DA1855A Differential Amplifier
12
922258-00 Rev A
Front Panel
Input Connectors
Signals applied to the +INPUT and the –INPUT are connected either directly to the DA1855A
amplifier’s inputs or to the input attenuators. Maximum input voltage is ±200 Vp
A signal connected to the +INPUT will remain its polarity at the output connector. A signal
connected to the –INPUT will be inverted in polarity.
Attenuators
The input attenuators are passive networks which divide each signal by ten.
In ÷1 mode the front panel input connectors are directly connected to the DA1855A amplifier's
differential inputs.
In ÷10 mode each front panel input connector is connected to a passive 1 MΩ attenuator. The
attenuator output is connected to the DA1855A amplifier's corresponding differential input. The
signal at each input is attenuated by a factor of ten.
Gain
The DA1855A amplifier gain (amplification) is selectable between X1 and X10. The amplified signal
appears at the rear panel AMPLIFIER OUTPUT connector.
Gain will affect the differential mode output signal by amplifying the signal difference between the
+INPUT and the –INPUT, but will not affect the common mode signal, the signal common to the
+INPUT and them –INPUT.
Output Termination
Proper gain is obtained when the DA1855A drives a 50 Ω load such as an oscilloscope with input
impedance set to 50 Ω. Automatic 50 Ω termination is obtained when the DA1855A is connected to
a Teledyne LeCroy oscilloscope through the ProBus interface.
An instrument with only a 1 MΩ input impedance available should have a 50 Ω coaxial termination
placed on its input connector. The DA1855A is then connected to the oscilloscope through the
coaxial termination.
Input Resistance
When the input ATTENUATOR is set to ÷1 and no attenuating probe is connected, the input
resistance can be increased from 1 MΩ to 100 MΩ. This is advantageous when measuring high
impedance circuits or when AC coupling is needed with a very low frequency cut off. When the input
ATTENUATOR is set to ÷10 or an attenuating probe with read out capability is attached, 1 MΩ (1M)
input resistance is automatically selected.
Summary of Contents for DA1855A
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