DA
1855A
Leading
Features
-
100ns
Overdrive Recovery
-
DC
to 100 MHz Bandwidth
-
100,000
to 1 CMRR
-
Gain
1 or 10
-
Very
Low Noise
The
DA1855A is a stand-alone, high-performance 100 MHz
differential amplifier. It is intended to act as a signal
conditioning preamplifier for oscilloscopes, digitizers and
spectrum analyzers, providing differential measurement
capability to instruments having only a single-ended input.
When used with a DA1855A, oscilloscopes can
obtain Common Mode Rejection Ratio (CMRR) and overdrive
recovery performance levels previously unobtainable.
Amplifier
gain can be set to 1 or 10. A built-in input attenuator can be
separately set to attenuate signals by a factor of 10,
providing gains of 10, 1, or 0.1 and common mode dynamic range
of �15.5 V (�1) or �155 V (�10). Optional probes increase
the maximum input signal and common mode ranges in proportion
to their attenuation ratio but do not exceed their maximum
input voltage rating. Effective gain of the DA1855A, including
probe attenuation, amplifier gain and attenuator settings, is
automatically displayed.
The
DA1855A has a bandwidth of 100 MHz, but any one of the three
3-pole bandwidth limit filters can be selected to reduce
bandwidth to
20 MHz, 1 MHz or 100 kHz to limit noise above the frequency of
interest.
The
DA1855A output is carefully limited to �500 mV, so that the
oscilloscope is not overdriven by large inputs. This allows
many oscilloscopes to directly measure the settling of D/A
converters with 14-bit (60 ppm) precision, better than any
other differential comparator.
The
DA1855A features a built-in Precision Voltage Generator (PVG)
that can be set to any voltage between �15.5 volts (�10
volts in Differential Offset) with up to 100 킮 resolution. The PVG's output can be selected as an input to the
inverting (-) input of the amplifier for operation as a
differential comparator or applied internally as a true
differential offset voltage. The PVG is also available for
external use through a rear panel connector.
The
DA1855A operates from 90 to 250 VAC line without line
switching.
High-performance
differential probes such as the DXC100 �10/�100 high CMRR
probes are recommended.
Overdrive Recovery
With
a �100 probe, the DA1855 settles to within 100 mV referred to
input, from a 400 V input signal within 100 ns. With
attenuating probes, this allows the in circuit measurement of
dynamic saturation in switch mode power converter switching
devices.
Comparator
Mode
The
DA1855A becomes a differential comparator when the internal
Precision Voltage Generator (PVG) output is selected as the
amplifier's inverting (-) input. In this mode, the DA1855A can
be used to very accurately measure relatively small signals
that are riding on large AC or DC components. Due to the
precision of the voltage generator, an oscilloscope, when used
with the DA1855A, can make voltage measurements that are much
more accurate than the oscilloscope is capable of by itself.
The output of the PVG is available for external use via a rear
panel connector.
True
Differential Offset Mode
The
DA1855A has built-in Precision Voltage Generator can be used
to generate a true differential offset while still allowing
both inputs to be used as differential inputs. The offset
range can be as high as �50,000 divisions and the generator
has 5 1/2 digit resolution. This mode
facilitates making measurements such as changes to a
transistor's base to emitter voltage caused by variations in
temperature and/or current. Used in this mode, the voltage
generator can be set to a value that will zero out the static
value of the junction's on voltage. The DA1855A's differential
measurement capability will reject any dynamic signal common
to both sides of the junction, and the oscilloscope is left to
measure only the changes in the junction voltage.
Autobalance
Each
time either gain setting button is pressed, the DA1855A
automatically adjusts the amplifier's DC Balance.
Specifications
| Nominal |
| Amplifier
gain: |
x1
or x10 |
| Output
impedance: |
50
ohm |
| Intended
output load: |
50
ohm |
| Maximum
output: |
limited
at �0.50 V into 50 ohm. |
| Input
attenuation: |
�1
or �10 |
| |
| Overdrive
Recovery (Typical): |
In
X10 gain, amplifier settles within 1 mV
referred to the input within 100 nsec from 4 V
input.
