Teledyne LeCroy AP034 - Manual (Page 21)

Operator’s Manual
922261-00 Rev A 15
NOTE: Probe offset is controlled with the channel OFFSET knob in oscilloscope firmware versions
8.1.0 or higher (including X-Stream firmware). The current offset value is displayed above the
graticule for a few seconds after a change is made by turning the knob. In prior software versions,
the channel OFFSET knob adjusted the offset of the oscilloscope input rather than the probe offset.
When the AP034 Active Differential Probe is used with Teledyne LeCroy oscilloscopes with older
software versions, it is important that the channel offset (controlled by the channel OFFSET knob)
remain set to 0.0000 V. Moving the displayed waveform with the channel offset rather than probe
offset will not re-center the dynamic operating range of the probe. Offsetting the trace with the
oscilloscope channel offset introduces the possibility of erroneous waveforms that result from
overloading the probe.
Autobalance
The AP034 Active Differential Probe incorporates an Autobalance function to remove the DC offset
from the output. Autobalance must be invoked by you. When power is first applied, the probe will
return to the internal values resulting from the last Autobalance cycle. For Autobalance to function
properly, all signals must be removed from the input.
After several minutes of warmup, or when the probe is exposed to a large shift in ambient
temperature, some DC offset drift may occur from thermal effects in the amplifier circuitry. To
initiate an Autobalance cycle, remove the probe from the test circuit and select the AUTOBALANCE
menu selection in the oscilloscope “COUPLING” menu for the channel the probe is connected to. If
the probe is being used with the ADPPS power supply, remove the input signal, then push and hold
both OFFSET buttons for two seconds. The AP034 must be terminated into 50Ω for successful
Autobalance.
Upon successful completion of the Autobalance cycle, all three of the EFFECTIVE GAIN indicators
will be briefly illuminated. If an input signal is present during auto balance and the routine fails, the
EFFECTIVE GAIN indicators will not illuminate. The probe will then revert to the offset values
resulting from the last. successful completion of the Autobalance cycle. In many situations, this will
be adequate to make routine measurements.
Designing Test Fixtures for the AP034 Probe
Often it is desirable to connect the probe directly to user fabricated test fixtures, such as those
used for semiconductor characterization. To facilitate use with custom test fixtures, the input
receptacles of the AP034 probe are compatible with commercially available 0.025 in. (0.635 mm)
square pins. The receptacles do not require a specific rotational alignment for the square pin. The
dimensions listed below can be used as a layout guide for a test fixture circuit board. The
recommended insertion depth of the pins is 0.100 in. (2.5 mm) to 0.200 in. (5.0 mm).