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03 | Keysight | Photodiode Test Using the Keysight B2980A Series - Technical Overview
Photodiode Characterization Example
This section explains how to perform PD dark current measurements using the B2985A/87A.
Test System
Figure 1 shows the circuit diagram to evaluate PD characteristics using the B2985A/87A
Electrometer/High Resistance Meter. The B2985A/87A's voltage source high terminal is
connected to the cathode of the PD to supply a reverse bias voltage, and its ammeter is
connected to the anode of the PD to measure the PD current. The voltage source's low
terminal and the ammeter common are connected together internally.
High
PD
Ammeter
Input
Figure 1. Circuit diagram to evaluate photodiode characteristics
Since the B2985A/87A's voltage source has the capability to sweep voltage while its
ammeter synchronously measures current, the PD's current – voltage (IV) characteristics
can easily be obtained. In addition, the B2985A/87A's ability to display the results as an
X-Y graph permits quick examination of the results.
The following example will show how to make a silicon photodiode dark current
measurement. The key measurement parameters are summarized in Table 1. The PD current
is measured by the B2985A/87A's ammeter as the B2985A/87A's voltage source applies a
reverse-bias voltage. The voltage is swept from 10 mV to 5 V in 10 mV steps. A fixed range
of 20 pA range is used to measure the PD current since the maximum expected current is
several picoamps, and using the 20 pA range provides better accuracy. The measurement
trigger delay time is set at 1 s to give the measured current sufficient time to stabilize.
Of course, since the dark current measurement has to be made without light the PD is
tested in an enclosed test fixture.
Table 1. Photodiode characterization key measurement conditions
B2985A/87A
Parameters
PD Voltage Swept
Start
Stop
Points
PD Current
Range
Aperture Time (SPEED)
Trigger
Source
Count
Measure Delay
Period
B2985A/87A
-
A
+
Values
10 mV
5 V
500
20 pA Fixed
Normal
AUTO
500
1 s
1.2 s
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