Agilent Technologies B1500A Training Manual page 96

Gummel Plot
What is measured?
Ve is swept while Vb and Vc are held at 0 V
Ib and Ic are plotted on log scale
Constant
SMU3
The "Gummel Plot" is an excellent low current measurement to make on a bipolar transistor. It plots
log base current and log collector current against the same bias voltage. A good bipolar device has
constant gain over a wide bias range (both curves are linear and parallel). Low level base and
collector currents can be measured to the fA level on small signal devices.
Above, we see the simplest channel definition for making a Gummel plot. The emitter is swept from
ground to a negative value on a NPN device. Another method would be to hold Ve at 0 V while
synchronously sweeping Vb and Vc in a positive direction. In the later case, Vb could be the
primary sweep VAR1, and Vc could be the synchronous sweep VAR1'.
Collector
Base
Emitter
VAR1
SMU2
6-24
Constant
SMU4
Module 6
Low Current Measurement