SIMTEC M-31 User manual

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M-

MODULAR AMPLIFIER

INSTRUCTION MANUAL

Serial Number

Simtec Ltd.

Cable: Simatom

3400 Metropolitan Blvd. East.

Tel. : (514) 728-4527.

Montreal 38, Quebec

Canada.

Printed in Canada

05661\1310

Warranty

Simtec equipment is warranted against defective

materials and workmanship for one year.

Queries regarding this warranty should be directed

to your Simtec Technical Representative.

The serial number and model of your unit should be

stated to your Simtec Representative when making enquiries.

Many faults may be dealt with in the field, with the benefit

of minimum down-time for your equipment.

Simtec reserves the right to adjust specifications

and prices without notice.

This publication copyright

1966 reserved by

Simtec Ltd., Montreal, Canada. No part may be reproduced

without permission of the copyright owner.

.25

.125

.063

FINE GAIN

COARSE GAIN x8

FIRST DIFFERENTIATOR

.65

.70

.60

.25

1.0

•

1.125

.85

.063

.90

8 64

128

B.B.

256

.55.

.50

SECOND DIFFERENTIATOR

OUTPUT POLARITY

DIRECT

INVERTED

INTEGRATOR

B.B.

BUFFER SECTION

UPPER CONTROL

LOWER CONTROL

IN IN

OUT

A.C.OUT

)10

93ohms

NORMAL

44)

TERM. OFF

NO CONN.

NO CONN. D.C.

OUT (i.)

MODULAR AMPLIFIER M-31

Figure 1. SIMTEC M-31 MODULAR MAIN AMPLIFIER

Type M-31 Modular Main Amplifier is shown on the

opposite page with its controls and switches in a standard

position. With the toggle switches (Si to S4) in the normal

upward position, the preamplifier signal is introduced at the

first BNC connector on the left (J1) and, after amplifying

and shaping within the amplifier, is taken out at the extreme

right either by

a.c. coupling

(the upper connector J7) or by

direct coupling, (the lower connector J8).

The input termination switches (Si and S2) are shown

in the upward or terminated position suitable for most pre-

amplifiers. When in downward position each gives 1000 ohms

input impedance.

Controls in the Upper Control section are shown

with Fine Gain at 1.0, the maximum; the Coarse Gain knob

(outer) is shown at

and the First Differentiator at 1 micro-

second.

In the Lower Control section, the Output Polarity is

set to Direct, giving the same pulse polarity at both input and

output of the M-31; the Integrator control is set to 1 micro-

second and the

Second

Differentiator is set to Broad-Band, thus

giving a monopolar pulse.

When

the controls are set as above,

the noise relative to the input is less than 15 microvolts.

(For detailed explanation of the control functions,

please refer to the text.)

CHARACTERISTICS

General

The Simtec M-31 Modular Main Amplifier is a high gain audio

to radio frequency amplifier for use in shaping and amplifying

pulses from nuclear radiation detectors. Its power is drawn

normally from an AEC Standard Bin, but may be taken from many

supplies of similar specification. Pulse Shaping and amplifica-

tion are accomplished by resistor-capacitor net-works in con-

junction with high speed operational amplifiers. Successive

shaping and gain operations are performed on the pulses as they

pass through the amplifier. The sequence and nature of these

operations is chosen to optimize the signal to noise ratio and

saturation characteristics of the amplified pulses, for all

input pulse rates and signal magnitudes.

Operational Amplifiers

The individual plug-in high speed operational amplifiers

have gain-bandwidths in excess of 1500 MHz and may give closed

loop risetimes as fast as 20 volts in 35 nanoseconds; these

capabilities are relaxed in each of the six operational amplifier

positions in the interest of overall stability. The operational

amplifiers all have differential inputs, a feature which gives

high common-mode rejection for power supply disturbances and

other forms of interference. The operational amplifiers are

direct-coupled internally, a feature which gives optimum

recovery from overload and which, together with the differential

inputs, provides maximum gain stability through stabilization of

the transistor bias points.

Feedback Control

Feedback networks are used for pulse shaping and gain

determination rather than interstage attenuating networks for

the following reasons:

---Potentiometer loading effects are eliminated; thus gain and

time determining circuit elements may be given values which

are simple ratios to one another.

