Stanford Research Systems SR446 Operation manual

Operation and Service Manual
400 MHz Programmable Gain Preamplier
SR446
Stanford Research Systems
Revision 1.01 November 18, 2022

ii
Certication
Stanford Research Systems certies that this product met its published specications 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.
Copyright © Stanford Research Systems, Inc., 2022. 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: [email protected]
Printed in the U.S.A. Document Number 9‑01766‑903
SR446 400 MHz Programmable Gain Preamplier

iii
Contents
General Information 1
Safety and Preparation for Use . . . . . . . . . . . . . . . . . . . 2
AC Line Voltage . . . . . . . . . . . . . . . . . . . . . . . . 2
Line Cord . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Symbols on the SR446 . . . . . . . . . . . . . . . . . . . . . . . . 3
Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Specications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Frequency Response . . . . . . . . . . . . . . . . . . . . . . . . . 5
1 Operation 7
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.2 Using the SR446 . . . . . . . . . . . . . . . . . . . . . . . . 9
1.2.1 Input . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.2.2 Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.2.3 Output lter . . . . . . . . . . . . . . . . . . . . . . 10
1.3 Special operations . . . . . . . . . . . . . . . . . . . . . . . 11
1.3.1 Oset calibration . . . . . . . . . . . . . . . . . . . . 11
1.3.2 Factory reset . . . . . . . . . . . . . . . . . . . . . . 11
2 Remote Operation 13
2.1 List of Commands by Subject . . . . . . . . . . . . . . . . . 14
2.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2.1 Interface Conguration . . . . . . . . . . . . . . . . 15
2.2.2 Buers . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3 Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3.1 Command Syntax . . . . . . . . . . . . . . . . . . . 16
2.3.2 Notation . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3.4 Interface Commands . . . . . . . . . . . . . . . . . 17
2.3.5 Input Commands . . . . . . . . . . . . . . . . . . . 18
2.3.6 Gain Commands . . . . . . . . . . . . . . . . . . . . 18
2.3.7 Filter Command . . . . . . . . . . . . . . . . . . . . 19
2.3.8 Utility Commands . . . . . . . . . . . . . . . . . . . 19
2.3.9 Status Commands . . . . . . . . . . . . . . . . . . . 20
3 Performance Verication 21
3.1 Preliminary . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2 DC oset . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3 AC gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
SR446 400 MHz Programmable Gain Preamplier

iv Contents
A Gain Calibration 25
A.1 Preliminary . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
A.2 AC gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
B Circuit Description 29
B.1 Analog board . . . . . . . . . . . . . . . . . . . . . . . . . . 29
B.2 Bridge board . . . . . . . . . . . . . . . . . . . . . . . . . . 29
B.3 Digital board . . . . . . . . . . . . . . . . . . . . . . . . . . 29
B.4 Front panel board . . . . . . . . . . . . . . . . . . . . . . . 30
Schematic Diagrams 31
SR446 400 MHz Programmable Gain Preamplier

1
General Information
Safety and Preparation for Use . . . . . . . . . . . . . . . . . 2
AC Line Voltage . . . . . . . . . . . . . . . . . . . . . . . 2
Line Cord . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Symbols on the SR446 . . . . . . . . . . . . . . . . . . . . . . 3
Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Specications . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Frequency Response . . . . . . . . . . . . . . . . . . . . . . . 5
SR446 400 MHz Programmable Gain Preamplier

