SIM918 Precision Current Preamplifier0 pages

Small Instrumentation Modules
SIM918 — Precision current preamplifier with autozero feature

· Input offset voltage <10 µV
· DC bias current <2 pA
· Current gain of 106 to 108 V/A
· 15 fA/√Hz input noise (108 V/A)
· Autozero feature
· Bias voltage input

· SIM918 ... $1250 (U.S. list)

SIM918 Precision Current Preamplifier
The SIM918 Current Preamplifier is ideal in applications in
which the input offset voltage must be kept to a minimum.
The DC voltage difference between the two inputs (current
input and voltage bias) is accurately measured every two
seconds, and is nulled. The result is a current amplifier with
less than 10 µV input offset voltage. This autozeroing feature
can be engaged or inhibited remotely or from the front panel,
giving you flexibility in sensitive applications.
As a current amplifier, the SIM918 offers input noise as low
as 15 fA/√Hz and adjustable current gain (106 to 108 V/A).
The output voltage range is ±10 V for all gain settings. Input
bias current is less than 2 pA (DC), and the instrument has up
to 22 kHz of (gain-dependent) bandwidth.
There is a voltage bias input for setting the virtual ground
potential to an external DC source. This input can range over
±5 V. The bias voltage can be internally grounded.

Stanford Research Systems

An autozero sync input/output connection is also provided.
In the internal autozeroing mode, this port provides a one
pulse-per-second (pps) output synchronous with the internal
switching circuitry. In the external mode, a 0.9 to 1.1 pps input
signal generates the reference for synchronizing the circuitry.
The SIM918 provides maximum flexibility for cabling and
grounding. The shield of the current input BNC can be
switched between chassis ground, the bias voltage, or the rearpanel Program input (which can be left floating, if desired).
With the Program input, a user can supply an excitation
potential to an experiment via the shield conductor of the
input cable, while the excited current flows through the center
conductor to the SIM918. The shield of the voltage bias BNC
can be independently grounded or floated.
The digital control circuitry in the SIM918 is designed
with SRS’s special clock-stopping architecture in which the
microcontroller is turned on only when settings are being

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