---Resistor-capacitor combinations may be used exclusively

in networks which synthesize transients. Capacitors have

the advantage over inductances that for wide frequency ranges

they have better phase shift and dissipation characteristics;

moreover, the quality of component required for the level of

stability achieved in the M-31 is more readily available in

capacitors than in equivalent inductances.

---Signal to noise ratio is nearly independent of gain; at

minimum gain, signal to noise ratio of the amplifier with

gain control in the feedback loop is much superior to that

for the amplifier with interstage attenuators, because with

the former the noise of the gain stage is reduced in propor-

tion to the signal, but not with the latter.

---Gain stability is not favored by amplifiers with interstage

attenuators and filters; loading effects on interstage net-

works demand that these networks see constant impedances at

both input and output. When gain and shaping are determined

by feedback networks, these computing networks are not loaded

by the surrounding circuitry and no instability can result

from this source.

Front Panel Arrangement

Each section of the M-31 is provided with controls and/or

connections on the front panel of the AEC standard four-width

module. In the schematic diagram, BNC connectors are numbered

from left to right on the front panel, as are the switches.

Connections marked "Buffer Section" are associated with Opera-

tional Amplifier No. One. Connections marked "Upper Control"

are associated with Operational Amplifiers Two and Three; this

group is controlled by the "First Differentiator "and" Coarse

Gain" rotary switch, and by the "Fine Gain" potentiometer

to its left. Connections marked "Lower Control" are associated

with Operational Amplifiers Four, Five and Six; this group is

controlled by the "Integrator" and "Second Differentiator"

switch and by the "Polarity" switch to its left.

Power Requirements

The M-31 requires about

8.4

watts of D.C. power as follows:

24 volts at 150 ma and ± 12 volts at 50 ma. This power is

available from any modular power supply of The NBS/AEC standard

type (per TID 20893, Louis Costrell) or of The Lawrence

Radiation Lab.

Linear Amplifier 11x198 type of bin supply

(Goulding and Landis design,

used by

several

manufacturers).

Ripple and regulation specifications

of either

of these types

of supplies are adequate for

most high

quality spectroscopy.

Power decoupling and gain stabilization within the M-31 permits

use with a wide variety of supplies.

When used without an AEC Standard Bin, The noise suppression

and shielding precautions within the M-31 are adequate for most

use on the bench, or in a nonstandard rack mount.

Power Connections

The mating connector required is an AMP No. 202516-3, 42

pin female block, with AMP "Type III

" Socket contacts mounted

as follows:

Pin number 16 12 volts

17 - 12 volts

28 4- 24 volts

29 - 24 volts

34 - GROUND.

Shielding of the nonstandard cable may or may not be required,

depending on the severity of the RFI environment.

Grounding

For optimum system noise performance, a certain minimum

of care must be taken with the grounding. Precautions advised

are:

Make sure that grounds for the preamplifier, detector

bias supply and M-31 are

to being the same ground,

when the single input is used; and

when ground at the preamplifier is "exported" through

a cable for common mode rejection of pickup, try to match

the cable lengths and source impedances as exactly as

possible for minimum readjustment of RVI and

common

mode trimmers.

Construction Features

The M-31 fits four module widths (5.4 inches) of a standard

AEC bin. It consists of ten major assemblies as noted on the

system schematic. Six of

these

assemblies are the six opera-

tional amplifiers which are plug-in units mounted in individual

shield cans over 22-pin edge connectors. The edge connectors,

in turn are mounted on a common assembly called the "mother

board" which contains the bulk of passive components not mounted

on the Upper or Lower Control rotary

switches.

Each operational amplifier

has

a small hole near the top

end which permits removal for servicing or inspection.

Each transistor is socket mounted, also for ease of inspection

or replacement should the need arise.

Each of the three major outputs has a spare high stability

resistor mounted on the mother board as indicated on the system

schematic. This feature permits the user to mount extra

connections on front or back panel of the module at a later time

should the need arise. The common source impedance directly on

the output of each operational amplifier is less than 0.1 Ohm

when two or more such loads are used.

All semiconductors used in the M-31 are silicon units, unselected.

All precision resistors surpass specification MIL-R-10509E,

Characteristic "C" or better in all gain-determining positions.

All carbon resistors are of the high-stability, high reliability,

hot molded type, surpassing performance required by specification

MIL-R-IIE, Characteristic "G".

The etched wiring boards are of high peel strength double-sided

glass epoxy laminate.

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