2General Information
Safety and Preparation for Use
WARNING
Dangerous voltages, capable of causing injury or death, are present in
this instrument. These voltages can persist for many minutes after AC
power is removed. Do not remove the product covers or panels. Do
not apply power or operate the product without all covers and panels
in place.
AC Line Voltage
The SR446 400 MHz Programmable Gain Preamplier operates from a
90 V–250 V nominal AC power source having a line frequency of 50 Hz
or 60 Hz.
Line Cord
The SR446 400 MHz Programmable Gain Preamplier has a detachable,
three‑wire power cord for connection to the power source and to a
protective ground. The chassis of the instrument is connected to the
outlet ground to protect against electrical shock. Always use an outlet
which has a properly connected protective ground.
Service
The SR446 400 MHz Programmable Gain Preamplier does not have any
user serviceable parts inside. Refer service to a qualied technician.
Do not install substitute parts or perform any unauthorized modications
to this instrument. Contact the factory for instructions on how to return
the instrument for authorized service and adjustment.
SR446 400 MHz Programmable Gain Preamplier

Symbols on the SR446 3
Symbols on the SR446
Warning Risk of electric shock. Injury or death is possible
if the instructions are not obeyed.
Caution Refer to user manual. Damage to the instrument
or other equipment is possible.
Power Toggle instrument power.
Chassis
Ground
Notation
Typeseing conventions used in this manual, with examples of each.
Use case Example
Front‑panel buons [Term]
Front‑panel indicators AC
Remote command names *IDN?
Literal text (sent) *IDN?
Literal text (received) Stanford_Research_Systems,SR446,00000001,3.11.2
SR446 400 MHz Programmable Gain Preamplier

4General Information
Specications
All performance specications after 2 hour warm‑up at (231)C ambient,
and within 24 hours of automatic oset calibration.
Input
Input level 500 mV
AC coup. (3 dB, with 50 source)
50 16 kHz (typ)
500 3 kHz (typ)
Input impedance
50 (50 1) 
500 (500 10) 
Clamp levels 1.5 V
Protection 4 Vdc
Noise (+40 dB, r.t.i.)
1 MHz 3.3 nV/
Hz (typ)
1 Hz to 400 MHz 40 μVrms (typ)
Amplier
Gain 1.0 V/V (0 dB) to 100 V/V (40 dB)
Accuracy 0.5 dB @ 1 MHz
Flatness 0.3 dB, DC to 100 MHz (typ)
Bandwidth (3 dB) 400 MHz (typ)
Gain stability 0.1 %/C (typ)
Oset (r.t.i.) 1 mV
Oset drift 0.8 mV/C (typ)
Outputs
(specied into 50 load)
Source impedance (501) 
Linear operation 0.65 V, each channel
Overload detection 0.8 V (typ)
Limit level 0.9 V
Overload recovery 12 ns (typ)
Rise / Fall time 1 ns (typ)
Propagation delay 4.5 ns (typ)
Dierential skew 20 ps (typ)
General
Inputs 1 (BNC)
Outputs 2 (BNC: inverting and non‑inverting)
Remote interface USB type B
Operating temp. 5C to 40 C, non‑condensing
Mains voltage (85 to 264) Vac, (47 to 63) Hz
Power 15 W (max), 5 W (typ)
Weight 2.3 lb
Dimensions 8.4 1.8 9.1, inches
SR446 400 MHz Programmable Gain Preamplier

Frequency Response 5
Frequency Response
Figure 1 shows the typical frequency response from a 50 source, for
each gain seing from +0 dB (boom curve) to +40 dB (top curve). Some
gain peaking is typical between 200 MHz and 400 MHz.
-8
-6
-4
-2
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
0.01 0.1 1 10 100 1000
Gain, dB
Frequency, MHz
Typical AC Gains vs Frequency
Figure 1: Typical AC gain versus frequency. Measured with AC coupling, 50 
input impedance, and full bandwidth. Input signal generated with 50 source
impedance, amplitude adjusted for 130 mVpp sinusoidal output signal.
SR446 400 MHz Programmable Gain Preamplier

