Supertech instruments LinearAmp User manual

LinearAmp
(Ver.4)
Signal Conditioner
Amplifier System
User's Manual
SUPERTECH Instruments

Comparison and general features of the LinearAmp system
In our choice there are three different amplifier systems. his booklet describes the
LinearAmp amplifier family. Our other amplifier products are BioAmp and MultiAmp
families. All of them are up-to-date, easy to use, highly reliable, microprocessor-
controlled constructions. We manufacture three different amplifier families, because
the three product lines are optimized for different application fields. Please read
through the appropriate descriptions at the website of Supertech for the details.
LinearAmp amplifier is optimized for high-precision signal conditioning tasks in
bioelectrical recording.
LinearAmp is a programmable amplifier, but it has (nearly) no sampling circuits in the
signal path at all, except the 8-pole switched-capacitor low pass filter. In other
words, it is controlled by a built-in microcontroller, or a remote computer, but it has
got only high-performance, low noise, low distortion analogue amplifier circuits. his
feature is indispensable when you use averaging techniques for processing its output
signal. he internal microcontroller and the optional digital port (which offers remote
control facility from a PC) are optically isolated from the amplifier stages. In this way
we could connect all the advantages of high accuracy analogue amplifier circuits, and
easy usage of digital control.
Although LinearAmp is programmable equipment, it does not need a separate
computer to work. According to this fact, it can be used as a stand-alone amplifier
(while possessing an optional serial port to communicate with a PC). his stand-alone
feature is very comfortable, because the computer is always given, but it should be
used to collect, and processing the experimental data. LinearAmp's microcontroller on
the front panel has got a 3-button keypad, and menu-driven internal software, so it is
very friendly to use.
he internal structure of LinearAmp is modular, so the number of the amplifier
channels, and the number of the microcontrollers built in one equipment can be
decided independently. Only the aspects of the application field should be considered
when we decide, how many amplifier channels, and how many microcontrollers will
be placed in the cage of the equipment (for example it is comfortable to use only one
microcontroller to program all the EEG channels together, but another controller
should be used, if there is a single unit channel in the system, and a third controller is
necessary, if there are further channels for ECG).
Independently of the number of the microcontrollers, every amplifier channel has got
their own DC offset correction circuits, even in a multi-channel system. he voltage
range of the offset correction is +/- 200 mV, with 0.1 mV of resolution. In our
choice there are two different solutions for the offset correction circuit. One of them
is the analogue version with a 10-turn helical potmeter and a digital panelmeter on
the front of the equipment. he other version is the digital realization of the same
task: a separated microcontroller, dealing with the numerical control of the offset
voltage. he actual version should be specified in the order.

Technical data
One of the most sophisticated features of LinearAmp is its Low Pass Filter. his
circuit is an 8-pole, Bessel-type filter with linear phase response. his special, high
quality Low Pass Filter is necessary to realize the anti-aliasing function, which is
indispensable before the analogue to digital conversion.
In the LinearAmp the High Pass Filter, the Low Pass Filter, and the Gain have got 8
possible positions. he actual values, realized during the manufacturing process can
be ordered with the default parameters, but they can be requested with special
values, to meet any special requirements, as well. he default values for the Filter
and Gain sections are listed below. Any combination of the parameters can be
selected; even the invalid settings (for instance, if the High Pass Filter is set to higher
frequency, than the Low Pass Filter). he invalid settings result no faults in the
equipment, only the output voltage will be driven to zero.
High Pass Filter settings:
DC (0 Hz)
0.16 Hz (1 s)
0.53 Hz (0.3 s)
1.6 Hz (0.1 s)
5.3 Hz (0.03 s)
10 Hz
30 Hz
100 Hz
Low Pass Filter settings:
100 Hz
200 Hz
500 Hz
1 kHz
2 kHz
5 kHz
10 kHz
20 kHz
Gain settings:
0.5
1
2
5
10
20
50
100
he Notch Filter (hum noise filter) of the LinearAmp is tuned to 50 Hz (or optionally to
60 Hz). he Notch Filter can be switched on and off in the software running on the

