Preamble Instruments 1820, 1822, 1820-PR2, 1822-PR2 Operator's Manual
-,~ ~OREAMBLE
-
VIINSTRUMENTS
1820/1822
DIFFERENTIAL AMPLIFIER
OPERA TOR’S
MANUAL
Revision D
August 1999
Table of Contents
Section 1
Specifications
Introduction .............................................................................
1 - 1
1820/1822 Specifications ........................................................
1-2
Nominal Characteristics ..........................................................
1-3
Warranted and Typical Characteristics .................................... 1-4
Environmental and Physical Characteristics ............................
1-5
Section 2
Operating Instructions, Controls and Indicators
Front Panel ..............................................................................
2-1
Rear Panel ...............................................................................
2-4
Oscilloscope Settings ...............................................................
2-5
Model 1820 Operation .............................................................
2-6
Section 3
General Operating Information
Getting Started .........................................................................
3-1
1822 Front Panel Operation .....................................................
3-1
Comparison Voltage Operation ...............................................
3-2
Differential Offset Operation ..................................................
3-3
User Traps to Avoid ................................................................
3-4
Section 4
Performance Verification
Introduction ............................................................................. 4-1
Test Equipment Required ........................................................
4-2
Preliminary Procedure .............................................................
4-3
Procedure .................................................................................
4-3
1820/1822 Test Record ..........................................................
4-11
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Section 1
Specifications
Introduction
182011822 Operator’s Manual
The 1820 and 1822 are stand-alone high performance
100 MHz differential amplifiers. They are intended to act
as signal conditioning preamplifiers for oscilloscopes,
digitizers and spectrum analyzers, providing differential
measurement capability to instruments having only a
single-ended input.
The high gain of the 1820/1822 can extend the sensitivity
of an oscilloscope with 1 mV/div to 1 laV/div. A built-in
input attenuator may be separately set to attenuate signals
by a factor of 10, allowing gains of 1000, 100, 10, 1, or
0.1 and common mode dynamic range of +15.5 V (+1)
+155 V (+10). Optional probes further increase the
maximum input signal and common mode ranges in
proportion to their attenuation ratio, but not exceeding the
probe maximum input voltage rating. Effective gain of
the 1822, including probe attenuation, amplifier gain and
attenuator settings, is automatically displayed.
The 1820/1822 has a bandwidth of DC to 10 MHz, but
the operator can select from a full complement of high
and low frequency -3dB points. In critical measurements,
the signal-to-noise ratio can be greatly improved by
restricting the 1820/1822’s bandwidth to the frequency
range of interest.
The 1822 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 5 1/2 digit
resolution. Each digit of the voltage generator output can
be individually incremented or decremented. Positive or
negative polarity can be selected. The PVG 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 voltage is also available to be used externally
through a rear panel connector. In the 1820, this
connector becomes an input through which the user can
apply an external voltage to achieve the same differential
offset and comparator functions.
The 1820/1822 operates from 100 to 250 VAC line
without line switching.
A wide range of high performance differential probes are
available from Preamble Instruments for use with the
1820/1822. These include the +1 XC200 low capacitance
probe, XCI00 selectable (+10/+100) attenuation probe,
and the XC350 +100 high impedance (92 M~ / 2.6 pF)
probe. Differential probes with higher voltage ratings are
also available from Preamble Instruments.
1-1
1820/1822 Operator’s Manual
1820/1822 Specifications
Except where otherwise noted, the following specifications apply to model 1820, 1822,
1820-PR2 and 1822-PR2
Differential Amplifiers.
The specifications are valid for instruments when the following conditions have been met:
The instrument is being operated from a power source which meets the line voltage and frequency specifications.
The instrument has been operating for at least 30 minutes in an environment which is within the operating
environmental specifications.
¯
The instrument has been calibrated within the last 12 months. Calibration was performed in a controlled environment
of 25 +5°C.
Nominal Characteristics
Nominal characteristics describe parameters and attributes which have are guaranteed by design, but do not have
associated tolerances.