6General Information
SR446 400 MHz Programmable Gain Preamplier

7
1 Operation
This chapter provides an introduction to the SR446 400 MHz Programmable
Gain Preamplier, and a detailed description of its operation from the
front panel.
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.2 Using the SR446 . . . . . . . . . . . . . . . . . . . . . . . 9
1.2.1 Input . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.2.2 Gain . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.2.3 Output lter . . . . . . . . . . . . . . . . . . . . . 10
1.3 Special operations . . . . . . . . . . . . . . . . . . . . . . 11
1.3.1 Oset calibration . . . . . . . . . . . . . . . . . . . 11
1.3.2 Factory reset . . . . . . . . . . . . . . . . . . . . . 11
SR446 400 MHz Programmable Gain Preamplier

81 Operation
1.1 Introduction
The SR446 is a single‑channel, 400 MHz bandwidth voltage preamplier
with 21 programmable gains from 1 to 100 (0 dB to 40 dB) in
2 dB steps. The amplier also includes a programmable low‑pass lter
with four seings: full bandwidth, 200 MHz, 100 MHz, and 20 MHz.
The two 50 outputs provide complementary outputs (inverting and
non‑inverting), and can be used separately or together as a dierential
output.
Stanford Research Systems Model SR446 DC to 400 MHz Programmable Gain Preamplier
Ovld
±500 mV max 50 Ω
AC
Term
–Out +Out Bandwidth Limit
Couple
Units
500 Ω
50 Ω DC
GND 2 dB
steps
dB
V / V
Connect
Error
Standby
full BW
200 MHz
100 MHz
20 MHz
Hold on
GND to null oset
50 Ω
INPUT REMOTE
POWER
INPUT SETUP GAIN OUTPUT FILTEROUTPUTS
Figure 1.1: The front panel of the SR446.
WARNING
AC POWER
USB
Stanford Research Systems
CHASSIS
GROUND
MODEL SR446 Programmable Gain Preamp
Designed and Assembled in the U.S.A.
90 264 VAC, 47 63 Hz
15 W (max)
− −
No user serviceable parts inside. Refer to operation manual for
safety notice. For use by qualied laboratory personnel only.
Figure 1.2: The rear panel of the SR446.
The front panel user interface (see Figure 1.1) displays the complete
state of the instrument. All conguration seings can be performed
either through the front panel directly, or remotely through the USB
interface located on the rear panel (see Figure 1.2). A connect indicator
shows when the remote USB interface is connected and ready for
communication. An error indicator illuminates if any remote command
errors have occurred, and will remain lit until the STAT? query is
executed. The power standby indicator shows that the AC main power
is connected and the SR446 is ready to be turned on.
SR446 400 MHz Programmable Gain Preamplier

1.2 Using the SR446 9
1.2 Using the SR446
The SR446 400 MHz Programmable Gain Preamplier can be congured
easily by using the 7 front‑panel buons. Seings are stored in non‑
volatile memory and restored upon power‑up.
AC/DC
Vin
–Vout
Prog.
Gain
Diff.
Amp
Prog.
Filter
+Vout
OL
Protect
OL Protect
×
2
×
-
2
Signal
/GND
50 Ω
500 Ω
50 Ω
50 Ω
Figure 1.3: SR446 block diagram.
1.2.1 Input
Operation of the SR446 is described by the simplied block diagram
(Figure 1.3). Input coupling is either DC ,AC , or GND , and is
selected by pressing the [Couple] buon. AC coupling is through a
100 nF capacitor, giving a 16 kHz 3 dB corner frequency when driven
by a 50 source, AC coupled, with Term set to 50 . See the ICPL
remote command (§2.3.5, pg 18).
Following the AC coupling stage, the input impedance is switched
between 50 or 500 by pressing the [Term] buon. The 500 
seing can be used to provide a higher transimpedance gain for charge
and current sources—such as photomultiplier tubes—that may be
useful when the amplier is located close to the signal source. Although
the input has protection circuitry against electrostatic discharge, users
must avoid applying continuous input signals beyond 4 V to avoid
damaging the amplier front‑end components. The 50 impedance
seing is intended to terminate 50 coaxial cable such as RG‑58. See
the INPZ command (§2.3.5, pg 18).
The amplier performs best when both outputs are terminated into 50 
loads. Do not leave unterminated cables connected to the outputs, as
this can lead to oscillation of the amplier. The overload indicator shows
if any output signal is over the limits or beyond the linear operating
range of the instrument. See the OVLD? query command (§2.3.9, pg 20).
SR446 400 MHz Programmable Gain Preamplier

