microcontrollers. The rejection ratio of the Notch Filter on its central frequency is 40
dB.
There is a possibility to select the full amplifier chain of LinearAmp as Inverting or
Noninverting characteristics. This selection is also a menu point of the software
running on the microcontrollers.
There is a general Bypass function in LinearAmp. It is also a programmable feature.
The 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. This 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. The optical
isolator does not modify any parameter of LinearAmp, because the isolator circuit has
got unity gain, with noninverting characteristics.
Noise
The noise level of LinearAmp was measured under the following conditions. The input
signal applied to the input of LinearAmp was generated by a battery-powered square
wave generator. The output impedance of this generator was 470 Ohms. The
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). The actual settings of the LinearAmp amplifier, except the Low Pass
Filter, have negligible effect for the total noise characteristics. The noise level
depends mainly on the Low Pass Filter setting. The 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).
The 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.
