Stanford Research Systems SIM983 Operation And Service Manual
Operation and Service Manual
Stanford Research Systems
Scaling Amplifier
SIM983
Revision 2.2 • August 28, 2006
Certification
Stanford Research Systems certifies that this product met its published specifications at the time
of shipment.
Warranty
This Stanford Research Systems product is warranted against defects in materials and workmanship for a period of one (1) year from the date of shipment.
Service
For warranty service or repair, this product must be returned to a Stanford Research Systems
authorized service facility. Contact Stanford Research Systems or an authorized representative
before returning this product for repair.
Information in this document is subject to change without notice.
Copyrightc Stanford Research Systems, Inc., 2005, 2006. All rights reserved.
Stanford Research Systems, Inc.
1290–D Reamwood Avenue
Sunnyvale, CA 94089 USA
Phone: (408) 744-9040 • Fax: (408) 744-9049
www.thinkSRS.com • e-mail: info@thinkSRS.com
Printed in U.S.A. Document number 9-01598-903
SIM983 Scaling Amplifier
Contents
General Information iii
Safety and Preparation for Use . . . . . . . . . . . . . . . . iii
Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . vi
1 Getting Started 1 – 1
1.1 Introduction to the Instrument . . . . . . . . . . . . . 1 – 2
1.2 Front-Panel Operation . . . . . . . . . . . . . . . . . . 1 – 3
1.3 Connections . . . . . . . . . . . . . . . . . . . . . . . . 1 – 5
1.4 Power-On . . . . . . . . . . . . . . . . . . . . . . . . . 1 –6
1.5 Restoring the Default Configuration . . . . . . . . . . 1 – 6
1.6 SIM Interface . . . . . . . . . . . . . . . . . . . . . . . . 1 – 7
2 Description of Operation 2 – 1
2.1 Signal Connections and Grounding . . . . . . . . . . . 2 – 2
2.2 Autocalibration . . . . . . . . . . . . . . . . . . . . . . 2– 2
2.3 AC Characteristics . . . . . . . . . . . . . . . . . . . . 2 – 3
2.4 Clock Stopping . . . . . . . . . . . . . . . . . . . . . . 2 – 4
3 Remote Operation 3 – 1
3.1 Index of Common Commands . . . . . . . . . . . . . . 3 – 2
3.2 Alphabetic List of Commands . . . . . . . . . . . . . . 3– 4
3.3 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3– 6
3.4 Commands . . . . . . . . . . . . . . . . . . . . . . . . . 3 – 7
3.5 Status Model . . . . . . . . . . . . . . . . . . . . . . . . 3 – 19
4 Performance Verification 4 – 1
4.1 Verifying the DC Accuracy . . . . . . . . . . . . . . . . 4 – 2
4.2 Verifying AC Performance . . . . . . . . . . . . . . . . 4– 4
4.3 Noise Characteristics . . . . . . . . . . . . . . . . . . . 4 – 6
4.4 Performance Test Record . . . . . . . . . . . . . . . . . 4 – 8
5 Circuit Description 5 – 1
5.1 Circuit Discussion . . . . . . . . . . . . . . . . . . . . . 5 – 2
5.2 Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . 5– 6
5.3 Schematic Diagrams . . . . . . . . . . . . . . . . . . . 5 – 10
i
ii Contents
A Index A – 1
SIM983 Scaling Amplifier
General Information
The SIM983 Scaling Amplifier, part of Stanford Research Systems’
Small Instrumentation Modules family, performs the function
V
= G × (Vin+ V
out
ofs
)
where Vinand V
output of the instrument, respectively, G is a user-specified gain,
and V
within its resolution.
Safety and Preparation for Use
The front-panel input, front-panel output, and the rear-panel output
coaxial (BNC) connectors in the SIM983 are referenced to the Earth,
and their outer casings are grounded. No dangerous voltages are
generated by the module.