10 1 Operation
The SR446 can reject a DC bias voltage on the input, as well as unwanted
low frequency signals, by using the AC coupling mode. The cuto
frequency is around 16 kHz when set to 50 termination and driven
by a 50 source. When the input coupling is set to GND, the amplier
front‑end circuitry is disconnected from the input BNC and internally
shorted to ground. Note that the input loading at the BNC is not
changed when congured to GND.
1.2.2 Gain
Gain of the SR446 is displayed in either dB or V/V units, selected by
the [Units] buon. See the UNIT command (§2.3.6, pg 18).
Gain can be adjusted from +0 dB (1) to +40 dB (100) in 2 dB steps, by
pressing the GAIN or . See the GAIN command (§2.3.6, pg 18).
1.2.3 Output lter
The full bandwidth (3 dB) of the SR446 is 400 MHz. In many situations,
users may wish to reduce the output bandwidth. This can be helpful
to block unwanted high‑frequency components of an amplied input
signal, as well as to reduce the overall output noise for low‑bandwidth
applications.
The output lter provides three reduced output bandwidth seings,
200 MHz ,100 MHz , and 20 MHz in addition to the full bandwidth
full BW seing. The lter seing is selected by pressing OUTPUT
FILTER or buons. See the BNDW command (§2.3.7, pg 19).
SR446 400 MHz Programmable Gain Preamplier

1.3 Special operations 11
1.3 Special operations
1.3.1 Oset calibration
The SR446 has an automatic oset calibration feature that will trim the
input oset voltage to within 1 mV of zero after operation. To trim the
DC oset:
1. Ensure the unit has been on for at least 30 minutes to warm up.
2. Disconnect cables from the input and both output ports.
3. Select input grounded by pressing the [Couple] buon until GND
is illuminated.
4. With the GND indicator illuminated, press and hold the [Couple]
buon until the display shows 



cAL .
5. Release the [Couple] buon.
The display will show a countdown while each gain conguration is
separately trimmed and recorded to non‑volatile memory. When the
procedure has completed, the display will briey show 



End . See the
OCAL command (§2.3.8, pg 19).
1.3.2 Factory reset
Restoring the factory default seings of the SR446 will erase all
user seings and return the instrument to the *RST conguration.
Additionally, any trim data from oset calibration (see section 1.3.1,
above) is erased and returned to the original factory calibration. See
the FRST command (§2.3.8, pg 19).
To initiate a factory reset from the front panel:
1. Turn o the unit.
2. Press and hold the [Couple] buon, and then press the [POWER]
buon while continuing to hold [Couple] depressed.
3. The display will show 



rSt
4. After about 5 seconds, the unit will return to normal operation.
SR446 400 MHz Programmable Gain Preamplier

12 1 Operation
SR446 400 MHz Programmable Gain Preamplier

13
2 Remote Operation
This chapter describes operation of the SR446 400 MHz Programmable
Gain Preamplier via the remote interface.
2.1 List of Commands by Subject . . . . . . . . . . . . . . . 14
2.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2.1 Interface Conguration . . . . . . . . . . . . . . . 15
2.2.2 Buers . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3 Commands . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3.1 Command Syntax . . . . . . . . . . . . . . . . . . 16
2.3.2 Notation . . . . . . . . . . . . . . . . . . . . . . . 16
2.3.3 Examples . . . . . . . . . . . . . . . . . . . . . . . 16
2.3.4 Interface Commands . . . . . . . . . . . . . . . . 17
2.3.5 Input Commands . . . . . . . . . . . . . . . . . . 18
2.3.6 Gain Commands . . . . . . . . . . . . . . . . . . . 18
2.3.7 Filter Command . . . . . . . . . . . . . . . . . . . 19
2.3.8 Utility Commands . . . . . . . . . . . . . . . . . . 19
2.3.9 Status Commands . . . . . . . . . . . . . . . . . . 20
SR446 400 MHz Programmable Gain Preamplier

