DA1855A Differential Amplifier
3-6
ISSUED: July 2002
DA1855A-OM-E Rev A
Note that while in
V
COMP
mode, the amplifier is configured for
single ended measurements. The –
INPUT
connector is not
usable when
V
COMP
is selected. The input signal applied to the
+
INPUT
is referenced to ground offset by the value set by the
Precision Voltage Generator. Large calibrated offsets can be
obtained while making differential measurements by using
V
DIFF
mode.
Precision Voltage Generator
The PVG generates the voltage which is used in the
V
COMP
and
V
DIFF
modes and appears at the rear panel
OFFSET VOLTAGE
(PVG) output connector for use as a reference voltage.
The Precision Voltage Generator (PVG) output range is
±
15.500
Volt. The PVG is never attenuated by the input attenuator.
Attenuation of the
+INPUT
signal by the
÷÷
10
input attenuator will
cause the PVG to null out an input voltage up to
±
155.00 Volt
which is ten times larger than the actual PVG voltage.
The increase in common mode voltage range also applies when
using attenuating probes.
When the DA1855A is used with attenuating probes that feature
readout, the PVG display is changed to indicate the voltage at the
+INPUT
probe tip which will bring the amplifier output to zero.
When connected to a LeCroy oscilloscope via the ProBus
interface, the oscilloscope
OFFSET
control increments or
decrements the PVG’s output voltage and the offset value will be
shown on the six PVG front panel indicators. The new offset
value will also be displayed on the oscilloscope’s screen for a few
seconds after a change has been made.
When connected to an oscilloscope not provided with a ProBus
interface, the PVG can be accessed by means of push buttons.
Above each digit is a push button which increments the
corresponding digit by one when pushed. When held, the digit
continues to increment, eventually incrementing the next higher
digit.
Similarly, below each digit is a push button which decrements the
corresponding digit.
The
±±
button above the left-most digit changes the PVG output
polarity. The
ZERO
button below the left-most digit sets the
output to zero and invokes the PVG's Auto Zero function.
