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MT-Lab - Application Note #01
02/10/2015
Impedance analysis with an external DC Bias
I – Introduction
With direct connections to sample a MTZ-35
system provides wide bandwidth ac
impedance measurements in the presence of
dc component but the dc component cannot
exceed the internal generator level of +/- 10V
dc.
In order to make impedance measurements
in the presence of a larger dc level, it is
necessary to use an external circuit that will
block the dc component from the
measurement instrument while allowing the
ac component to be measured.
The following diagram illustrates a circuit
that provide dc blocking, a capacitor
discharge path and DC source resistance. DC
voltages up to the rated voltage of the
capacitors can now be used.
The recommended component values in this
circuit are appropriate for a Sample Under
Test that exhibits an impedance less than
10MΩ over the test frequencies being used.
It is important to remember that open/short
circuit sweep compensation should be
applied in order to minimize the effect of the
test circuit on impedance measurement
results.
Fig. 1 : Electronic schematic
Bio-Logic Science Instruments, 1 Rue de l'Europe, 38640 Claix, FRANCE
Tel: +33 476 98 68 31 – Fax: +33 476 98 69 09 www.bio-logic.info
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