Lecroy AP034-OM-E-03 User Manual
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The input circuits in the AP034 Activ e Differ ential
Probe incorporate components that protect the
probe from damage resulting from electrostatic
discharge (ESD). Keep in mind that this is an
active probe, and it should be handled carefully
to avoid damage. When using the AP034 Active
Differential Probe, you are advised to take
precautions against potential instrument damage
due to ESD.
CONNECTING THE PROBE TO THE TEST INSTRUMENT
When you are using the AP034 Active Dif ferential Probe with a
LeCroy Oscilloscope equipped with ProBus, attach the probe
output connector to the oscilloscope input connector. The
oscilloscope will recognize the probe, set the oscilloscope input
termination to 50 DQG DFWLYDWH WKH SUREH FRQWURO IXQFWLRQV LQ
the user interface.
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Caution
To use the AP034 Active Differ ential Probe with instrumentation
not equipped with a ProBus interface, it is necessar y to use the
ADPPS Power Supply. Attach the ADPPS connector to the probe
output connector. The output connector of the ADPPS is a
standard male BNC that can be directly connected to another
instrument. If necessary, the output of the ADPPS can be
interconnected with a 50 FRD[LDOFDEOH7RPLQLPL]HWKHHIIHFWV
of skin loss, this cable should be 1 m or less in length. The
AP034 Active Differential Probe is des igned to drive a 50 ORDG
The gain will be uncalibrated if the output is not correctly
terminated. If you are using the probe with an instrument with a
high input impedance, place a 50 %1&LQOLQHWHUPLQDWRURQWKH
instrument input before attaching the ADPPS.
CONNECTING THE PROBE TO THE TEST CIRCUIT
At the probe tip, two inputs and a ground connection are
available for connecting the probe to a circuit under test. For
accurate measurem ents, both the + and – inputs m ust always be
AP034-OM-E Rev D ISSUED: January 2000 ²
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connected to the test circuit. The ground connection is optional.
Positive voltages applied to the + input relative to the – input will
deflect the oscilloscope trace toward the top of the screen.
To maintain the high performance capability of the probe in
measurement applic ations, user care in connecting the probe to
the test circuit. Increasing the parasitic capacitance or inductance
in the input paths may introduce a “ring,” or slow the rise time of
fast signals. To m inimize these effects, use the shortest length
possible when connecting the probe to the circuit under test.
Input leads that form a large loop area (even shielded coaxial
cables) will pick up any radiated magnetic field that passes
through the loop, and may induce noise in the probe inputs.
Because this signal will appear as a diffe rential mode signal, the
probe’s common mode rejection will not remove it. You can
greatly reduce this effect by using short interconnection leads,
and twisting them together to minimize the loop area.
High common mode rejection requires precise matching of the
relative gain or attenuation in the + and – input signal paths.
Mismatches in additional parasitic capacitance, inductance,
delay, and a source impedance differ ence between the + and –
signal paths will lower the common mode rejection ratio.
Therefore, it is desirable to us e the sam e length and type of wire
and connectors for both input connections . W hen possible, try to
connect the inputs to points in the circuit with approxim ately the
same source impedance.
If AC coupling is desired, install the AC coupling accessory on
the probe tip before connecting it to the test circuit. The low-
frequency cutoff (–3 dB point) of the AC coupler is approxim ately
16 Hz.
If the voltage in the test circuit exceeds the probe’s capability,
add the external ÷10 or ÷20 attenuator* to the probe tip. If both
the external attenuator and AC coupler are used, install the
attenuator on the probe tip first, then install the AC coupler on the
attenuator input.
* Note
The external attenuators are precisely adjusted
during manufacturing to match the
² ISSUED: January 2000 AP034-OM-E Rev D
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characteristics of the input of the probe with
which they were shipped. The input
characteristics of the external attenuator itself do
not exactly match those of the probe. Therefore,
using the ÷10 and ÷20 attenuators at the same
time is not recommended. The scale factor
encoding system will not operate correctly with
both attenuators installed simultaneously.
The input characteristics of the AP034 1 GHz
Active Differential Probe are significantly
different than those of the AP033 500 MHz
Active Differential Probe. The external
attenuators are not interchangeable. The
external attenuators currently supplied with the
probes are labeled with the appropriate model
number. The attenuators supplied with model
AP033 probes prior to the introduction of the
AP034 did not include the model number on the
label. When using an external attenuator with the
AP034 Active Differential Probe, make sure it is
labeled “AP034.”
Interchanging non-compatible attenuators will
not damage the probes; however, the transient
response of the measured signals will be
significantly in error.
In addition to being compatible with the included lead set, the
probe input connectors will mate with standard 0.025 in.
(0.635 mm) square pins in any rotational orientation. To avoid
damaging the input connectors, do not attempt to insert
connectors or wire larger than 0.036 in. (0.91 m m) in diameter.
Avoid rotating square pins after they are inserted into the input
connectors.
The included accessories simplify the task of connecting the
probe to the test circuit:
• Use the small (0.5 mm) mini clips with the flexible
lead set when connecting to fine-pitch surface mount
IC leads.
AP034-OM-E Rev D ISSUED: January 2000 ²
PROBE INPUT LOADING
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• The larger (0.8 mm) mini clips can be used to
connect to through-hole leaded components.
• The offset round pins can be used for hand-held
probing applications. Reposition the pins by rotating
them to obtain the required spacing.
Attaching any probe to a test circuit will add some loading. In
most applications, the high impedance of the AP034 Active
Differential Probe inputs im parts an insignificant load to the test
circuit. However at very high frequencies, the capacitive
reactance of the probe’s input capacitance may load the circuit
enough to affect meas urement accuracy. The equivalent model
of the probe input circuits is shown below:
GROUNDING THE PROBE
+
≈ 0.1 pF
1.5 pF
1 MΩ
Figure 1. AP034 Equivalent Input Model
The single lead along with one of the larger (0.8 mm) m ini clips
can be used to ground the probe to the test circuit. Insert the pin
end of the lead into the receptacle marked:
Note
Do not use the attenuator encoding receptacle
(unmarked socket near the – input) to ground the
probe. Connecting to the encoding receptacle
will not provide adequate grounding, and may
result in in correct scale factor indication.
-
1.5 pF
1 MΩ
² ISSUED: January 2000 AP034-OM-E Rev D
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