General
Input Configuration:
True Differential, + and - Inputs.
Precision Voltage Generator (1822 and 1822-PR2
models), or external offset reference source (1820
and 1820-PR2 models) can be selected as - input
source in VCOMP mode.
Offset Capability
The Precision Voltage Generator (1822 and 1822PR2 models), or external offset reference source
(1820 and 1820-PR2 models) can be used
provide true differential offset.
+ Input Coupling Selections
- Input Coupling Selections
Input Connectors
AC, Off (Precharge),
AC, Off (Precharge), DC, VcouP
BNC. + Input incorporates Probe Attenuation
Coding sensing connector (1822 Only).
Maximum Non-Destruct Input Voltage
Withstands up to +250 V.
Automatic input disconnect with manual reset
Output Configuration
Output Impedance
Intended Output Load
Output Connector
Amplifier Gain
Input Attenuation
Bandwidth Limit Filters (Upper Limit)
Single Ended, Ground referenced.
50
50f)
BNC
X1, X10, XI00, or X1000
+1 or +10
100 Hz, 300 Hz, 1 KHz, 3 KHz, 10 KHz,
30 KHz, 100 KHz, 300 KHz, 1 MHz, 3 MHz
Bandwidth Limit Filters (Lower Limit)
Bandwidth Limit Filter Characteristics
Autobalance
0.1 Hz, 1 Hz, 10 Hz, 100 Hz, 1 KHz, 10 KHz
Single pole, 6 dB/octave
Amplifier initiates an automatic balance cycle
when either gain button is depressed.
Effective Gain Indicator
(1822 and 1822-PR2 models only)
LEDs indicate the effective gain by factoring
Probe Attenuation, Attenuator and Gain settings.
(Probes must have coding connectors.
+ 1, + 10, + 100, and + 1000 probes are
recognized.)
1-2
182011822 Operator’s Manual
Nominal Characteristics (continued)
Dynamic Ranges
Maximum Differential Linear Input:
X 1000 Gain, + 1 Attenuator
X100 Gain, +1 Attenuator
X 10 Gain, - 1 Attenuator
XI Gain, +l Attenuator
XI000 Gain, +10 Attenuator
X 100 Gain, + I 0 Attenuator
X 10 Gain, + ! 0 Attenuator
XI Gain, +10 Attenuator
~
+5 mV
j
+50 mV
1
+0.5 V
I
+5 V
I
_+50 mV
l
¯ +0.5 V
~
+5 V
t
+50 V
Maximum Common Mode Input
+ 1 Attenuator
+ 10 Attenuator
1
+15.5 V
l
¯ +155 V
Differential Offset Range (VD~FV Mode)
(referred to input)
X 10, X 100, X 1000 Gain, + 1 Attenuator
X 1 Gain, + ! Attenuator
Xi0, X100, XI000 Gain, +10 Attenuator
X ! Gain, +l 0 Attenuator
I
¯ +! V
1
¯ +!0 V
l
±10 V
I
±100 V
Comparison Offset Range (VcoMP Mode)
(referred to input)
+ 1 Attenuator
+ 10 Attenuator
Output Range
I
_+15.5 V
I
¯ +i55 V
Limitedto _+5 V into 50 ~ load
t Voltages are referred amplifier input connector. Multiply by probe attenuation factor to obtain value refer to probe
input. (e.g. _+50 mV1 becomes +0.5V at the probe tip when using a +10 probe.)
Precision Voltage Generator (1822 and 1822-PR2 models
Output Range
Resolution
Control
Reference Type
Output Routing
Autozero
Power Requirements
Line Voltage Range
Line Frequency Range
only)
±15.5 V
1 O0 p.V
Individual increment and decrement buttons for
each digit. Digit carries over to next decade.
Oven stabilized buried Zener
Can be applied to - input and available at rear
panel BNC connector.
Removes output offset when 0.0000 volts is
selected and periodically thereafter.
