Headstage
A headstage is the small electronics module that plugs into the probe package connector and amplifies, filters and digitizes the extracellular potentials from every electrode site at the head, so that only digital data runs down the cable to the acquisition system.
NeuroNexus headstages are built around a low-power neural recording ASIC — an Intan RHD chip for recording, an RHS chip for recording and stimulation — that integrates the amplifiers, programmable filters and a 16-bit analog-to-digital converter on one die. Input-referred noise is about 2.4 µV rms; each channel is sampled at up to 30 kS/s; the pass-band is set in software, from below 1 Hz for field potentials to several kilohertz for spikes.
Digitizing at the head keeps the analog path to a few millimeters, which is what holds the noise floor near the chip's own figure, and it makes the cable independent of the channel count: one micro-HDMI or SPI link whether the probe has 16 sites or 128. The chip also measures each site's impedance in place, which is the check probe setup begins with, and samples an on-board accelerometer, where fitted, on the same clock as the neural data. Record-and-stimulate headstages pass current through the recording array for closed-loop and microstimulation protocols.
The headstage is chosen with the package, because the package connector fixes which headstage mates to it. X-Series headstages, engineered and manufactured by Kontex and commercialized by NeuroNexus, weigh 0.9 to 1.5 g with a micro-HDMI probe side, in record-only models with an accelerometer and stim-record models without, 16 to 128 channels. SmartLink headstages, engineered and built by NeuroNexus, take the package's own connector — DIP, Omnetics, ZIF or Samtec — with no adapter, at 16, 32 or 64 channels, for acute and bench work. The DAQ chip entry covers the ASICs themselves.
Typical values
| Chip | Intan RHD (record) or RHS (record and stimulate), low-power ASIC |
|---|---|
| Input-referred noise | about 2.4 µV rms |
| ADC | 16-bit, up to 30 kS/s per channel |
| Pass-band | software-set, below 1 Hz to several kHz |
| X-Series | 0.9 to 1.5 g · 16 to 128 ch · micro-HDMI · Kontex-made |
| SmartLink | 16, 32, 64 ch · direct connector mate · 2.0 g · NeuroNexus-made |
References
- Intan Technologies — RHD Recording Headstages
- Intan Technologies — RHD2000 Amplifier Chips
- Open Ephys — Acquisition Board: Headstages
- Harrison & Charles (2003) A low-power low-noise CMOS amplifier for neural recording applications. IEEE JSSC 38(6):958–965
- Harrison (2008) The design of integrated circuits to observe brain activity. Proc. IEEE 96(7):1203–1216