Teledyne LeCroy AP034 - Manual (Page 35)

Operator’s Manual
922261-00 Rev A 29
B. Check High Frequency Common Mode Rejection Ratio (CMRR)
NOTE: Common Mode Rejection Ratio (CMRR) is defined as the Differential Mode Gain divided by
the Common Mode Gain (normalized inverse of the Common Mode response). At frequencies
below approximately 250 MHz, the bandwidth related attenuation in the AP034 Active Differential
Probe is so insignificant that the Differential Mode Gain can be assumed to be unity (1.0).
1. Disconnect the ProBus Extension cable from the AP034 and the oscilloscope. Reconnect the
AP034 directly to the Channel 1 input of the oscilloscope.
2. Carefully move the AP034 probe head from the Differential Drive No Termination connector of
the AP033/AP034 Calibration Fixture to the Common Mode Drive 50 ohm Termination
connector. Make sure that the probe is fully engaged in the fixture.
3. Set the oscilloscope to display channel 1. In the oscilloscope Channel 1 “COUPLING” menu, set
Coupling to DC 1 MΩ, and Global BWL to Off. Autobalance the AP034 by pressing the
AUTOBALANCE menu button twice. Set the oscilloscope trigger mode to AUTO.
4. If necessary, center the trace with the Probe Offset (channel O
FFSET
knob).
5. Connect a BNC cable from the output of the high frequency sine wave generator to the Channel
2 input of the oscilloscope.
6. Set the oscilloscope as follows:
Display Channel 2 only
Channel 2 VOLTS/DIV 0.5 V/div
Channel 2 Coupling DC 50Ω
Trigger on 2
Trigger coupling 2 HF
TIME/DIV 5 ns/div
Acquisition Mode NORMAL
7. Set the high-frequency sine wave generator frequency to 100 MHz, and the amplitude to
approximately 2 V
p-p
. Set the RF Output to ON.
8. Adjust the oscilloscope trigger level as needed for a stable display.
9. Adjust the output amplitude of the high frequency sine wave generator for a display of exactly
4 divisions (2 V) peak-topeak. Turn off the RF Output.