C64 and Hawk Clinical Amplifier Systems

 

Below is information on the C64 and Hawk clinical amplifier systems. We currently use the C64 system. The Hawk amplifier will be capable of recording 128 channels for grids hopefully by spring/summer (initial release will be limited to lower channel counts — 64).

 

C64:

  1. The amplifier hardware filter BW is set at 0.016 (1.6Hz for the OR versions) to 500Hz.  The analog hardware filters do not vary.  The 500Hz anti-alias filter consists of two cascaded first order poles.  The C64 amplifier uses a sigma-delta ADC (one per channel) that limits the input bandwidth to 0.2618 of the output update rate.  The filter in the A/D is a linear phase sinc3 filter.  The following table applies:

 

Output Update Rate Input Bandwidth
1024 268
512 134
256 67
128 33.5

 

  1. The sensitivity of the C64 is set to 10mVp-p.  Although we digitize with a 22bit resolution, 16 bits are actually used by NicOne.  This puts the C64 resolution at 153nV/bit.

 

  1. The following noise levels were measued on a few channels at higher bandwidths.  Sample rate at 1024Hz looking at a 30 sec. window.

0.16Hz to 200Hz measured 3.7uVp-p, 0.56uVrms

0.16Hz to 268Hz measured 4uVp-p, 0.61uVrms

 

 

Hawk:

  1. The amplifier hardware filter BW is set at 0.048 to 11.9kHz.  The analog hardware filters do not vary.  The 11.9kHz anti-alias filter consists of several cascaded first order poles.  The Hawk amplifier uses a sigma-delta ADC (one per channel) that limits the input bandwidth to 0.492 of the output update rate.  The filter in the A/D is a linear phase FIR filter.  At lower sample rates, additional digital filtering and decimation is done in an FPGA.  The filter in the FPGA is a linear phase FIR.  The following table applies:

 

NicOne Sample Rate

(Hz)

Hardware Sample Rate

(Hz)

A/D Digital Filter

-3db (Hz)

FPGA Digital Filter

-3dB (Hz)

Analog Anti-Alias Filter

(Hz)

Combined Analog/Digital Filter

-3dB (Hz)

128 4096 2015 50 11.9k 50
256 4096 2015 100 11.9k 100
512 4096 2015 200 11.9k 200
1024 4096 2015 400 11.9k 400
2048 4096 2015 800 11.9k 800
4096 4096 2015 Pass Thru 11.9k 2015
6000 6000 2952 Pass Thru 11.9k 2946
8000 8000 3936 Pass Thru 11.9k 3920
8192 8192 4030 Pass Thru 11.9k 4014
10000 10000 4920 Pass Thru 11.9k 4900
12000 12000 5904 Pass Thru 11.9k 5856

 

  1. The sensitivity of the Hawk is set to 10mVp-p.  Although we digitize with 24bit resolution, 16 bits are actually used by NicOne.  This puts the Hawk resolution at 153nV/bit.

 

  1. The following noise levels were measured a on a few channels at higher bandwidths.  Sample rate at 1024Hz looking at a 30sec window.

0.16Hz-200Hz measured 2.8uVp-p, 0.42uVrms

0.16Hz-300Hz measured 3.7uVp-p, 0.56uVrms