Stanford Research Systems SIM954 Operation And Service Manual

Operation and Service Manual

Stanford Research Systems

300 MHz Dual Inverting Driver Amplifier

SIM954

Revision 1.01 • February 4, 2010

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., 2008 – 2010. All rights reserved.

Stanford Research Systems, Inc.
1290–D Reamwood Avenue
Sunnyvale, CA 94089 USA
Phone: [phone] • Fax: [phone]

www.thinkSRS.com • e-mail: [e-mail]

Printed in U.S.A. Document number 9-01649-903

SIM954 300 MHz Dual Inverting Driver Amplifier

Contents

General Information iii

Safety and Preparation for Use . . . . . . . . . . . . . . . . iii

Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . iv

1 Operation 1 – 1

1.1 Quick Start . . . . . . . . . . . . . . . . . . . . . . . . . 1 –2

1.2 Operation Inside the SIM900 Mainframe . . . . . . . . 1 – 2

1.3 Operation Using an External Power Supply . . . . . . 1 – 3

1.4 Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . 1 – 3

2 General properties 2 – 1

2.1 DC Characteristics . . . . . . . . . . . . . . . . . . . . 2 – 2

2.2 AC Characteristics . . . . . . . . . . . . . . . . . . . . 2 – 4

2.3 Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2– 8

2.4 Crosstalk . . . . . . . . . . . . . . . . . . . . . . . . . . 2– 9

2.5 Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . 2 – 10

2.6 Power Supply and Thermal Considerations . . . . . . 2– 12

3 Application notes 3 – 1

3.1 Resistive Loads . . . . . . . . . . . . . . . . . . . . . . 3 – 2

3.2 Capacitive Load Handling . . . . . . . . . . . . . . . . 3 – 3

3.3 Inductive Loads . . . . . . . . . . . . . . . . . . . . . . 3 – 5

3.4 Transformers . . . . . . . . . . . . . . . . . . . . . . . . 3– 8

3.5 Load Impedance Matching Examples . . . . . . . . . 3 – 10

3.6 Bridge Configuration . . . . . . . . . . . . . . . . . . . 3 –11

3.7 Typical Application: a High Voltage Isolated, Low

Noise, DC-DC Converter . . . . . . . . . . . . . . . . . 3 – 12

3.8 Common Mode EMI/EMF . . . . . . . . . . . . . . . . 3 – 16

3.9 Overdrive Behavior . . . . . . . . . . . . . . . . . . . . 3– 18

3.10 Miscellaneous Loads . . . . . . . . . . . . . . . . . . . 3– 20

4 Calibration 4 – 1

4.1 Getting Ready . . . . . . . . . . . . . . . . . . . . . . . 4 – 1

4.2 Offset Voltage and Input Bias Current . . . . . . . . . 4 – 1

i

ii Contents

5 Circuitry 5 – 1

5.1 Circuit Description . . . . . . . . . . . . . . . . . . . . 5 – 2

5.2 Parts Lists . . . . . . . . . . . . . . . . . . . . . . . . . 5 –4

5.3 Schematic Diagrams . . . . . . . . . . . . . . . . . . . 5 – 7

SIM954 300 MHz Dual Inverting Driver Amplifier

General Information

The SIM954 300 MHz Amplifier, part of Stanford Research Systems’
Small Instrumentation Modules family, is a dual, inverting, precision
wideband amplifier with up to ±10 V output voltage and 1 A output
current.

The module can be used to drive many types of light laboratory loads
which exceed the capacity of typical instrument outputs without
imposing the limitations and cost of typical high power RF amplifiers.

Safety and Preparation for Use

The front-panel BNCs are all grounded to Earth ground, the power­line-outlet ground, and the metal chassis of the module. No danger­ous voltages are generated by the SIM954. However, if a dangerous
voltage is externally applied to the module, it may be present on all
BNC connectors, the chassis, the SIM interface connector, and may
cause injury or death.

