g.USBamp: Specs & Features

Input channel properties

g.USBamp uses wide-range DC-coupled amplifier technology in combination with 24-bit sampling. The result is an input voltage range of +/- 250 mV with a resolution of < 30 nV! This means that any electrophysiological signal can be recorded directly without additional hardware. Neither high electrode offset voltage nor big artifacts resulting from electrical or magnetic stimulation will saturate the amplifier inputs. This feature is an important requisite for various artifact treatment and correction techniques. The use of digital filters avoids hardware-related variations between channels. g.tec's active electrode system can also be connected directly, as well as all of our sensors (e.g. GSR, skin temperature, blood pressure, oxygen saturation, respiration effort and airflow, pulse plethysmography, acceleration, limb movements, snoring sounds, and many more).

Accuracy and data quality

Each of the 16 analog to digital converters operates at 2.4576 MHz. Oversampling 64 times yields the internal sampling rate of 38.400 Hz (per channel and for all channels!). In addition, a powerful floating point Digital Signal Processor performs oversampling and real-time filtering of the biosignal data (between 0 Hz - 2.400 Hz).
Therefore, a typical sampling frequency of 256 Hz yields an oversampling rate of 9.600. This results in a very high signal to noise ratio, which is especially critical when recording evoked potentials in the EEG or identifying small amplitude changes in high-resolution ECG recordings. You are measuring far below the noise-range of conventional amplifiers.

Add more channels or split systems

To set up a multi-channel system (32/48/64 channels), g.USBamps can be stacked. Just add another 16 channels by connecting one more unit to the system. To assure 100% simultaneous sampling of all channels, a simple "SYNC cable" is used to interconnect the devices (via a plug in the rear side). Each input channel can be used for any type of signal (electrophysiological signals or external physiological or physical sensors). On the other hand, if you have a 64 channel system consisting of 4 amplifiers, you can split the system to have 4 units available.

Test signal generation and calibration

The amplifier can generate an internal sinusoidal-, rectangular-, sawtooth or white-noise test signal. The amplitude and frequency of the signal can be modified to test the recording and analysis chain. An internal calibration unit periodically detects offset and gain values for each channel and uses these values for automatic internal correction. This technique yields the highest possible accuracy - especially critical for high resolution EEG and source derivation/localization.

Skin-electrode impedance

In order to obtain top-quality EEG recordings, the transition impedance between the skin and the electrode must be checked. The internal impedance testing unit measures the impedance for the individual electrodes and the results are displayed in the software. Bad electrodes can be identified easily and skin treatment and gel application can be performed during the impedance testing.

Software options

g.tec's philosophy is to provide a broad spectrum of software solutions for different groups of users (e.g. for engineers, researchers & scientists, physiologists, and medical staff, but also for software developers & programmers). From comfortable Windows-based recording software to MATLAB/SIMULINK and LabVIEW Highspeed Online-Processing environment and device drivers as well as APIs, you will find the appropriate tools for your application. Please see the list of related products/software below for more details. g.USBamp is also supported by some open source research communities such as OpenVibe and BCI2000. g.USBamp supports also the LSL (Lab Streaming Layer).

Important information

We give a full 5-year warranty on g.USBamp. g.USBamp is a safe certified medical device (CE and FDA) for research in humans, even for invasive recordings such as electrocorticography (ECoG). It must not be used for patient monitoring or determination of brain death. Medical diagnoses and decisions about treatment of diseases must not be based (solely) on results obtained with this device.

For ECoG and Spikes

Ad-Tech, PMT, Unique Medical and Cortec grid electrodes can be used for ECoG recordings. g.HEADstage can be used for neural spike recordings.

This figure shows EEG recordings with the g.HIamp during TMS stimulation with a TMS device from Mag&More. A g.GAMMAcap (size M) was prepared with passive g.LADYbird electrodes and the sampling rate was set to 38.400 Hz and no filters were selected. All electrode locations were prepared with abrasive gel to get a low electrode impedance. The TMS stimulation was done with a biphasic single pulse and about 300 repetitions applied with 1.1 Hz. The figure shows also the position of the TMS coil.

Beside g.HIamp, TMS can also be used with g.USBamp and g.Nautilus-PRO. The stimulation artifact with passive electrodes is typically 2 ms long, for active electrodes it is around 6 ms.