Multichannel Systems PGA Manual - Manual (Page 16)

PGA Manual
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4.2 Signal Amplification and Filters
The PGA combines a band pass filter and the signal amplification in one instrument.
Different filter settings are used for different applications to enhance the signal-to-noise ratio.
The pass band of the filter amplifier should be chosen according to the signal type. It is generally
useful to set the upper limit of the amplifier near the highest expected signal frequency, but also
at a safe distance to make sure that the full gain is used for signal amplification. The PGA is
available with a standard bandwidth of 1 to 5000 Hz, which is suitable for most applications.
A bandwidth of 10 to 5000 Hz is optional, which has the advantage that the amplifier is more
stable towards low-frequency noise and oscillations, but has the disadvantage that slow signal
components such as plateaus are removed from the input signal. Other bandwidth configurations
are available on request. The PGA1632 and the PGA3264 are special versions that feature two
different pass bands. Signals are split and the two pass bands are send to two separate output
channels. For 16 input and 32 output channels, or 32 input and 64 output channels, respectively.
These amplifiers are perfect for recording signals with different frequencies: You can record slow
signals like field potentials with a bandwidth of 1 to 300 Hz on one half of the channels, and fast
signals like spikes with a pass band of 300 Hz to 5 kHz on the other half. Please refer to the label
on the amplifier to check the bandwidth of the amplifier version that you have in use.
If you have a complete ME-System with MC_Card, you can use the digital filter of the MC_Rack
program to change the pass band and filter the raw data. This way, you are much more flexible
in designing your experiments. As a further advantage, you can see the original (not filtered)
data as well. This is especially important because all filters are known to distort signals. On the
other hand, you may need a higher sampling rate to avoid aliasing, and you will have a lower
signal to noise ratio.
The gain of a PGA can be adjusted from 10 to 5000. Usually, a total gain (of preamplifier and PGA)
of about 1000 to 2000 is used for extracellular recording of biological signals. For large signals,
for example, from whole-heart preparations, you need a lower gain to prevent a saturation of
the amplifier.
Please note that the ratio of the output signal to the input signal, that is, the gain, is not
a fixed parameter for the complete bandwidth. The gain that was specified for the amplifier, for
example, 1200 is not fully reached at the borders of the amplifier's pass band. The general rule is,
that at the lower and upper limit of the frequency band, the gain is , that is approximately
70 %, of the full gain. Therefore, you should use a bandwidth that is at a safe distance of the
signals of interest. Outside the pass band, the gain decreases with the frequency and finally
approaches zero.
For information on the gain and filters of the MC_Card data acquisition system, please see
the ME-System Manual. For more information on gain and filters in general, please refer to
standard literature or contact your local retailer.