The SIM954 is a single-wide module designed to be used inside the
SIM900 Mainframe. Do not turn on the power until the module is
completely inserted into the mainframe and locked in place.

iii

iv General Information

Specifications

Performance Characteristics

Property Min Typ Max Remarks
Gain −4 (12dB) 3% max. gain error

-3dB Bandwidth 300 MHz small signal
Gain Flatness 1 dB DC to gain peak

Crosstalk

VSWR

Isolation

Slew Rate 4000 V/µs
Output Amplitude 10 V into 50 Ω
Peak Output Current 1 A into ≤ 7 Ω
Average Output Current 500 mA one channel or sum of both channels
Output Impedance 3.3 Ω
Input Impedance 50 Ω
Input Offset Voltage 1 mV user trimmable
Input Bias Current 10 µA user trimmable
Operating Temperature 0 40◦C
Power Supply Voltages −15 V,+15V
Supply Current ±1 A Internally current limited

1.2 : 1 DC to 100 MHz

1.6 : 1 DC to 300 MHz

−70dB Output to input DC to 1MHz

−40dB Output to input DC to 300MHz

−60 dB at 1 MHz

−40 dB full BW

Table 1: SIM954 Specifications

SIM954 300 MHz Dual Inverting Driver Amplifier

1 Operation

In This Chapter

Following is a short overview on general guidelines for the operation
of the SIM954.

1.1 Quick Start . . . . . . . . . . . . . . . . . . . . . . . . 1 – 2

1.2 Operation Inside the SIM900 Mainframe . . . . . . . 1– 2

1.3 Operation Using an External Power Supply . . . . . 1 – 3

1.4 Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . 1 – 3

1.4.1 SIM Interface Connector . . . . . . . . . . . . . 1 – 4

1.4.2 Direct Interfacing . . . . . . . . . . . . . . . . . 1– 5

1 – 1

1 – 2 Operation

1.1 Quick Start

The SIM954 contains two mostly independent, identical small RF
power amplifiers with a gain of −4 (12dB) into 50Ω and a −3dB
bandwidth of 300MHz. The output voltage limit of ±10V can be
achieved with a modest ±2.5V input voltage, so most test equipment
can drive a SIM954 channel to its voltage and power limits.

The module was specifically designed to drive laboratory loads like
magnetic coils, capacitors, piezoelectric and electrochemical cells,
small motors, heaters etc.. While these loads often require currents
and voltages beyond the range of many test instruments, driving
them with expensive and bulky power amplifiers generally does not
represent a satisfactory and efficient solution.

Unlike many power amplifiers, the SIM954 can operate as a precise
DC amplifier, wideband RF amplifier and driver stage for difficult
passive loads like ceramic capacitors and high Q resonant circuits. It
will stay unconditionally stable under a variety of load conditions,
and its specifications will deteriorate in a predictable manner.

The two otherwise independent amplifier channels share a common
power supply and are limited by the total power consumption per­missible for a single wide SIM module. See section 2.6 on page 2 –
12 for further discussion.

1.2 Operation Inside the SIM900 Mainframe

The SIM954 is primarily designed to work inside a SIM900 main­frame. Like all other SIM modules, it should not be hot-plugged or
removed under power.

Because of their higher current requirements, the number of SIM954
operated in a single SIM900 mainframe should be limited to a max­imum of four. The modules should be separated by at least one slot
from each other, and any other module next to a SIM954 should not
have an increased power consumption itself.

SIM modules with higher power consumption, like the SIM965 Ana­log Filter and the SIM940 Rubidium Frequency Standard, should not
be operated next to a SIM954 .

Running at its power limit, a SIM954 can heat up to approximately
50◦C. Some low power SIM modules like the SIM928 Battery Isolated
Voltage Source (because of its temperature sensitive NiMH batteries),
can not tolerate these temperatures and should not be operated in a
slot next to a SIM954 .