CAUTION
Do not exceed ±15 volts to the Earth at the center terminal of each BNC
connector. Do not install substitute parts or perform unauthorized
modifications to this instrument.
The SIM983 is a single-wide module designed to be used inside the
SIM900 Mainframe. Do not turn on the power to the mainframe or
apply voltage input to the module until the module is completely
inserted into the mainframe and locked in place.
are voltages (up to ±10 V) at the input and the
out
is a user-specified offset voltage. The instrument is accurate
ofs
iii
iv General Information
Symbol Description
Alternating current
Caution - risk of electric shock
Frame or chassis terminal
Caution - refer to accompanying documents
Earth (ground) terminal
Battery
Fuse
On (supply)
Off (supply)
Symbols you may Find on SRS Products
SIM983 Scaling Amplifier
General Information v
Notation
The following notation will be used throughout this manual:
WARNING
CAUTION
A warning means that injury or death is possible if the instructions
are not obeyed.
A caution means that damage to the instrument or other equipment
is possible.
Typesetting conventions used in this manual are:
• Front-panel buttons are set as [gain ];
[gain ] is shorthand for “[gain ] & [gain ]”.
• Front-panel indicators are set as OVLD.
• Signal names are set as ¬STATUS.
• Signal levels are set as HIGH.
• Remote command names are set as *IDN?.
• Literal text other than command names is set as OFF.
• Special ASCII characters are set as hCRi.
Remote command examples will all be set in monospaced font. In
these examples, data sent by the host computer to the SIM983 are set
as straight teletype font, while responses received by the host
computer from the SIM983 are set as slanted teletype font.
SIM983 Scaling Amplifier
vi General Information
Specifications
Performance characteristics
Min Typ Max Units
Input Voltage [1] −10.0 +10.0 V
Coupling DC
Resistance 0.99 1.00 1.01 MΩ
Capacitance 26 pF
Bias current [2] 40 pA
Voltage noise [3, 4], 1 kHz 43 nV/√Hz
10 kHz 38 nV/√Hz
Current noise, 10 kHz 3 fA/√Hz
Terminals Grounded BNC [5]
Gain Absolute value 0.01 19.99
Polarity Inverting, non-inverting
Resolution 0.01
Accuracy [2] ±0.01
Stability ±10 ppm/◦C
Offset [3] Voltage
Resolution, |V
| ≤ 1.999 V 1 mV
ofs
|V
| ≥ 2.00 V 10 mV
ofs
−10.00 +10.00 V
Accuracy [2, 4, 6] ±1 ± 200 mV + ppm
Stability [4] ±20 ± 20 (µV + ppm)/◦C
Settling time [7] 2 s
AC −3dB bandwidth, |G| ≤ 1.00 2.0 MHz
performance Gain-bandwidth product, |G| ≥ 1.00 3.0 MHz
[8] |G| ≥ 2.40 5.0 MHz
|G| ≥ 4.20 10.0 MHz
|G| ≥ 9.60 17.0 MHz
Slew rate 70 V/µs
THD, 1 kHz −90 dB
Output Voltage [1] −10.0 +10.0 V
Maximum current ±100 mA
Short circuit duration Indefinite
Resistance 50 Ω
Terminals Grounded BNC, front [5] and rear [9]
Operating Temperature [10] 0 40
◦
C
Power +5, ±15 V DC
Supply current, +5 V 100 mA
±15 V 300 mA
SIM983 Scaling Amplifier
General Information vii
Conditions:
[1] An overload will be detected and the instrument is not guaranteed to
perform properly if these limits are exceeded, or if |Vin+ V
the limits. Continuous application of an input voltage Vinin excess
of ±15 V will damage the instrument.
[2] At 23◦C.
[3] Referred to input.
[4] For |G| ≥ 1. For |G| < 1, the specification applies to the output-referred
noise and offset.
[5] Amphenol 31–10–4052 or similar.
[6] Following an autocalibration at (23±5)◦C within 24 hours; following
a 2-hour warmup.
[7] To within 0.1% of the final value.