14 2 Remote Operation
2.1 List of Commands by Subject
Interface
*IDN? ............Identify..........................................17
*RST .............Reset............................................17
Input
ICPL(?) {i}........InputCoupling..................................18
INPZ(?) {i}........InputImpedance................................18
Gain
UNIT(?) {i}........DisplayUnits....................................18
GAIN(?) {i}.......Gain.............................................18
Filter
BNDW(?) {i}......OutputFilter....................................19
Utility
OCAL(?) ..........OsetCalibration................................19
FRST.............FactoryReset....................................19
Status
OVLD? ...........Overload........................................20
STAT? ............StatusFlags......................................20
SR446 400 MHz Programmable Gain Preamplier

2.2 Introduction 15
2.2 Introduction
Remote operation of the SR446 400 MHz Programmable Gain Preamplier
is through a simple command language documented in this chapter.
Both set and query forms of most commands are supported, allowing
the user complete control of the unit from a remote computer through
USB.
Where applicable, the corresponding front‑panel interface to each
command is also indicated. Most instrument seings are retained in
non‑volatile memory. Upon power‑on, these seings are restored to
their values before the power was turned o. Where appropriate, the
default value for parameters is listed in boldface in the command
descriptions.
2.2.1 Interface Conguration
The USB interface is implemented as a serial port emulator, with xed
data rate of 115,200 baud, 8 data bits, 1 stop bit, no parity, and no ow
control.
The Connect indicator illuminates whenever a USB connection is active.
The Error indicator illuminates after a remote command error, and can
be cleared by the STAT? query.
2.2.2 Buers
The SR446 stores incoming bytes from the remote interfaces in separate
500‑byte input buers. Characters accumulate in the input buer until
a command terminator (the CRbyte) is received, at which point the
message is parsed and queued for execution. Query responses from the
SR446 are buered an a 500‑byte output queue.
If the input buer overows, then bit 0 (unknown command) is typically
set in the STAT? register, the buer is cleared, and the instrument
continues to process new commands.
SR446 400 MHz Programmable Gain Preamplier

16 2 Remote Operation
2.3 Commands
This section provides syntax and descriptions for remote commands.
2.3.1 Command Syntax
The four leer mnemonic (shown in CAPS) in each command sequence
species the command. The command mnemonic is optionally followed
by one parameter.
Many commands may take either set or query form, depending on
whether the ?character follows the mnemonic. Set only commands
are listed without the ?, query only commands show the ?after the
mnemonic, and optionally query commands are marked with a (?).
Parameters in {} are required to set a value, and must be omied for
queries.
Do not send ( ) or {} as part of the command.
Each command must be separately terminated with the CRcharacter.1
Null commands and duplicate whitespaces (including the LFcharacter)
are ignored. Execution of the command does not begin until the command
terminator is received.
2.3.2 Notation
Symbol Denition
iUnsigned decimal integer
(?) Required for queries; illegal for set commands
{var} Required parameter for set commands; illegal for queries
2.3.3 Examples
Each command is provided with a simple example illustrating its usage.
In these examples all data sent by the host computer to the SR446 are
set in upright teletype font, while responses received by the host
computer from the SR446 are set in slanted teletype font.
The usage examples vary with respect to set/query, optional parameters,
and token formats. They are not exhaustive, and are intended to provide
a convenient starting point for user programming.
1The SR446 does not support compound (”;”) command formats.
SR446 400 MHz Programmable Gain Preamplier