TDT RZ2, Manual, Page: 291 / 736

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RA16PA/RA4PA Medusa PreAmps
RA16PA/RA4PA Medusa PreAmps
Medusa Overview
The Medusa Preamplifiers are low noise digital bioamplifiers and are available with
either PCM or Sigma-Delta As. The system amplifies and digitizes up to 16-channels
of analog signal at a 24.414 kHz sampling rate. The amplified digital signal is sent
to the base station via a noiseless fiber optic connector.
• Digitizes either four or 16 channels at acquisition rates of approximately 6,
12, or 25 kHz.
• Connects to the headstage via a DB25 connector.
• Powered by a Lithium-ion battery that provides 20 hours of continuous data
acquisition in 16-channel mode and 30 hours of operation in 4-channel
mode.
• Clip warning lights indicate when any signal is -3db from the preamplifier's
maximum voltage input.
Medusa Features
Analog Acquisition Channels
The RA16PA and RA4PA standard Medusa Preamplifiers acquire signals using 16-bit
PCM As, which provide quality acquisition with minimal delay. The RA16SD and
RA4SD use Sigma-Delta As, which have several characteristics that improve signal
quality. Oversampling of the signal before conversion removes aliasing of high
frequency RF signals.
RA16SD testing indicates that signals greater than 150% of the Nyquist frequency are
removed from the signal. This allows users to acquire at lower sampling rates (6
kHz) without worry of significant aliasing. In addition, each converter also has a
two pole anti-aliasing filter (12 dB per Octave) at 7.5 kHz. However, the sigma-
delta A’s have a fixed group delay of 20 samples (compared to four samples for
the RA16PA). When using the RA16SD this group delay must be taken into account