100 - 250 VAC
48 - 66 Hz
1-3
1820/1822 Operator’s Manual
Warranted Characteristics
Warranted characteristics describe parameters which have guaranteed performance.
provided in the Performance Verification Procedure for all warranted specifications.
Unless otherwise noted, tests are
Gain Accuracy
+1% + Uncertainty of termination resistance
Bandwidth (- 3dB)
X1 or XI0 Gain
X 100 Gain
X 1000 Gain
Rise Time (XI or X10 Gain)
>10 MHz
>2.5 MHz
>1 MHz
<35 ns (Calculated from Bandwidth)
Common Mode Rejection Ratio
(X 1 or X 10 Gain)
70 Hz
100 KHz
1 MHz
Precision Voltage Generator Accuracy
>100,000:1 (100 dB)
>100,000:1 (100 dB)
>1,000:1 (60 dB)
0.05% of reading + 500 ~tV (15° to 45° C.)
Typical Characteristics
Typical characteristics describe parameters which do not have guaranteed performance. Tests for typical characteristics
are not provided in the Performance Verification Procedure.
Input Resistance
+1 Attenuator
1 MF2 or 100 Mr2
1 Mr2 only with attenuating probe
+ 10 Attenuator
Input Capacitance
AC Input Coupling Capacitance
+ 10 Attenuator Accuracy
DC Drift (X10 Gain, referred to input)
Input Leakage Current
1 Mr2
20 pF
0.1 ~tF
0.05%
50 ~tVPC
<10 pA (0° - 45° C.)
(X 1 or X 10 Gain, + 1 Attenuator)
Differential Offset Accuracy
X i 0, X 100, X 1000 Gain, + 1 Attenuator
XI Gain, +1 Attenuator
X 10, X 100, X 1000 Gain, + 10 Attenuator
XI Gain, +10 Attenuator
Precision Voltage Generator Temperature
O. 1% + 50 laV
2
0.1% + 500 ~tV
2
O. 15% + 500 ~tV
2
O. 15% + 5 mV
<5 mVPC of full scale
2
Coefficient (1822 and 1822-PR2 models)
Power Consumption
26 W, ~ 36 VA (1820 and 1822)
52 W, ~ 72 VA (1820-PR2 and 1822-PR2)
2 Voltages are referred amplifier input connector. Multiply by probe attenuation factor to obtain value refer to probe
input. (e.g. 0.1% + 50 ~tV2 becomes 0.1% + 500 laV at the probe tip when using a +10 probe.)
1820/1822 Operator’s Manual
Environmental Characteristics
The Environmental Characteristics are tested to specification MIL-T28800D Class 5.
performance verification of environmental characteristics is required.
Refer to this specification if
Temperature Range, operating
Temperature Range, non-operating
0° - 50° C.
-40° - 75° C.
Physical Characteristics
Height
Width
Depth
Weight
Shipping Weight
7.29 cm (2.87") (1820 and 1822 models)
8.75 cm (3.4") (1820-PR2 and 1822-PR2 models)
21.2 cm (8.36") (1820 and 1822 models)
43.9 cm (17.3") (1820-PR2 and 1822-PR2 models
without rack mounting ears installed)
23.2 cm (9.12") (1820 and 1822 models)
42.5 cm (16.7")(1820-PR2 and 1822-PR2 models)
2.15 kg (4 Ibs. 12 oz.) (1820 and 1822 models)
9.5 kg (21 lbs.) (1820-PR2 and 1822-PR2 models)
3.12 kg (6 lbs. 14 oz.) (1820 and 1822 models)
11.3 kg (25 lbs.) (I 820-PR2 and 1822-PR2 models)
Compliances
EC Declaration of Conformity
Designed to comply with EN61010-1 : 1993
Installation Category l, 42.2V, pollution degree 1.
Conforms to Low Voltage Directive 73.72 EEC for
product safety.