(8000% overdrive) |
|
|
| Input
Resistance: |
| (�1
Attenuator, x1 or x10 GAIN): |
1
MΩ or 100 MΩ |
| (�10
Attenuator, x1 or x10 GAIN): |
1
MΩ |
Input
capacitance
(�1 or �10): |
20
pF |
| Bandwidth
limit filters: |
20
MHz,1.0 MHz and 100 kHz |
| Filter
characteristics: |
18
dB/octave (3-pole Bessel) |
| +
Input selections: |
AC,
OFF (precharge), DC |
| -
Input selections: |
AC,
OFF (precharge), DC, Vcomp |
| Input
coupling capacitor: |
0.1
킚, 400 V DC |
| Input
protection: |
protected
to �250 V, automatic input disconnect with manual
reset. |
| |
|
|
Differential offset accuracy: |
| (Typical) |
|
| (x10
GAIN, �1 Attenuator): |
0.1%
+ 50 킮2 |
| (x1
GAIN,�1 Attenuator): |
0.1%
+ 500 킮2 |
| (x10
GAIN, �10 Attenuator): |
0.15%
+ 500 킮2 |
| (x1
GAIN, �10 Attenuator): |
0.15%
+ 5 mV2 |
| |
|
| Warranted Characteristics |
| Gain
accuracy: |
�1%
+ uncertainty of termination resistance |
| Output
Zero: |
≤2
mV referred to input |
| Bandwidth: |
>100
MHz (X1 gain, -3dB) |
| Risetime: |
<3.5
ns (calculated from bandwidth) |
| Common
mode rejection ratio, X1 or X10 Gain, �1
Attenuation: |
|
≥
50,000:1 (94 dB) @ 70 Hz
≥ 50,000:1 (94 dB) @ 100 kHz
≥ 316:1 (50 dB) @ 10 MHz |
| |
|
| Dynamic
Ranges |
| Max
differential linear input: |
500
mV
|
x
(combined internal and probe's attenuation
factor) |
| Gain
Setting |
|
| (x10
GAIN, �1 Attenuator): |
�50mV
or �0.5 V with �10 probe |
| (x1
GAIN, �1 Attenuator): |
�0.5V
or �5.0 V with �10 probe |
| (x10
GAIN, �10 Attenuator): |
�0.5V
or �5.0 V with �10 probe |
| (x1
GAIN, �10 Attenuator): |
�5.0V
or �50 V with �10 probe |
| |
|
| Maximum
input slew rate: |
| (�1
Attenuator, �1 probe): |
0.15
V/�s |
| (�10
Attenuator or �10 probe): |
1.5
V/�s |
| (�10
Attenuator and �10 probe): |
15
V/�s |
| (�1
Attenuator and �100 probe): |
15
V/�s |
| (�10
Attenuator and �100 probe): |
150
V/�s |
| |
|
| Max
Common Mode Range: |
| (�1
Attenuator): |
�15.5
V (x1 or x10 GAIN) |
| (�10
Attenuator): |
�155
V (x1 or x10 GAIN) |
| (�10
Attenuator and x10 probe): |
�1.55
kV (x1 or x10 GAIN) |
| |
|
| Differential
Offset Range (VDIFF mode referred to
input) |
| (x10
GAIN, �1 Attenuator): |
�1
V |
| (x1
GAIN, �1 Attenuator): |
�10
V |
| (x10
GAIN, �10 Attenuator): |
�10
V |
| (x1
GAIN, �10 Attenuator): |
�100
V |
| (x1
GAIN, �10 Attenuator, x10 probe): |
�1.0
kV |
|
|
| Comparison
Offset Range (Vcomp mode, referred to
input): |
| (�1
Attenuator): |
�15.5
V (x1 or x10 GAIN) |
| (�10
Attenuator): |
�155
V (x1 or x10 GAIN) |
| (x10
probe and �10 Attenuator): |
1.55
kV (x1 or x10 GAIN) |
| |
|
| Precision
Voltage Source |
| Output
range: |
�15.5
V |
| DC
accuracy: |
0.05%
of reading +500 킮 (15� to 45캜) |
| Control: |
Oscilloscope
offset knob |
| |
|
| Power
Requirements |
| Line
voltage requirement: |
90
to 250 V AC |
| Line
frequency range: |
45
- 66 Hz |
| Power
Consumption: |
~28
W, ~ 39 VA |
|
|
| Environmental
Characteristics |
| Operating
Range: |
0�
to 50캜 |
| Non-Operating: |
-4�
to 75캜 |
| |
|
| Physical
Characteristics |
| Height: |
7.29
cm (2.87") |
| Width: |
21.2
cm (8.36") |
| Depth: |
23.2
cm (9.12") |
| Weight: |
2.15
kg (4.75 lb) |
| Shipping
Weight: |
3.12
kg (6.88 lb) |
| |
|
| Warranty: |
3
years |
|
|
|
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