Keithley 6485 User Manual

Model 6485 Picoammeter Instruction Manual Applications Guide I-23
mounts, etc.,), as well as a triggerable voltage source (the Model 2400 is used in our exam-
ple). Several Model 6485's can be connected to probe pads to provide leakage current
readings forced by the bias voltage source. As an alternative, one or more 6485s could be
switched through a switching mainframe and matrix switch card arrangement to take cur-
rent measurements from multiple pads.
Measuring photo diode leakage can be described in two steps:
1. V
sweep
, I
meas
in total darkness
2. V
bias
, I
meas
in calibrated optical flux
In the 1st step, voltage sweeps and the resulting current leakage is measured. Then, a bias
voltage is applied and resulting current leakage is measured while light is incrementally
increased in calibrated steps. The results produce a graph similar to Figure I-20.
Figure I-20
General photo diode leakage
P.I.N. (Positive Intrinsic Negative) diodes respond as shown in Figure I-21.
I
V
0
General photo diode

Keithley 6485 Specifications

General

Model	Keithley 6485
Category	Picoammeter
Input Impedance	>10^14 Ohms
Voltage Burden	<200µV
Accuracy	0.4% of reading
Voltage Source Range	Not Applicable
Voltage Source Resolution	Not Applicable
Voltage Source Accuracy	Not Applicable
Interface	IEEE-488
Power Requirements	100V to 240V AC, 50/60Hz
Dimensions	89 mm high x 214 mm wide x 369 mm deep (3.5 in x 8.4 in x 14.5 in)