1-5
1820/1822 Operator’s Manual
Section 2
Operating Instructions, Controls, and Indicators
Front Panel
Attenuator
Signals connected to the +INPUT and the -INPUT are
connected either directly to the 1820/1822’s amplifier
inputs or to the input attenuators. The input attenuators
are passive networks which divide each signal by ten.
In ÷1 mode the front panel input connectors are directly
connected to the 1820/1822 amplifier’s differential inputs.
In ÷10 mode each front panel input connector is
connected to a passive 1 Mr2 attenuator. The attenuator
output is connected to the 1820/1822 amplifier’s
corresponding differential input. The signal at each input
is attenuated by a factor of ten.
Gain
The 1820/1822 amplifier gain (amplification) is selectable
XI, XI0, XI00 and XI000. The amplified signal appears
at the rear panel AMPLIFIER OUTPUT connector.
A signal connected to the +INPUT will maintain its
polarity at the output connector. A signal connected to
the -INPUT will be inverted in polarity.
Proper gain is obtained when the 1820/1822 drives a 50
load such as an oscilloscope with input impedance set to
50 fL An oscilloscope with only 1 Mr2 input impedance
available should have a 50 f2 coaxial termination placed
on its input connector. The ! 820/1822 is then connected
to the oscilloscope through the coaxial termination.
The amplifier gain and the input attenuator are
individually selectable to provide versatility. For
example, the comparison voltage range is changed from
+15.5000 to ±155.000 volts by changing the
ATTENUATOR from +1 to ÷10. The overall gain can
still be set to 100, 10, 1 or 0.1 by selecting the GAIN
mode, XI000, X100, XI0 or XI, as desired.
Autobalance is a feature invoked when any gain button is
pushed, even if a different gain is not selected.
Autobalance momentarily sets the INPUT COUPLING
to OFF and determines the offset necessary to set the
output at 0 volts within about 25~tV. During this process
the front panel input coupling controls are unresponsive.
When finished, the INPUT COUPLING returns to its
previous mode. Autobalance usually takes less than one
second. This handy feature allows the operator to DC
balance the 1820/1822 simply by pushing the GAIN
button which is already illuminated. When changing
gains, the Autobalance feature is automatically invoked,
freshly adjusting the amplifier’s DC balance.
+Input Coupling (AC-OFF-DC)
INPUT COUPLING
CAPACITOR
+ INPUT
CONNECTOR [----11--7 AC ~11 I+1[
0.I~ .......
l [ r--- , ¯
10 900 K~ +10
ATTENUATOR
11111
i
In OFF mode, the input connector is disconnected from
the amplifier input, and the amplifier input is connected to
ground. The AC coupling capacitor is connected between
the +INPUT and ground through 1 M~ (either the input
attenuator or the input resistor), independent of the
INPUT RESISTANCE selected. In this mode, the AC
coupling capacitor is quickly charged to the average DC
input voltage. OFF mode is also referred to as precharge
mode. Precharge is particularly useful when planning to
AC couple and measure voltages in excess of 19 volts.
The 1820/1822 input coupling is set to OFF and
connected to the circuit under test. When the +INPUT is
changed from OFF to AC mode, the coupling capacitor is
already charged, and the trace properly centered on the
oscilloscope screen. Additionally, the risk of tripping the
input overload detector and automatically disconnecting
the input is eliminated.
In the AC mode, the +INPUT is connected through an
AC coupling capacitor to the amplifier input or the input
attenuator. The coupling capacitor retains its charge
when the input is switched to DC, making it possible to
return to the same circuit without the precharge time. But
this also makes it possible to discharge the coupling
capacitor into another circuit under test if its DC voltage
differs by more than approximately 19 volts from the
voltage on the coupling capacitor. Although the
discharge current is limited to about 70mA, this could
damage some circuits. It is therefore recommended that
2-1
182011822 Operator’s Manual
the +INPUT COUPLING first be changed to OFF
(precharge) when measuring a new circuit point. This
will safely recharge the AC coupling capacitor in less
than 0.3 seconds. The value of the AC coupling capacitor
is 0.1 laF.