Precision SIM modules like the SIM910 and SIM911 Preamplifiers,

SIM954 300 MHz Dual Inverting Driver Amplifier

1.3 Operation Using an External Power Supply 1 – 3

the SIM918 Precision Current Amplifier, the SIM921 AC Resistance
Bridge, the SIM922 and SIM923 Temperature Monitor modules and
the SIM970 Quad Voltmeter might show increased temperature drift
when operated close to a SIM954 amplifier and would likely benefit
from being thermally isolated from a SIM954.

As with any other power amplifier, loads should be connected and discon­nected with the amplifier powered down to ensure safe operating conditions
for the SIM954 and the load.

Loads should be checked for their ability to handle the voltage, cur­rent and power output limits of the SIM954 .

Many BNC style 50 Ω loads, terminators and attenuators, power split­ters, mixers, etc., are at risk of being damaged by a SIM954 if no further
precautions against overload are taken.

1.3 Operation Using an External Power Supply

Unlike other SIM modules, the SIM954 has additional power supply
filtering and protection against inverse polarity conditions and is
therefor somewhat more forgiving when used with custom power
supplies. A well regulated, low noise, bipolar power source with
±15 V, ±1 A output current can be used to power a SIM954 module.

1.4 Interfaces

As with any product that relies on external power, the user is responsible to
ensure that the supply never exceeds the maximum operating voltage, that
short circuit currents are limited, and that thermal overload is avoided.

Any SIM954 used outside of a mainframe should be kept in a well
controlled thermal environment where none of the ventilation slots
are covered and the sides are at least one inch away from any other
surface.

In this manual it is assumed that the SIM954 is used inside a SIM900
Mainframe. The specifications of the module always refer to use
inside a SIM900 mainframe.

There are a total of four BNCs on the SIM954 front panel. The upper
two are the input and output of Channel 1, and the lower two are the
input and output of Channel 2. The front panel calls out the input
impedance of 50 Ω, the output impedance of 3.3 Ω and the nominal
gain of −4 (12 dB) into a 50 Ω terminated load.

Each channel has an overload indicator, and there is a single ”On”
LED on the front panel to indicate that operating voltage is applied
to the module. This is useful when the module is used outside of the

SIM954 300 MHz Dual Inverting Driver Amplifier

1 – 4 Operation

SIM900 mainframe. The ”On” LED does not indicate, however, that
the power supply voltage is correct and the power source has suffi­cient output current to power the module under all load conditions.

1.4.1 SIM Interface Connector

The DB–15 SIM interface connector carries all the power and commu­nications lines to the instrument. The connector signals are specified
in Table 1.1.

There is no microcontroller inside the SIM954 and the module does
not communicate over its serial port. However, the status/service re­quest line (-STATUS) serves as an indicator for an overload condition
which can be detected by the mainframe or the user. This signal will
be pulled to ground during an overload condition. The duration of
the pull-down state is approximately the same as the on-time of the
front–panel overload LED (approximately 0.5s).

All other RS-232 signals are unused.

Direction

Pin Signal Src ⇒ Dest Description

1 SIGNAL GND MF ⇒ SIM Ground reference for signal
2 −STATUS SIM ⇒ MF Status/service request (GND = asserted, +5 V= idle)

(Overload condition indicator)

3 RTS MF ⇒ SIM HW Handshake (+5 V= talk; GND = stop)(No con-

nection in SIM954)

4 CTS SIM ⇒ MF HW Handshake (+5 V= talk; GND = stop)(No con-

nection in SIM954)
5 −REF 10MHZ MF ⇒ SIM 10 MHz reference (No connection in SIM954)
6 −5 V MF ⇒ SIM Power supply (No connection in SIM954)
7 −15 V MF ⇒ SIM Power supply
8 PS RTN MF ⇒ SIM Power supply return
9 CHASSIS GND Chassis ground

10 TXD MF ⇒ SIM Async data (start bit = “0”= +5 V; “1” = GND) (No

connection in SIM954)

11 RXD SIM ⇒ MF Async data (start bit = “0”= +5 V; “1” = GND) (No

connection in SIM954)

12 +REF 10MHz MF ⇒ SIM 10 MHz reference (No connection in SIM954)
13 +5 V MF ⇒ SIM Power supply (No connection in SIM954)
14 +15 V MF ⇒ SIM Power supply
15 +24 V MF ⇒ SIM Power supply (No connection in SIM954))

Table 1.1: SIM Interface Connector Pin Assignments, DB-15

SIM954 300 MHz Dual Inverting Driver Amplifier

1.4 Interfaces 1 – 5

1.4.2 Direct Interfacing

The SIM954 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 the mainframe.

