A 0.28mΩ-sensitivity 105dB-dynamic-range electrochemical impedance spectroscopy soc for electrochemical gas detection

摘要

An electrochemical (EC) gas sensor is a 3+ terminal electrochemical device which, when biased correctly with a potentiostat circuit, behaves as a current source whose output is proportional to the target gas concentration. The short lifetime of these sensors has become a key functional safety issue for hazardous gas detection modules. In order to predict the failure of EC gas sensors, a high precision and wide bandwidth EC impedance measurement is required [1]. For example, an electrochemical impedance spectroscopy (EIS) instrument is often used in the laboratory for failure rate analysis and there is a trend towards integration of the EIS at the chip level. However, it is extremely challenging to integrate the precision high-speed/high-power EIS with the precision low-power EC potentiostat system. For instance, [2] demonstrated a very low-power integration of the EIS and bio-potentiostat; however the EIS bandwidth is only 80Hz and the EIS dynamic range (DR) is limited at 77dB. [3] and [4] presented good EIS performance because there were no trade-off limitations between the low-power module and the high speed EIS. Furthermore, two additional challenges, not met by [2, 3, 4], are to apply an AC stimulus without disturbing the large DC potentiostat and to improve the DR for stimulus-sensitive sensors. This paper demonstrates a highly integrated SoC to support EIS applications for diverse sensors. Figure 17.4.1 shows the implemented architecture. The analog front end (AFE) and digital back end (DBE) are implemented on a 0.18μm die and a 90nm die respectively and stacked in a 5×6×1mm³LGA package. A Cortex-M3, featuring UART/SPI/I²C interfaces, is integrated in the top DBE die. The bottom AFE die has two EC potentiostat channels, with sensor readout, as well as a chip scale 0.1Hz~200kHz EIS solution, which is realized by a transmitter (Tx), receiver (Rx) and DSP. A sequencer can flexibly control all these modules through a programmable 6KB SRAM, which is shared by command memory and data FIFO.