Calibration; Getting Ready; O Set Voltage And Input Bias Current - Stanford Research Systems SIM954 Operation And Service Manual

300 mhz dual inverting driver amplifier

Table of Contents

4 Calibration

4.2 Offset Voltage and Input Bias Current

The SIM954 comes fully calibrated and should not exhibit major

deterioration of its properties under normal operating conditions.

The user can, however, re-calibrate the module with relative easy

and without excessive risk of degrading or damaging the product.

The required test equipment to trim the o set voltage and current of

the SIM954 is a voltmeter with 0.1 mV resolution.

Each of the two independent ampliﬁers of the SIM954 has one o set

voltage and one input bias current trimmer. They can be accessed by

removing the (right) side panel of the module which is on the side

closest to the front panel LEDs.

The o set voltage and bias current trimmers R117, R198, R121 and

R199 are located on the sparsely populated side of the PCB next to

the two power supply limiter heat sinks. They have the following

functions:

R117 - o set voltage compensation channel 1

R198 - input bias current compensation channel 1

R121 - o set voltage compensation channel 2

R199 - input bias current compensation channel 2

Since the input bias current is di cult to measure, the procedure

trims the (proportional) input o set voltage instead.

Step 1: Start by connecting a mV-meter to the input of channel 1. The

input o set voltage is then trimmed to 0mV with R117.

Step 2: After connecting the mV-meter to the output of channel 1, the

output o set voltage can be trimmed to 0 mV with R198.

Iteration: Steps 1 and 2 are repeated as many times as necessary to

trim both input and output o set voltage simultaneously to near 0 mV.

The same procedure is carried out for the second channel:

4 – 1

Table of Contents

Table of Contents