Neuroplex Inc.

Offering Custom Solutions for Research

 

Preamplifier Modules 

 

PA 01 Sixteen Channel Preamplifier /Band Pass Filter Module

This low cost system module is designed to receive signals from the HB04 BW/SSS head stage cables assemblies that provide 16 high input and unity gain signals from pairs of eight micro wire recording probes.  A reference input channel of the PA -01 receives input from a 17th single preamp used for sampling ground from the HB04 head stage.  Sampling ground allows local referencing to minimize noise to be carried out at the input of the preamplifier with gain. The PA-01 preamplifier module provides gain and a fixed band pass filter between an electrical interface between an array of recording probes and a digitizing recording system.  Output from the PA01 is provided by balanced twisted pair signals to allow low-noise transmission over distance. 

Sixteen channels of pre amplification are provided at 200x gain and with a band pass filter fixed at 500 Hz high-pass and 5 kHz  low-pass, standard for neuron spike event recording.  These settings provide t typical values to capture neuron spike waveforms from neuron spike trains.

Power for the PA-01 is to be provided at + 10 volts, and ground from Biographics PS-1 Power module.  The PA-01 conditions andprovides low noise power to the HB04 head stage units as + and 2.5 V and GND through a transition unit consisting of a 26 lead flat input connector cable and DB25 plug.

 

Available Band-pass settings include:

500 HZ to 6 KHZ - for typical spike potentials

2 HZ to 120 HZ for EEG

20 HZ to 1200 HZ for EMG and EKG

User may specify special settings.

 

PA-02 Sixteen Channel Preamplifier with Gated-Input Artifact Suppression

Artifact Suppression Strategies:   Artifacts are created in multiple forms when stimulation pulse transients reach the recording probes.  Normally artifacts from various sources produce waveforms that are rejected during spike sorting, but problems can arise if the artifacts arrive at the same time as the spikes or signals of interest. Even very small deviations from the normal spike waveforms sampled by the A to D converters can result in errors in spike sorting operation.    Large artifact signals may temporarily overload either the head stage unity gain preamplifier or the later stages of the amplifier filters that provide gain and band pass filters actions. 

Artifact suppression can be provided in multiple independent ways.  Each has advantages and each has limitations.  The PA-02 Preamplifier/Filter allows the stimulation timing pulses to be applied to a circuit at the input to the preamplifier, which transiently disconnects the unity gain signal from the later preamp/filter circuits.  This strategy is effective in preventing a large artifact signal from overloading the later stages. Overload at any stage in the chain of amplifiers tends to result in long lasting voltage deviations, one to two msec, from baseline that obstructs spike detection.  Small artifact signals can sometimes be corrected by digital subtraction at a later stage of analysis by the DSPs.  Extremely large artifacts that overload the head stage unity gain pre amplifiers for a time may be not correctable.  Stimulation through wires located near to recording arrays usually yields a combination of large and small artifacts.

 

Description:  This preamplifier system provides artifact suppression capabilities to a band pass preamplifier for spike detection by transiently blocking signals at the input.  The PA-02 preamplifier module is a 16-channel low-noise gated preamplifier system with fixed bandwidth and gain.  Normal settings are 500 HZ and 5KHZ.   An additional jumper-selectable gated reference input allows for subtraction of common-mode voltages from the 16 inputs before amplification.  This input normally receives input from a seventeen preamplifier output provided by the HB04 head stage that samples ground at the head of the animal.  Artifact suppression carried out by providing a pulse input at the time that simulation is applied to the subject.  This pulse is used to transiently disconnect the inputs arriving from the head stage from the amplifier filter chain.  Large transient signals are prevented from overloading the filter amplifiers, an event that may take several msec for recovery to baseline. 

All sixteen input gate switches are triggered by an opto-isolated external signal, and maintain an OFF state for a time settable by binary-weighted switches on the card edge.  Multiple PA-02 boards can be triggered from one gate input.   The board also provides multiple switch-selectable headboard power settings, and a configurable gate output signal to drive external circuitry. 

Power is provided from the PA-01 and PA-02 Preamplifier modules to the HB04 head stage units as + and 2.5 V and GND through a 26 lead flat input connector cable and DB25 plug.  Optional settings for head stage power are switch selectable. Power to the PA-01 is to be provided at +  10 volts, and ground from Biographics PS-1 Power module.

 

Preamplifier PS-1 Power Module:  This unit provides exceptional regulation and isolation of + and 10 V with GND.  It is capable of powering eight modules of PA-01 or PA-02.