Design of a 12-bit low-power SAR A/D Converter for a Neurochip

Cutting-edge CMOS neurochips, which consist of a Microelectrode Array (MEA) manufactured on top of CMOS circuitry, allow the recording of the electrical activity of neural networks in-vitro, and their stimulation. As CMOS technology continues to scale down, signal processing is favorably done in the digital domain, which requires Analog-to-Digital Converters (ADCs) to be integrated on-chip. To relax the requirements on the neurochip’s surface temperature control system, a low-power ADC is targeted1. Among various ADC architectures, the Switched-Capacitor (SC) or Charge-Redistribution Successive Approximation Register (SAR) ADC is best suited for low power and 12-bit resolution. To avoid common-mode errors, the SC SAR ADC uses a differential topology. To decrease area, power, and cost while maintaining 12-bit accuracy, the Binary-Weighted (BW) capacitor array is split into three sub-BW capacitor arrays connected through two series capacitors. A comparator with three preamplifier stages and a latch discriminates voltage differences as small as 200μV while concurrently working with rail-to-rail input signals. The SAR control logic uses only four DFFs for the finite state machine, whereas a classical SAR implementation with shift-registers would use 12 DFFs. Furthermore, a shared register bank contains the output codes and memorizes the position of switches. The SAR ADC will be manufactured in UMC 0.18μm CMOS technology.

Joye, Neil
Leblebici, Yusuf
Shin, Sangho
Lim, Shin-Il

 Record created 2012-11-02, last modified 2018-03-17

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