Lecroy DA1855A Data Sheet

The DA1855A is a stand-alone,  
high-performance 100 MHz differential 
amplifier. It is intended to act as a  
signal conditioning preamplifier for  
oscilloscopes, digitizers and spectrum 
analyzers, providing differential 
measurement capability to instru-
ments having only a single-ended 
input. When used with a DA1855A, 
oscilloscopes can obtain Common 
Mode Rejection Ratio (CMRR) and 
overdrive recovery performance levels 
previously unobtainable.

Amplifier gain can be set to 1 or 10.  
A built-in input attenuator can 
be separately set to attenuate  
signals by a factor of 10, providing 
gains of 10, 1, or 0.1 and common 
mode dynamic range of ±15.5 V (÷1) 
or ±155 V (÷10). Optional probes 
increase the maximum input signal 
and common mode ranges in  
propor tion to their attenuation ratio but 
do not exceed their maximum input 
voltage rating. Effective gain of the 

DA1855A, including probe attenuation, 
amplifier gain and attenuator settings, 
is automatically displayed.

The DA1855A has a bandwidth of  
100 MHz, but any one of the three 
3-pole bandwidth limit filters can be 
selected to reduce bandwidth to  
20 MHz, 1 MHz or 100 kHz to limit 
noise above the frequency of interest.

The DA1855A output is carefully 
limited to ±500 mV, so that the 
oscilloscope is not overdriven by large 
inputs. This allows many oscilloscopes 
to directly measure the settling of 
D/A converters with 14-bit (60 ppm) 
precision, better than any other 
differential comparator.

The DA1855A features a built-in 
Precision Voltage Generator (PVG) 
that can be set to any voltage between 
±15.5 V (±10 V in Differential Offset) 
with up to 100 µV resolution. The PVGs 
output can be selected as an input to 
the inverting (-) input of the amplifier 

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