A nanopower double-mode 1-V frequency reference for an ultra-low-power capacitive sensor interface

In this paper, a nanopower CMOS frequency reference designed with a 0.25-mum BiCMOS process for an ultra- low-power capacitive sensor interface is presented. Due to the low supply voltage of 1 V, two parallel frequency references based on source-coupled CMOS multivibrators are used to implement the two required operating modes. In mode 1, when driving a 1 pF capacitive load at 24.6 kHz, the frequency reference consumes 210 nA. In mode 2, driving the same load at 307.2 kHz consumes 660 nA, respectively. Typical simulated frequency stabilities over the temperature and supply voltage ranges in modes 1 and 2 are plusmn10.7% and plusmn6.1 %, respectively. Simulated phase noises at 10 kHz offset frequency in mode 1, and at 100 kHz offset frequency in mode 2, are approximately -67 dBc/Hz and -68 dBc/Hz, respectively.