[8] The gain-bandwidth product (GBP) determines the −3 dB bandwidth:
For gain G, the bandwidth is GBP/|G|.
[9] Tyco 227169–4 or similar.
[10] Non-condensing.
|exceeds
ofs
General characteristics
Interface Serial (RS–232) through SIM interface
Connectors BNC (2 front [5], 1 rear [9]); DB–15 (male) SIM interface
Weight 1.5 lbs
Dimensions 1.500W × 3.600H × 7.000D
SIM983 Scaling Amplifier
viii General Information
SIM983 Scaling Amplifier
1 Getting Started
In This Chapter
This chapter gives you the necessary information to get started
quickly with your SIM983 Scaling Amplifier.
1.1 Introduction to the Instrument . . . . . . . . . . . . 1 – 2
1.1.1 Front and rear panels . . . . . . . . . . . . . . 1 – 3
1.2 Front-Panel Operation . . . . . . . . . . . . . . . . . 1 – 3
1.2.1 Polarity . . . . . . . . . . . . . . . . . . . . . 1 – 3
1.2.2 Gain . . . . . . . . . . . . . . . . . . . . . . . 1 – 3
1.2.3 Offset . . . . . . . . . . . . . . . . . . . . . . . 1 – 4
1.2.4 Overload . . . . . . . . . . . . . . . . . . . . . 1 – 4
1.3 Connections . . . . . . . . . . . . . . . . . . . . . . . 1 – 5
1.4 Power-On . . . . . . . . . . . . . . . . . . . . . . . . 1 – 6
1.5 Restoring the Default Configuration . . . . . . . . 1 – 6
1.6 SIM Interface . . . . . . . . . . . . . . . . . . . . . . 1 – 7
1.6.1 SIM interface connector . . . . . . . . . . . . 1 – 7
1.6.2 Direct interfacing . . . . . . . . . . . . . . . . 1 – 7
1 – 1
1 – 2 Getting Started
Input BNC
1 kΩ
input protection
1.00 MΩ
High-impedance buffer
Programmable offset
Invert
noninverting
polarity
inverting
polarity
frequency
compensation
Programmable gain
(inverting)
37 Ω
13 Ω
13 Ω
Output BNC,
rear
Output BNC,
front
1.1 Introduction to the Instrument
The SIM983 Scaling Amplifier provides fine adjustable gain and
offset control of an analog signal. The gain (0.01 ≤ |G| ≤ 19.99),
its polarity (inverting or non-inverting), and the offset voltage
(−10.00 V ≤ V
or remotely. A remote computer can access the module through theremote interface
SIM900 Mainframe, using RS–232 or GPIB.
The digital control circuitry in the SIM983 is designed with a special
clock-stopping architecture. The microcontroller is turned on only
when the polarity, gain, or offset are being changed, during remote
communications, or when an overload condition occurs. This guarantees that no digital noise contaminates low-level analog signals.
A user-commanded autocalibration procedure allows one to controlDC accuracy
the input-referred offset to within ±1 mV of the desired value.
The amplifier’s high slew rate allows it to output a ±10 V peak-peak
sine wave at a frequency of 1 MHz. The gain stage of the amplifierAC performance
is compensated in a flexible fashion to provide a sensible pulse response, so the bandwidth of the instrument is adjusted according to
its gain.1The ample output current in the SIM983 permits one to
drive a 50 Ω load.
≤ +10.00 V) can be set from either the front panel
ofs
If the maximum input voltage is exceeded, or the gain or offset cause
the output voltage to exceed its maximum, the appropriate overload
LED turns on. If armed, the module also generates a status signal to
alert the user of the overload condition. The SIM983 can be operated
outside the SIM900 Mainframe by powering it with its required DC
voltages.
A block diagram of the amplifier is shown below in Figure 1.1.
Figure 1.1: The SIM983 block diagram.
1
The gain-bandwidth product changes with the gain.