The mating connector needed is a standard DB–15 receptacle, such as
Tyco part # 747909–2 (or equivalent). Clean, well-regulated supply
voltages of −15 and +15VDC must beprovided, following the pin-out
specified in Table 1.1. Ground must be provided on pins 1 and 8, with
chassis ground on pin 9. The −STATUS signal may be monitored on
pin 2 for a low-going TTL-compatible output indicating an overload
condition.

The SIM954 has internal protection against reverse polarity, but there is no
overvoltage protection on these power supply pins.

The power supply must be able to provide both supply voltages
simultaneously at 1A load without significant dropout.

Failure to comply with these requirements may lead to malfunction and
possibly destruction or lasting deterioration of the module’s performance.

The SIM954 may present a significant reverse current into the power
supply when turned off or when subjected to faulty load conditions.
Other loads on the same power supply can be put at risk by this
behavior, and if necessary, additional isolation and protection in the
form of reverse diodes, zener overvoltage protection diodes, and
voltage regulators has to be established.

The SIM954 power is internally well filtered, but it is recommended to use
another set of RF beads and ceramic filter capacitors directly on the DB–15
receptacle in noise sensitive environments.

This is a standard measure for all RF amplifiers and is especially
important with an RF module like the SIM954 which can deliver up
to 1A of output current.

SIM954 300 MHz Dual Inverting Driver Amplifier

1 – 6 Operation

SIM954 300 MHz Dual Inverting Driver Amplifier

2 General properties

In This Chapter

In this chapter general properties of the SIM954 are being discussed.

2.1 DC Characteristics . . . . . . . . . . . . . . . . . . . . 2 – 2

2.1.1 DC Gain . . . . . . . . . . . . . . . . . . . . . . 2 – 2

2.1.2 Gain Error . . . . . . . . . . . . . . . . . . . . . 2– 2

2.1.3 Offset Voltage and Input Offset Current . . . . 2 – 2

2.2 AC Characteristics . . . . . . . . . . . . . . . . . . . . 2 – 4

2.2.1 Input Characteristics . . . . . . . . . . . . . . . 2– 4

2.2.2 AC Gain . . . . . . . . . . . . . . . . . . . . . . 2 – 5

2.3 Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2– 8

2.4 Crosstalk . . . . . . . . . . . . . . . . . . . . . . . . . . 2 – 9

2.5 Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . 2 – 10

2.6 Power Supply and Thermal Considerations . . . . . 2 – 12

2 – 1

2 – 2 General properties

2.1 DC Characteristics

Unlike most medium and high frequency amplifiers, the SIM954
does not compromise DC and low frequency properties to achieve
its performance at high frequencies. It behaves very much like an
ideal amplifier with finite output resistance for a wide range of loads
and operating conditions.

2.1.1 DC Gain

The DC gain of each SIM954 channel is −4 or (12 dB) into 50 Ω. This
gain is load dependent. Since the amplifier has an output resistance
of 3.3 Ω, the following formula describes the effective gain for a given
resistive load:

R

Gain(R

) = −4.264 ×

load

In particular, an unterminated SIM954 will have a DC gain of −4.264
(12.6 dB), which is 6.6% higher than the nominal terminated gain.

If the SIM954 is used to drive a 75 Ω system, the expected DC gain is
Gain(75 Ω) = −4.084 (12.2 dB).

