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2 – 2
2.1 General
2.2 Required Equipment
2.3 High Frequency Compensation
The purpose of calibration is to verify operation of the unit and to:
Adjust the high frequency compensation for best pulse re-
sponse.
Adjust the offset to null the DC voltage at the output with no
input.
Adjust the gain to 10
nominal gain for an amplifier driving a 50 Ω load will be 5
(+14dB).
Since the adjustments are interdependent, it is important that the
adjustments be done in the prescribed order, and that all of the ad-
justments be done. For example, adjusting the high frequency com-
pensation will affect the output offset.
1. Pulse generator, splitter and attenuator to produce
square waves with a rise time of less than 1ns. (DG535 Digital
Delay/Pulse Generator, AB output, into unmatched tee driv-
ing two 50 Ω cables with a 20 dB attenuator on the one that
goes to the SIM914.)
2. Digital multimeter with 4-wire ohm measurement capability
(Agilent 34401).
3. Oscilloscope with at least 300 MHz bandwidth.
The SIM914 uses an AD8009 current feedback amplifier in the out-
put stage. The gain of the amplifier is controlled by the ratio of re-
sistors in the feedback network and the bandwidth is controlled by
the Thevenin equivalent source impedance of the feedback network.
The ratio is fixed (by R115 & R116 or R215 & R216) to provide a
gain of 5 and the source impedance may be adjusted (by P102 and
P202).
The bandwidth is set to optimize the pulse response of the amplifier.
This is done by applying a fast pulse at the input and adjusting P102
(or P202 for Channel 2) so that the output rise time and overshoot
most closely match the rise time and overshoot of the fast input pulse
as observed on a 300 MHz oscilloscope with 50 Ω input impedance.
Note that adjusting P102 will affect the offset for Channel 1, as there
is a large input bias current (150 A max) to the inverting input of
for an unloaded output so that the
SIM914 350 MHz Preamplifier
Calibration
100 mV
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