SIM983 Scaling Amplifier
1.2 Front-Panel Operation 1 – 3
1.1.1 Front and rear panels
1.2 Front-Panel Operation
1.2.1 Polarity
The polarity is the sign of the gain. It is indicated on the upper display
of the front panel. To change the polarity, press the [polarity] button
once. Holding this button has no effect.
Pressing [polarity] has no effect on the input-referred offset. However, a simultaneous press of [polarity] and one of [gain ] has a
special meaning. This press initiates autocalibration (Section 2.2).
1.2.2 Gain
The gain G can be set to an absolute value between 0.01 and 19.99. To
raise or lower the absolute value of the gain, press the button [gain ]
or the button [gain ]. The decimal point position of the gain displayed on the front panel is fixed, so the resolution of the gain is 0.01.
If [gain ] is pressed when the gain G = ±19.99, the press has no effect.
If [gain ] is pressed when G = ±0.01, the press has no effect. Pressing
either [gain ] does not change the polarity.
Figure 1.2: The SIM983 front and rear panels.
SIM983 Scaling Amplifier
1 – 4 Getting Started
If one of [gain ] is pressed and held, the gain is continuously adjusted. The rate of the adjustment increases as the button is held. If
the absolute value of the gain is being lowered, the rate of the adjustment changes as |G| crosses 1.00, and possibly again as |G|crosses 0.10.
If both [gain ] and [gain ] buttons are pressed at the same time, theresetting gain
absolute value of the gain is reset to 1.00. This action does not change
the polarity.
Pressing one of [gain ] and [polarity] at the same time has a special
meaning. This press initiates autocalibration (Section 2.2).
1.2.3 Offset
The input-referred voltage offset V
can be set to a value
ofs
between −10.00 V and +10.00V. Its value, in volts, is shown on
the second line of displays on the front panel of the amplifier.
To increase or decrease the offset, press the button [offset ]
or the button [offset ]. Unlike the gain, the “up” and “down”
buttons adjust the offset, not its absolute value. Thus, for
example, pressing [offset ] when V
V
= −5.48 V. If [offset ] is pressed when V
ofs
press has no effect. If [offset ] is pressed when V
= −5.49 V makes
ofs
= +10.00 V, the
ofs
= −10.00 V, the
ofs
press has no effect.
Between the values −2.00 V < V
< +2.00 V, the offset is selected
ofs
with 0.001 V resolution; the position of the decimal point on the frontpanel displays is shifted to the left. Although the resolution is 0.01 V
for |V
Thus, for example, setting V
| ≥ 2.00 V, the accuracy of the offset is still ±1 mV ± 0.02%.
ofs
= −5.48 V produces V
ofs
= (−5.480
ofs
± 0.001 ± 0.001) = (−5.480 ± 0.002) V.
If one of [offset ] is pressed and held, the offset is continuously
adjusted. The rate of the adjustment increases as the button is held.
If the value crosses the threshold V
= ±2.00 V, the rate changes
ofs
appropriately.
1.2.4 Overload
If both [offset ] and [offset ] buttons are pressed at the same time, theresetting offset
offset is reset to 0.000 V.
There are two overload indicators, one OVLD LED in the INPUT block and one OVLD LED in the OUTPUT block of the front
panel. The overload signal can also be asserted on the ¬STATUS pin.
See Section 3.5.
SIM983 Scaling Amplifier
1.3 Connections 1 – 5
1.2.4.1 Input overload
An overload condition is recognized and the input OVLD LED is
activated if the absolute value of the voltage applied to the input
exceeds certain limits. These limits are typically ±10.0 V, and areoverload limits
between
1.2.4.2 Output overload
1.3 Connections
−10.4 V ≤ V
≤ −9.9 V, 9.9 V ≤ V
min
max
≤ 10.4 V.
The overloaded state is also recognized, and the input overload LED
activated, if the sum of the input voltage and the commanded offset,
|Vin+V
|, exceeds these limits. To distinguish between the two input
ofs
overload possibilities, use the command OVLD?. The overload LED
stays on for a minimum of 50 ms; after this time it turns off if the
overload condition has ceased.
