Photodiode Current (uA)
OA
V
o
lta
g
e
Ou
tp
u
t (V
)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0
0.5
1
1.5
2
2.5
3
3.5
D002
Input Current (A)
V
o
lta
g
e
(
V
)
0
5E-7
1E-6
1.5E-6
2E-6
0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
2.7
3
3.3
3.6
3.9
D001
F
OUT
PK
F
F
R
V
I
1
SC R
= -
´
+
Hardware Description
www.ti.com
The transfer function of the output is then seen in
Equation 3
:
(3)
As mentioned in the previous section, the TIDM-TIA has a feedback resistor with a resistance of 2.37 M
Ω
.
This combination of photodiode, feedback resistor, and op-amp should provide the ideal output voltage
seen in SPICE simulations in
Figure 5
. Currents created by the photodiode range from 0 to
−
1.5 µA, which
are used as test values.
Figure 5. TIA SPICE Simulation
The Tina-TI SPICE model of the op-amp is available on the MSP430F2274 product web page.
Characterization data for the photodiode current versus op-amp output voltage can be seen in
Figure 6
.
Results are close to expected output.
NOTE:
This output will change if using an external feedback resistor or different photodiode.
Figure 6. Op-Amp Voltage Output Characterization
For more information on the characteristics of the operational amplifier, see the
MSP430F2274 datasheet
.
6
MSP430F2274 Transimpedance Amplifier (TIDM-TIA) User's Guide
TIDU443 – August 2014
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