Tektronix ADA400A

The ADA400A Differential Preamplifier allows direct oscilloscope measurements of very low amplitude voltages and signals which are not ground referenced. The high impedance of both inputs eliminates the need to add additional ground points in the DUT, thereby avoiding circulating currents which disturb the measurement or the circuit. Typically 100 dB CMRR DC to 10kHz Integral Probe Power with TEKPROBE BNC Powered directly from TDS400, TDS500, TDS600, and TDS700 Series oscilloscopes

Tektronix ADA400A datasheet & specifications