An overload condition is recognized and the output OVLD LED is
activated if the absolute value |G × (Vin+ V
)| exceeds the limits in
ofs
Section 1.2.4.1. The overload LED stays on for a minimum of 50 ms;
after this time it turns off if the overload condition has ceased.
For a discussion of the front and rear BNC connections, see Section 2.1. The SIM interface connector is discussed in Section 1.6.1.
SIM983 Scaling Amplifier
1 – 6 Getting Started
1.4 Power-On
The instrument retains the values of the gain and the offset in nonvolatile memory. Upon power-on, those settings are restored to their
values before the power was turned off.
The power-on configuration of the remote interface is detailed in
Section 3.3.1.
1.5 Restoring the Default Configuration
The default configuration of the SIM983 is G = +1.00, V
= 0.000 V,
ofs
and bandwidth 0 (see Section 2.3.1). This configuration is reached
from the remote interface by issuing the *RST command. To reset
only the gain or the offset to their default values, use button combinations described in Sections 1.2.2 or 1.2.3.
SIM983 Scaling Amplifier
1.6 SIM Interface 1 – 7
1.6 SIM Interface
The primary connection to the SIM983 Scaling Amplifier is the rearpanel DB–15 SIM interface connector. Typically, the SIM983 is mated
to a SIM900 Mainframe via this connection, either through one of the
internal mainframe slots or the remote cable interface.
It is also possible to operate the SIM983 directly, without using the
SIM900 Mainframe. This section provides details on the interface.
1.6.1 SIM interface connector
The DB–15 SIM interface connector carries all the power and communication lines to the instrument. The connector signals are specified
in Table 1.1.
Direction
Pin Signal Src ⇒ Dest Description
1 SIGNAL GND MF ⇒ SIM Ground Reference 1
2 ¬STATUS SIM ⇒ MF Status/service request (GND = asserted, +5 V= idle)
3 RTS MF ⇒ SIM HW handshake (unused in SIM983)
4 CTS SIM ⇒ MF HW handshake (unused in SIM983)
5 ¬REF 10MHZ MF ⇒ SIM 10MHz reference (no connection in SIM983)
6 −5V MF ⇒ SIM Power supply (no connection in SIM983)
7 −15V MF ⇒ SIM Power supply
8 PS RTN MF ⇒ SIM Ground Reference 2
9 CHASSIS GND Chassis ground
10 TXD MF ⇒ SIM Async data (start bit = “0”= +5 V; “1” = GND)
11 RXD SIM ⇒ MF Async data (start bit = “0”= +5 V; “1” = GND)
12 +REF 10MHZ MF ⇒ SIM 10MHz reference (no connection in SIM983)
13 +5V MF ⇒ SIM Power supply
14 +15V MF ⇒ SIM Power supply
15 +24V MF ⇒ SIM Power supply (no connection in SIM983)
1.6.2 Direct interfacing
SIM983 Scaling Amplifier
Table 1.1: SIM interface connector pin assignments, DB–15.
The SIM983 is intended for operation in the SIM900 Mainframe, but
users may wish to directly interface the module to their own systems
without the use of additional hardware.
The mating connector needed is a standard DB–15 receptacle, such
as Tyco part number 747909–2 (or equivalent). Clean, well-regulated
supply voltages of ±15.0 V DC, +5.0 V DC must be provided, following the pinout specified in Table 1.1 and the minimum currents in
the table on Page vi. Ground must be provided on Pins 1 and 8, with
chassis ground on Pin 9. The ¬STATUS signal may be monitored
1 – 8 Getting Started
on Pin 2 for a low-going TTL-compatible output indicating a status
message. See Section 3.5 for the description of status messages.