DC and low frequencies are attenuated by the AC
coupling capacitor and the input resistance. With the
ATTENUATOR set to +10, or set to +1 with the INPUT
RESISTANCE set to 1 Mr2, the low frequency cut off
(-3dB point) is approximately 1.6Hz, lower than most
oscilloscopes by a factor of 5. When the input attenuator
is set to +1, the INPUT RESISTANCE may be set to
100 M~, and the -3dB point is 0.016Hz. This extremely
low frequency cut off is often handy in observing low
frequency noise riding on large (up to 400 volts)
voltages.
In the DC mode, the +INPUT connector is connected to
the amplifier either directly or through the input
attenuator, and the AC and DC attenuation are the same.
-Input Coupling (AC-OFF-DC-VcoMP)
PRECISION
VOLTAGE )-
REFERENCE
INPUT COUPLING
CAPACITOR
- INPUT
CONNECTOR
~ I.~ /-" .........
l r Ac
("~ I1~
I
~ -+lOT 900 KI] ~*10-
/7/ INPUT
FROM
100 II Vcoup
~
I I
H
ATTENUATOR
111.1 KI2
v A_
/ (’O--I
1 I / / I
I
]
M OF L
~______.~..~’~O ). AMPLIFIER
I
ION-
~1 Mr1
RESISTANCE
100 Mfl fl
INPUT
-INPUT
inverting input. The 1820/1822 output is therefore zero
whenever these two voltages are equal. For this reason,
the voltage applied to the inverting input is called a
comparison voltage, VcoMP.
VcoMP is often used to make precise measurements of
large signals by comparing the accurately known Vcome
with the unknown signal. It is also used to measure the
actual voltage at any point ofa waveform.
PVG output range is +15.500 volts. The PVG is never
attenuated by the input attenuator. Attenuation of the
+INPUT signal by the -10 input attenuator will cause the
PVG to null out an input voltage up to ±155.00 volts
which is ten times larger than the actual PVG voltage.
When the 1822 is used with attenuating probes that
feature readout, the PVG display is changed to indicate
the voltage at the +INPUT probe tip which will bring the
amplifier output to zero.
The -INPUT connector is not useable when Vcome is
selected.
VDIFF (differential offset voltage) is an instrument mode
rather than a type of input coupling. The VBIFF mode
allows the PVG (or an external source in the 1820)
inject an offset signal into the 1820/1822 while still using
both inputs for full differential operation. This mode can
be used as a position control to move the trace on the
oscilloscope screen in preference to using the
oscilloscope’s position or offset control. The
oscilloscope’s position and offset controls should always
be set to zero so that the 1820/1822’s dynamic range is
properly centered. Operation of the 1820/1822 using the
VD|FF function is the same as VCOMP except for the
following:
The -input has the same coupling modes as the +input
plus one additional option, VcoMv (comparison voltage).
The 1822 generates a voltage controlled by the push
buttons above and below the front panel numerical
display. This voltage is called the Precision Voltage
Generator (PVG).
In VCOMP mode, the 1822’s PVG is connected to the
amplifier’s inverting input through an internal filter
designed to eliminate radio and television signal
interference. The 1820 does not have the PVG, but uses
an externally supplied voltage. See Page 2-6 for VcoMv
operation with the 1820.
The 1820/i 822’s amplifier subtracts the voltage applied to
its inverting input from the voltage applied to its non-
¯
The -INPUT remains active, allowing full use of the
1820/1822 as a differential amplifier.
The maximum range of the PVG (1822) or the
external source (1820) is ±10.000 volts in XI Gain
and ±1.0000 volts in X10 to 1000X gain settings.
The effects of the +10 input attenuator and probe
attenuation are the same as when using VCOMP, i.e.
any input attenuation multiplies the effective offset.
The 1822’s PVG display is changed to indicate the voltage
that, if applied between the +INPUT and -INPUT, would
bring the amplifier output to zero. When the 1822 is used
with attenuating probes that feature readout, the PVG
display is scaled to include the effect of probe attenuation.
