Highly Matched TΩ Pseudo-resistors for Multi-channel Neural Signal Recording Applications
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1
ETH Zürich, Department of Biosystems Science and Engineering, Switzerland
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2
ETH Zurich, Department of Biosystems Science and Engineering, Switzerland
Motivation
To reduce drift and offset of electrodes, neural amplifiers usually employ high pass filters with very low corner frequencies (e.g., fHPF<10Hz). This approach requires huge on-chip resistances (~T½). To keep the silicon area small, "pseudo-resistors" (MOS transistors biased in the weak inversion region) are frequently used [1], but their resistance may considerably vary due to processing and fabrication spread, temperature fluctuations, and even different locations on the same chip may feature different properties. Here, specific new pseudo-resistor structures have been devised to achieve small fHPF variations.
Material and Methods
The new pseudo-resistors were implemented in a CMOS high-density MEA system incorporating 2048 readout channels [2]. Two different kinds of pseudo-resistor topologies were devised. For the 1st stage, open-loop amplifiers were used, while, for the 2nd stage closed-loop amplifiers were implemented. Aided by the current mirrors and level shifters, the first-order dependence of the overdrive voltages of the transistors inside RPR1 and RPR2 on their threshold voltages was cancelled out. Thus, RPR1 and RPR2 variations were substantially reduced, which lead to small fHPF variations. A wide range of resistances could also be realized by changing the bias currents, which could be digitally tuned with 7-bit current DACs implemented on-chip.
Results
High pass filter corner frequency (fHPF) of the the neural amplifiers tuned by pseudo-resistors were measured. The uniformity of fHPF showed the inter-channel matching of pseudo resistors across 2048 channels in the high and low frequency range.
Conclusions
Current-biased pseudo-resistors for neural signal recording applications are introduced in this work. The two new structures enable to realize very large resistances while keeping the silicon area small. Results on the transfer function of the neural amplifiers and the matching of the pseudo-resistors have been shown in this paper. The circuits were fabricated in 180nm 6M1P CMOS technology.
References:
[1] A. Tajalli, Y. Leblebici, Extreme Low-Power Mixed Signal IC Design - Subthreshold Source-Coupled Circuits, Springer, 2010.
[2] V. Viswam, J. Dragas, A. Shadmani, Y. Chen, J. Müller, A. Stettler, A. Hierlemann,"Multi-functional microelectrode array system featuring 59760 electrodes, 2048 electrophysiology channels, impedance, and neurotransmitter measurement units", ISSCC 2016, Session 22.8, Digest of Technical Papers, pp. 394-396 (ISBN 978-1-4673-9467-3).
Acknowledgements
Financial support through the ERC Advanced Grant 267351 "NeuroCMOS" and individual support for A. Shadmani through the FP7-MTN EngCaBra (Contract 264417) is acknowledged.
Keywords:
CMOS,
high-density MEA,
neural amplifier,
pseudo-resistor,
Neural signal recording
Conference:
MEA Meeting 2016 |
10th International Meeting on Substrate-Integrated Electrode Arrays, Reutlingen, Germany, 28 Jun - 1 Jul, 2016.
Presentation Type:
Poster Presentation
Topic:
MEA Meeting 2016
Citation:
Viswam
V,
Chen
Y,
Bounik
R,
Shadmani
A,
Dragas
J,
Müller
J and
Hierlemann
A
(2016). Highly Matched TΩ Pseudo-resistors for Multi-channel Neural Signal Recording Applications.
Front. Neurosci.
Conference Abstract:
MEA Meeting 2016 |
10th International Meeting on Substrate-Integrated Electrode Arrays.
doi: 10.3389/conf.fnins.2016.93.00090
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Received:
22 Jun 2016;
Published Online:
24 Jun 2016.
*
Correspondence:
Dr. Vijay Viswam, ETH Zürich, Department of Biosystems Science and Engineering, Basel, Switzerland, vijay.viswam@bsse.ethz.ch