CAUTION
The SIM983 has no internal protection against reverse polarity, missing
supply, or overvoltage on the +5 V and the ±15 V power-supply pins. Supply voltages above 5.5 V on Pin 13, above +16 V on Pin 14, or below −16 V
on Pin 7 are likely to damage the instrument. SRS recommends using the
SIM983 together with the SIM900 Mainframe for most applications.
1.6.2.1 Direct interface cabling
If the user intends to directly wire the SIM983 independent of the
SIM900 Mainframe, communication is usually possible by directly
connecting the appropriate interface lines from the SIM983 DB–15
plug to the RS–232 serial port of a personal computer.2Connect RXD
from the SIM983 directly to RD on the PC, TXD directly to TD, and
similarly RTS→RTS and CTS→CTS. In other words, a null-modemstyle cable is not needed.
To interface directly to the DB–9 male (DTE) RS–232 port typically
found on contemporary personal computers, a cable must be made
with a female DB–15 socket to mate with the SIM983, and a female
DB–9 socket to mate with the PC’s serial port. Separate leads from
the DB–15 need to go to the power supply, making what is sometimes
know as a “hydra” cable. The pin connections are given in Table 1.2.
DB–15/F to SIM983 Name
DB–9/F
10 ←→3 TxD
11 ←→2 RxD
5 Computer Ground
to Power Supply
7 ←→ −15 V DC
13 ←→ +5 V DC
14 ←→ +15 V DC
1 ←→ Ground 1 (separate wire to Ground)
8 ←→ Ground 2 (separate wire to Ground)
9 ←→ Chassis Ground (separate wire to Ground)
Table 1.2: SIM983 direct interface cable pin assignments.
The distinct Ground References 1 and 2, and the chassis ground, arenote about grounds
not directly connected within the SIM983. Ground 1 carries the return
2
Although the serial interface lines on the DB–15 do not satisfy the minimum
voltage levels of the RS–232 standard, these lines are typically compatible with
desktop personal computers.
SIM983 Scaling Amplifier
1.6 SIM Interface 1 – 9
currents of digital control signals and the power supplies, whereas
the input voltage and the output voltage reference to Ground 2 (Section 2.1.2). When operating in the SIM900, the three grounds are
tied together in the SIM900 Mainframe. Grounds 1 and 2 are connected through back-to-back Schottky diodes, so they cannot be more
than ∼ ±0.35 V apart. The three ground lines should be separately
wired to a single, low-impedance ground source at the power supply.
1.6.2.2 Serial settings
The initial serial port settings at power-on are: baud rate 9600, 8 bits,
no parity, 1 stop bit, and no flow control. The baud rate of the SIM983
cannot be changed. Flow control is not implemented in the SIM983.
The parity may be changed with the PARI command.
SIM983 Scaling Amplifier
1 – 10 Getting Started
SIM983 Scaling Amplifier
2 Description of Operation
This chapter provides a number of additional details of the operation
of the SIM983.
In This Chapter
2.1 Signal Connections and Grounding . . . . . . . . . 2 – 2
2.2 Autocalibration . . . . . . . . . . . . . . . . . . . . . 2 – 2
2.3 AC Characteristics . . . . . . . . . . . . . . . . . . . 2 – 3
2.4 Clock Stopping . . . . . . . . . . . . . . . . . . . . . 2 – 4
2.1.1 Output drive . . . . . . . . . . . . . . . . . . 2 – 2
2.1.2 Grounds . . . . . . . . . . . . . . . . . . . . . 2 – 2
2.3.1 Bandwidth . . . . . . . . . . . . . . . . . . . . 2 – 3
2.3.2 Slew rate . . . . . . . . . . . . . . . . . . . . . 2 – 3
2 – 1
2 – 2 Description of Operation
2.1 Signal Connections and Grounding
2.1.1 Output drive
The output impedance of the SIM983 Scaling Amplifier is 50 Ω.
The amplifier can drive load impedances from ∞ to 50 Ω for the
full ±10 V range of output voltage. When driving a 50 Ω load, the
gain will be half of that displayed on the front panel.