2-2
1820/1822 Operator’s Manual
Input Resistance
When the input ATTENUATOR is set to -1 and no
attenuating probe is connected, the input resistance can be
increased from 1 Mr2 to 100 Mr2 by pressing the
100M/IM button. This is advantageous when measuring
high impedance circuits or when AC coupling is needed
with a very low frequency cut off. When the input
ATTENUATOR is set to -10 or an attenuating probe
with readout capability is attached, 1 Mr2 (IM) input
resistance is automatically selected.
Unbalanced source impedances can have an adverse
effect on common mode rejection. For example, a
differential source with impedances of 1000 and 2000 [2,
each loaded with 1 M£2 will have a common mode
rejection ratio (CMRR) of 1000 to 1. The common mode
rejection ration can be improved to 100,000 to 1 by using
100 M~ input resistance.
This limitation is also apparent when trying to make
accurate measurements using VCOMP. A 10.000 volt
reference with a 1000 f2 output impedance will be
reduced to 9.9900 volts by the 1820/1822 1 M~ input
resistance, introducing a 10 mV error in the measurement.
Increasing the input resistance to 100 M~ decreases this
error to 100~tV.
frequency -3 dB points are 3MHz, I MHz, 300kHz,
100kHz, 30kHz, 10kHz, 3kHz, IkHz, 300Hz and 100Hz.
Selections for the lower -3 dB points are 0.1Hz, IHz,
10Hz, 100Hz, lkHz and 10kHz. These filters make it
possible to improve the signal-to-noise ratio when making
measurements on microvolt magnitude signals.
Precision Voltage Generator (1822 Only)
The PVG generates the voltage which is used in the
VCOMP and VDWF modes and appears at the rear panel
PRECISION VOLTAGE GENERATOR OUTPUT
connector.
Above each digit is a push button which increments the
corresponding digit by one when pushed. When held, the
digit continues to increment, eventually incrementing the
next higher digit.
Similarly, below each digit is a push button which
decrements the corresponding digit.
The 4- button above the left-most digit changes the PVG
output polarity. The ZERO button below the left-most
digit sets the output to zero and invokes the Autozero
function.
Oscilloscope inputs have a small input current which can
cause an offset when measuring high impedance circuits.
The offset can be observed by opening and shorting the
input to ground. The 1820/1822 has a temperaturecompensated input current pull away (cancellation) which
works in both the 1 M~ and 100 Mr2 INPUT
RESISTANCE modes. Its input offset current is
considerably less than that of most oscilloscopes.
Effective Gain (1822 Only)
Seven lights (LEDs) across the top of the 1822 front panel
indicate the total gain from the instrument input to output.
When the X1 light is lighted, the overall amplifier voltage
gain (amplification) is unity. Similarly, XI0 indicates
overall amplification of ten times. +10 indicates the
voltage amplification is 0.1, and so forth.
When Preamble Instruments or other encoded probes are
properly used, the effective gain includes the probe’s
attenuation factor.
Upper and Lower -3 dB Points
The 1820/22 allows the user to select both the upper and
lower frequency -3 dB points. Selections for the high
Autozero resets the PVG output to zero to eliminate any
drift which may have occurred in the PVG due to low
frequency noise, or long term drift. Autozero is invoked
each time the ZERO button is pressed and re-invoked
approximately every minute thereafter. This is useful
when the instrument has been unplugged and a cold start
is required.
Overdrive (yellow)
When a signal is applied to either input of the 1820/1822
that exceeds its ±15.5 volt input range the yellow
OVERDRIVE indicator is lighted. The light remains on
as long as the input remains larger than the linear range.
The linear range is multiplied by the ATTENUATOR
factor and by the use of an attenuating probe.
The yellow OVERDRIVE light is intended to warn the
user of potentially distorted waveforms.
Overload (red)
When a signal which could damage to the 1820/1822 has
been applied to either input connector, the 1820/1822
protects itself by disconnecting the signal. The input
2-3
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