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DA18000AC Differential Amplifier
USE OF DC ÷2 ATTENUATOR
The ÷2 attenuator should be used when the common mode or differential voltage of the cir-
cuit under test is unknown or exceeds the maximum voltage specified. (See section 9, Spec-
ifications). The use of the attenuator will also reduce the reflections, thus improving the
VSWR.
The DA18000AC amplifier has no method to detect the presence or absence of the attenua-
tor. To maintain correct vertical scale factor and amplitude measurement results, you must
inform the oscilloscope when the attenuator is being used. This is done in the Vertical
Adjust → DA18000AC control dialog for the channel that the amplifier is connected to.
GROUNDING
In most cases, when the common mode portion of the signal consists mainly of lower fre-
quencies, the amplifier does not need to be connected to ground of the circuit under test.
This will minimize the effects of ground loop currents. Any signal corruption caused by not
having the amplifier connected to ground of the signal under test will be common to both
inputs and will be rejected by the differential operation of the amplifier.
However when working in an environment with high RF ambient noise, it may be better to
connect the amplifier ground lead to a good RF ground near the point where the signal is
being measured. To find out if a ground lead is necessary, make a measurement with and
without a ground lead and use the one that gives the least signal corruption.
The cables attached to the DA18000AC amplifier are always grounded to the oscilloscope
and to earth ground through the power line cable.
DYNAMIC RANGE
The DA18000AC amplifier has no gain or attenuation control. The system gain is fixed at x1.
The DA18000AC amplifier is always AC coupled. However exceeding the common mode
range may introduce distortion to the output signal. Use of the ÷2 attenuators will increase
the differential mode range; however, due to power limitations, they will not increase the
common mode range.
There are two common mode voltages:
±10 V without a ÷2 attenuator
with a ÷2 attenuator
7 V
rms
4-4
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DA18000AC-OM-E Rev A
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