The rear-panel output connector is wired in parallel with the frontpanel output, and shares some of the output impedance (Figure 1.1).
The output stage is not designed to drive two 50 Ω loads simultaneously.
2.1.2 Grounds
Both the input and the output of the SIM983 are referenced to ground.
To maintain the DC accuracy of the instrument, there are two separate ground references. Ground 1 (Pin 1 of the SIM interface connector) provides a return path for digital control signals and the power
supply currents, while Ground 2 (Pin 8 of the interface connector)
serves as the reference point for analog voltages. The outer casings
of the input and the output front-panel BNC connectors are tied to
Ground 2. The output current of the amplifier returns to the power
supply through Ground 2.
2.2 Autocalibration
The outer casing of the rear-panel output BNC is connected to chassis ground, Pin 9 of the DB–15 SIM interface connector. The separate power, analog, and chassis grounds are not directly connected
within the amplifier. When operating in the SIM900 Mainframe, the
three grounds are tied together inside the mainframe, and through
the mainframe to the Earth. Grounds 1 and 2 are connected inside
the SIM983 through back-to-back Schottky diodes, so they cannot be
more than ∼ ±0.35 V apart.
To ensure DC offset accuracy, the amplifier must be self-calibrated
within the 24 hours preceding a measurement. A valid autocalibration must take place at (23 ± 5)◦C with the module warmed up
for at least 2 hours at (23 ± 5)◦C. If the module is being used inside the SIM900 Mainframe, the autocalibration must also be inside
the mainframe. Otherwise, perform the autocalibration with the
same connection to an independent supply as you use for the operation. The autocalibration is only accurate if the output has stabilized
within ±15 mV of zero for at least 2 minutes immediately preceding the calibration. However, the gain and the offset need not be at
SIM983 Scaling Amplifier
2.3 AC Characteristics 2 – 3
their default values; after the calibration completes, these values are
restored.
Disconnect all inputs and outputs to the SIM983 while performing the au-
tocalibration. To calibrate, issue the command ACAL, or press the but-
ton [polarity] and one of [gain ] at the same time. The calibration
completes and the instrument is ready for operation within 2 seconds. If autocalibration is unsuccessful, for example because an
external voltage (which cannot be nulled) is applied to the input, the
calibration parameters revert to their original values and the com-
mand LDDE? will return Code 1.
Autocalibration does not affect gain accuracy.
2.3 AC Characteristics
2.3.1 Bandwidth
The gain-bandwidth product (GBP) of the SIM983 is a measure of
its small-signal behavior, and depends on |G|. Four gain ranges
correspond to four values of gain-bandwidth product, as specified in the table on Page vi. For |G| ≥ 1, the −3 dB small-signal
bandwidth of the amplifier is f
f
−3 dB
(G) & f
(G = 1.00).
−3 dB
= GBP/|G|. For |G| < 1,
−3 dB
2.3.2 Slew rate
The gain-bandwidth product is determined by a compensation capacitor in the feedback path of the gain-stage amplifier. It is possible
to override the value of this capacitor, giving the instrument more
bandwidth. To do this, use the command BWTH. If the bandwidth
is altered in this way, the next front-panel button press will return
the bandwidth to the value appropriate for the current gain. Cycling the power or performing an autocalibration will also return the
bandwidth to its default value for the gain.
If the bandwidth is set to a value other than its default, the amplifier may
exhibit slow settling, excessive ringing, or oscillations.
The small-signal settling time of the amplifier is a complex function
of its gain and its bandwidth.
The slew rate of an amplifier is a measure of its large-signal behavior. It is the maximum rate of change of the output voltage,
measured in V/s. The slew rate (SR) determines the maximum undistorted AC signal that can be output; for a sine-wave output at a frequency f , the maximum peak-peak voltage is |V
max−Vmin
| = SR/(π f ).
The SIM983 is designed to be able to output a full-range sine wave
at 1 MHz.
SIM983 Scaling Amplifier
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