The
AP033 is a high-performance active differential probe.
High bandwidth, excellent common mode rejection ratio
(CMRR) and low-noise floor make the AP033 ideal for
applications such as disk drive design and failure
analysis as well as wireless and data communication
design.
Fully
Integrated: With the ProBusTM
interface, the AP033 becomes an integral part of the
oscilloscope. The probe sensitivity and offset can
be controlled from the oscilloscope front panel, the
probe front panel, or by using remote control commands
(GPIB or RS-232). Sensitivity, offset, input capacitance,
and common mode voltage range are displayed on the
oscilloscope screen. When used with a LeCroy digital
oscilloscope, no external power supply is required.
Wide
Dynamic Range: The AP033 provides a range
of sensitivities from x10 gain to ÷10 attenuation
(even ÷100 with plug-on attenuator) for diverse signals.
The sensitivity can be adjusted continuously from
200 µV/div to 1 V/div, when used with a LeCroy oscilloscope.
At
high sensitivities, the x10 GAIN and the ÷1 ATTENUATION
are selected. This produces input noise, ±5 V of common
mode voltage range (CMVR), and ±400 mV of DC differential
offset. At lower sensitivities, the x1 GAIN and ÷10
ATTENUATION are selected, resulting in ±50 V CMVR
and ±4 V of differential offset.
The
input capacitance is just 2 pF/side (1 pF differential)
whenever the ÷10 ATTENUATION is selected. Deflection
factors of 2 mV/div to 1 V/div can be obtained with
only 2 pF/side input capacitance and ±50 V CMVR.
DC
CMRR is greater than 10,000:1 (80 dB) in both ATTENUATION
settings.
OFFSET
up/down buttons allow OFFSET control from the probe
amplifier body. Momentarily holding both buttons will
zero the OFFSET.
A
supplied AC coupling capacitor head (0.1 µF) allows
operation with large common mode or differential DC
inputs.
The
input attenuator automatically changes from ÷1 to
÷10 when too much common mode signal is sensed. This
and a fast input protection circuit also serve to
protect the input from potentially damaging signals.
When the probe is removed from the oscilloscope or
the power is turned off, the ÷10 ATTENUATION is automatically
invoked, leaving the inputs protected when not in
use.
Gain
and Attenuation Selections
The
AP033 consists of a probe head with ÷1 or ÷10 attenuation
and an amplifier body which attaches to the scope
front panel. The amplifier gain can be either x1 and
x10. Both the probe head attenuator and amplifier
gain are controlled through the ProBus interface.
Normally the GAIN and ATTENUATION selections are accomplished
by the oscilloscope as shown in the table below.
There
are two ways of obtaining x1 gain from the AP033:
x1 GAIN with ÷1 ATTENUATION, or x10 GAIN with ÷10
ATTENUATION. The oscilloscope selects the latter of
these two options (as shown below) to provide minimum
input capacitance and maximum common-mode dynamic
range while still leaving low noise operation available
at the highest sensitivity.
By
using the probe amplifier body control to override
the automatic selection, the x1 GAIN with ÷1 ATTENUATION
option is readily available for 10 mV, 20 mV and 50
mV/div. CMVR is ±5 V, input capacitance is 5 pF, and
noise is . Similarly, x10 GAIN and ÷10 ATTENUATION
can be selected at 2 mV/div and 5 mV/div for 2 pF
input C and ±50 V CMVR. The oscilloscope displays
the correct deflection factor in all cases.
Using
the supplied accessory plug-on attenuator head, gain
selections from 100 mV/div to 10 V/div are available.
Input
Characteristics
The
input capacitance is modeled by 2 pF to ground from
each input plus 0.20 pF from input to input when the
÷10 ATTENUATION is selected. This is equivalent to
1.20 pF differential input capacitance. With ÷1 ATTENUATION,
the differential input capacitance is 2.7 pF.
Input
resistance is 1 Mohm at all GAIN and ATTENUATOR settings,
including the accessory plug-on attenuator head.
An
AC coupling plug-on accessory features a 0.1 µF coupling
capacitor for each input. The low-frequency CMRR is
reduced.
Autobalance
Holding
both offset buttons down for two seconds with the
input connections removed invokes Autobalance. This
provides the highest accuracy on all ranges by removing
residual DC offset from the probe.
Low
Noise
At
full gain, the noise is less than 4 nV/ˆHz, the
lowest of any available differential probe.
Common
Mode Sensing and Input Protection
It
is not uncommon for a differential amplifier to be
connected to a signal whose common- mode voltage exceeds
the amplifier's common-mode range. Faulty readings,
including total loss of signal, can result. The AP033
senses when signals exceed ±5.5 V and switches its
input attenuator into the signal path. The oscilloscope
shows the new deflection factor, and the probe continues
to work.
The
same mechanism protects the probe from damage due
to large input signals. The probe amplifier is protected
from large, fast-rising signals until the input attenuator
can provide permanent protection. This takes about
1 ms. With the input attenuator in place, the input
can withstand 200 V DC indefinitely.
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