ADInstruments Bio Amp, Руководство пользователя

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Appendix A Technical Aspects
33
The signal then passes to the first non-isolated gain stage, where it is
amplified 1, 10, or 100 times. A switched-capacitor notch filter follows (this is
automatically set to 50 or 60 Hz depending on the mains frequency of your
power supply). After this, the signal passes to the final programmable gain
stage, where it is amplified 1, 2, or 5 times (or 10 times for the Dual and Octal
Bio Amps). The last part of the signal-conditioning circuitry is the low-pass
filter.
The output of the Bio Amp is buffered with an amplifier with a fixed gain
(nominally
–
1.66), to compensate for gain differences through the previous
stages of the device. An audio signal output, capable of driving headphones or
powered speakers, is provided by tapping off and buffering the output stage
(the Dual and Octal Bio Amps use two outputs).
The control for the various filters and gain stages in the Bio Amp is provided
by on-board microprocessors, which also communicate with the PowerLab
over the I
2
C bus. The high-pass filters in the Dual Bio Amp are phase-
matched to within 1° phase shift at the –3 dB frequency to allow for accurate
waveform arithmetic.
The Bio Amp Cable Input
The Bio Amp cable, for the Bio Amp and Dual Bio Amp, plugs into the six-
pin input socket on the front panel of the Bio Amp. A notch in the plug
ensures that polarity is correct. Only the supplied Bio Amp cable and lead
wires should be used as other cables may not meet safety requirements. Note
that the pin arrangement of the Bio Amp and the Dual Bio Amp is different;
the Bio Amp cables are not interchangeable. (The Bio Amp is supplied with a
3-lead Bio Amp cable, whereas the Dual Bio Amp is supplied with a 5-lead
Bio Amp cable.)
The Bio Amp has one connector: providing two pins for a differential input
signal, a separate pin for the reference, or common, signal and another
connected to the cable’s shield. The entire connector is physically and
electrically isolated to ensure subject safety.
Negative input (–)
Positive input (+)
Reference/Common
Shield
Polarising key (to
fit notch in plug)
Figure A–3
The pin assignments for
the single Bio Amp input
connector