R

load

load

+ 3.3 Ω

(2.1)

2.1.2 Gain Error

The typical gain error of a SIM954 channel is approximately 1%, and
the worst case error can be up to ±3%. With exception of a few
applications, even the worst case gain error is of little consequence.

Gain errors need to be considered when two or more SIM 954 chan­nels are connected in parallel. The two amplifiers can differ by up to
6% in their absolute DC gain, and for 10 V output amplitude this is
equivalent to a 0.6 V output voltage difference.

Since this voltage difference appears across the two 3.3 Ω output
resistors, a current of up to 0.6 V/6.6 Ω ≈ 90 mA can flow between
the two amplifier outputs reducing the static SIM954 current limit of
500 mA by approximately 18%.

The majority of amplifiers will have lower gain errors and the stan­dard deviation for the cross current is only 30 mA under mentioned
circumstances.

2.1.3 Offset Voltage and Input Offset Current

With a factory calibrated input offset voltage of less than 1 mV and
an input offset current of less than 10 µA, a DC precision of better
than 2 mV (input referenced) can be achieved in 50 Ω systems.

SIM954 300 MHz Dual Inverting Driver Amplifier

2.1 DC Characteristics 2 – 3

Users who wish to re-calibrate the input offset voltage and the input
offset current can use the procedure described in Chapter 4. De­pending on the temperature range the SIM954 is exposed to, this
procedure may slightly improve the input offset voltage.

SIM954 300 MHz Dual Inverting Driver Amplifier

2 – 4 General properties

10

0

10

1

10

2

Frequency [MHz]

30

35

40

45

50

55

60

Input Impedance

2.2 AC Characteristics

2.2.1 Input Characteristics

The SIM954 has outstanding AC input characteristics up to about
100 MHz with input VSWR not excedding 1.2 : 1. Between 100 MHz
and 300 MHz, the amplifier’s input impedance falls to a minimum
of 30 Ω and a worst case VSWR of 1.6 : 1. At the worst frequency,
which is just slightly above the −3 dB point, the input has a 0.25 re­flection coefficient or −12 dB return loss. Since the non-ideal input

Figure 2.1: Typical SIM954 input impedance

impedance will reflect part of the incoming signal energy at high fre­quencies, it is necessary to either terminate the source output or keep
the cable to the SIM954 input short. To maintain the best possible
pulse response at 300 MHz (λ

= 0.67m = 26”) the maximal cable

RG58

length is 8.3 cm or 3.3”, which is a λ/8 cable.

Short cables are especially important when two or more SIM954
channels are being connected in series because the driving SIM954
channel is not terminated. While two SIM954’s connected in series
by a 4” cable will still have an acceptable pulse response, the same
combination used with 12” cables will exhibit significant ringing due
to cable reflections.

SIM954 300 MHz Dual Inverting Driver Amplifier

2.2 AC Characteristics 2 – 5

10

0

10

1

10

2

Frequency [MHz]

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

VSWR

Figure 2.2: Typical SIM954 input VSWR

If optimal response at the end of an electrically long cable driven by
a nonideal source is of importance, an input attenuator can be used
to optimize the amplifier’s input impedance near the upper end of
its frequency range. By trading gain flatness against absolute gain,
satisfactory results can usually be achieved even with electrically
long cables.

2.2.2 AC Gain

The typical AC gain is very flat up to about 10 MHz and will exhibit
variations of ±0.2 dB up to 100 MHz. Beyond 100 MHz the gain will
slightly peak (< 1 dB or 12% in amplitude). Beyond the peak it will
fall off and reach its −3 dB point at about 300 MHz.

These gain variations depend on the internal compensation of the
op-amps (which are production lot dependent) and the tolerances of
the gain setting resistors in the SIM954 . Since the THS3091 op-amps
used in this module are transimpedance types, the gain peaking and
the −3 dB point are controlled by the feedback resistor.

The curves shown are based on a randomly chosen SIM954 prototype
and are characteristic for the product. However, SRS does not test
for the worst gain variation with a precision that resembles the plots

SIM954 300 MHz Dual Inverting Driver Amplifier