microcontrollers. he rejection ratio of the Notch Filter on its central frequency is 40
dB.
here is a possibility to select the full amplifier chain of LinearAmp as Inverting or
Noninverting characteristics. his selection is also a menu point of the software
running on the microcontrollers.
here is a general Bypass function in LinearAmp. It is also a programmable feature.
he Bypass function is not a simple shortcut wire switched between the Input, and
the Output connectors of LinearAmp. If the Bypass function is activated, the
equipment behaves as a voltage follower, but provides voltage swing limitation for
both polarities on the Output. his feature is useful to protect the analogue to digital
converter connected to the Output against any faulty input signals appearing on the
Input connector of LinearAmp. In extremely worst case LinearAmp behaves as a
suicide protector equipment.
If the LinearAmp is used in human experiments, an additional optical isolator circuit
should be ordered for every channel with 4 kV of isolation voltage. he optical
isolator does not modify any parameter of LinearAmp, because the isolator circuit has
got unity gain, with noninverting characteristics.
Noise
he noise level of LinearAmp was measured under the following conditions. he input
signal applied to the input of LinearAmp was generated by a battery-powered square
wave generator. he output impedance of this generator was 470 Ohms. he
measured noise voltages were referred to the input of the LinearAmp (in other words,
they were measured at the output, but they were calculated to the input, divided by
the actual Gain). he actual settings of the LinearAmp amplifier, except the Low Pass
Filter, have negligible effect for the total noise characteristics. he noise level
depends mainly on the Low Pass Filter setting. he results of the noise measurement
are:
If the bandwidth is 20 kHz (the low pass filter is opened to the widest range), the
input noise RMS voltage is less than 12 microVolts (50 microVolts peak-to-peak).
If the bandwidth is limited to 2 kHz with the low pass filter, the input noise RMS
voltage is less than 5 microVolts (20 microVolts peak-to- peak).
If the bandwidth is limited to 500 Hz with the low pass filter, the input noise RMS
voltage is less than 2.5 microVolts (10 microVolts peak-to- peak).
he difference between amplifier models mostly depends on the quality of the design.
Such features as hum noise, square wave transient response, phase response,
frequency domain characteristics, ability of parasite oscillations, thermal stability,
reliability, etc. are responsibility of the designer. But there is no real difference in the
signal to noise ratios of signal conditioner amplifiers manufactured by different firms.

he signal to noise ratio depends on the internal design of the operational (and
instrumentational) amplifier integrated circuits. he race of the smaller electronic
noise is a race of the semiconductor manufacturers. he designer can only choose
from the good amplifiers, from the leader semiconductor factories.
Ground topology
here is a general design method in the high gain amplifiers, what is applied in
LinearAmp, as well. Usually in the signal conditioner amplifiers (as in our amplifiers,
too, if optical isolators are not used) the Input GND, and Output GND points are
connected together internally. he ohmic resistance between them is less than 0.05
Ohms. However they are signed as different points, because in the interior of the
amplifier the ground network forms a linear topology, not a single-point GND (as it is
advised in the text-books). he suppression of the hum noise is better, if the ground
line follows the signal line linearly according to the increasing signal amplitudes from
the input to the output. o establish a single-point shielding ground is a good solution
at the output end of the signal ground line. Unfortunately the security ground wires
are also connected to the metal enclosures of the equipments. he security ground
wires are usually hum noise sources for the signal conditioner amplifiers (because
they usually drive some mains-frequency fault currents from other equipments, from
other rooms), but they must not be disconnected, they are compulsory to be used. If
you use a mains isolation transformer with symmetrical secondary coil, you can
eliminate the disadvantage of the security ground (if in your lab it is allowed to use,
please check the local rules). he Faraday-cage, metal parts in the Faraday-cage, the
oscilloscope, the PC, the Output GND of the amplifier, and the real, separated signal
ground line (coming from the earth directly, if it is available) should be connected to
this single-point shielding ground. But the ground point of the input circuitry should be
isolated from the shielding ground point (special care should be taken with the metal
parts close to the input in the Faraday-cage). he Input GND point of the amplifier is
used to provide a low impedance ground to the input circuitry only.
Connectors
he input and output connectors of LinearAmp amplifiers are standard BNC sockets.
Output GND is a 4-mm banana female connector. Output GND point is common to
the mains GND, the GND point of the Output BNC sockets and the metal parts of the
equipment case. he Input BNC sockets are isolated from the back plate. he Input
GND point is the GND point of the Input BNC socket(s).

Warranty
We give you full warranty service, including rest parts for the period of 5 years by
default. Longer warranty periods can also be defined and agreed (the actual
conditions should be discussed before placing the order). Usually and basically we
repair the faulty equipments in our workshop. he expense of the shipment should be
covered by our customers.
Further information sources
echnical hotline via email (all of them work):
[email protected]
[e-mail]
[email protected]
International technical hotline on the phone: [phone]
For further technical information please visit our websites. Supertech Instruments
continuously uses four websites with the same content. Please use that one, which is
easiest for you to remember:
www.superte.ch
www.supertechinstruments.co.uk
www.supertech-instruments.co.uk
www.super-tech.eu