π × C2 × R2 ∥ R3 2 × π × 1 μF × 13 . 7k ∥ 280
2 Photodiode Amplifier Circuit SBOA220A – JANUARY 2018 – REVISED FEBRUARY 2019
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Design Simulations
DC Simulation Results
AC Simulation Results
SBOA220A – JANUARY 2018 – REVISED FEBRUARY 2019 Photodiode Amplifier Circuit 3
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Revision History www.ti.com
Design References
See Analog Engineer's Circuit Cookbooks for TI's comprehensive circuit library.
See the circuit SPICE simulation file SBOC517.
See TIPD176.
Design Featured Op Amp
OPA322
Vcc 1.8 V to 5.5 V
VinCM Rail–to–rail
Vout Rail–to–rail
Vos 0.5 mV
Iq 1.6 mA/Ch
Ib 0.2 pA
UGBW 20 MHz
SR 10 V/µs
#Channels 1, 2, and 4
OPA322
Design Alternate Op Amp
LMP7721
Vcc 1.8 V to 5.5 V
VinCM Vee to (Vcc –1 V)
Vout Rail–to–rail
Vos 26 µV
Iq 1.3 mA/Ch
Ib 3 fA
UGBW 17 MHz
SR 10.43 V/µs
#Channels 1
LMP7721
Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from February 1, 2018 to February 4, 2019 Page
• Downscale the title and changed title role to 'Amplifiers'. Added links to circuit cookbook landing page and
SPICE simulation file.......................................................................................................................................... 1
4 Photodiode Amplifier Circuit SBOA220A – JANUARY 2018 – REVISED FEBRUARY 2019
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