Net Amps 200

The Net Amps is an integrated array of low-noise amplifiers designed specifically for dense sensor array (64-, 128- and 256-channel) electroencephalographic recording of human brain electrical activity.

Each Net Amps contains the analog and digital circuitry necessary to amplify extremely low-level neurophysiological signals, antialias filter, self-calibrate, measure electrode contact impedances, and transfer data to a host computer.

The primary amplifier circuit is a hybrid digital/analog design that provides integral digital control at several stages of the signal path.

NetAmps features include:

• AMP is completely under software control by Net Station, including power, diagnostics, and impedance measurement.

• No headbox required. The Geodesic Sensor Net is connected to Net Amps via ultra-reliable, zero insertion force hypertronics modules. This solution is much more reliable than a headbox solution and eliminates chances for errors.

Input Impedance

Because the Net Amps input impedance is high enough (200 MOhm) to maintain a favorable ratio between input impedance and electrode contact impedance, it achieves excellent EEG amplification from scalp sensors with relatively high scalp impedances (10 KOhm–50 KOhm).

The high amplifier input impedance also minimizes current flow, thereby reducing the electrode polarization detrimental to low-frequency EEG recording.

The Net Amps is thus especially well suited for use with the Geodesic Sensor Net, without any need for scalp abrasion.

Isolation

For safety, all subject connections are completely isolated from the mains supply and mains supply ground. The input instrumentation amplifiers are referenced to an "isolated common," which is also connected to the subject and is the return path for very small (nano-ampere) bias currents in the instrumentation amplifiers.

Simultaneous Digitization

In many multichannel amplifiers, sample skew occurs when multiple inputs are multiplexed to a single A/D converter for digitization. The time required for multiplexing and A/D conversion causes each input channel to be measured at a slightly different point in time. Such temporal inaccuracy is problematic for high-frequency effects (e.g., sensory ERP components or spikes) and grows worse with increasing channel counts.

To eliminate sample skew, the Net Amps incorporates sample-and-hold circuitry integrated with the multiplexing logic. All channels are sampled simultaneously, then "held" in temporary buffers until the sequential multiplexing and digitization are performed. This technique eliminates sample skew; a given sample occurs at precisely the same moment in time for all channels of the Net Amps.

Specifications

• Up to 1,000 samples per second.
• 16-bit A/D converter.
• Sample and hold for simultaneous data acquisition from all channels.
• Designed for the 10K to 50K scalp impedances of the Geodesic Sensor Net.
• Engineered for low noise (0.6µV RMS typical).
• Expandable up to 256 channels.
• NetAmps 200, 128 and 256 comply with applicable European, North American, Canadian, and Japanese safety and EMC standards [EN 60601-1, CSA 22.2 No. 601.1, CSA 22.2 No. 601.2.26, UL 2601-1, IEC 60601-2-26, EN ISO 9001, and EN 46001].
• CE certified.
• CE certified under the Medical Device Directive.
• NetAmps 200 is a component of the Geodesic EEG System 200 which carries the US FDA Pre-market 510K Clearance, Canadian Medical Device License (Homologation d'un instrument medical), European CE Certification and Japanese Yakuji Approval.