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

Abstract

In this paper, a nanopower CMOS frequency reference designed with a 0.25-µm BiCMOS process for an ultralow-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 ±10.7 % and ±6.1 %, 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.

Impulse sensitivity function-based phase noise study for low-power source-coupled CMOS multivibrators

“…There are three additional fine-tuning steps between all the measured values. Each curve has a total channel width value W of its own, which refers to the transistor matrices [13]. According In the 307.2-kHz mode the output buffer consumes almost one half of the total current, while in the 24.6-kHz mode the share of the buffer is roughly 10%.…”

“…In a similar way to the ISF method, these simulators consider a LTV system to obtain the noise power spectral density. To the best of authors' knowledge, the circuits under consideration in this paper are the first multivibrators for which the ISF-based phase noise results have been published [11][12][13], and they are further expanded in this paper. At first glance the procedure of the ISF method seems to be time-consuming, but it can be automated to a great extent, for example by using a combination of EldoRF and Matlab, after which it is quite fast and convenient to use.…”

“…In the 24.6-kHz mode drain clamping is used in the multivibrator to improve the overall oscillation frequency stability [13], as in the case of the 2.0-MHz reference. In the absence of the drain clamping, the equivalent load resistance of the 307.2-kHz mode varies less than that of the 24.6-kHz mode.…”

“…The bulk electrodes of MS4 and MS5 are connected to their sources to speed up the start-up. Tri-state buffers provide an interface between the parallel frequency references and the customized flip-flop divider [13]. The enabling of the divide-by-two operation depends on the sensor interface configuration [9].…”

“…In this paper, an illustrative 10-step procedure for applying the ISFbased phase noise study to CMOS oscillators is described, after which it is used for the two implemented frequency references. In comparison to the prior publications [11][12][13], the presentation is extended by providing new simulation and measurement results, together with a more detailed phase noise study. The rest of the paper is organized as follows: Sects.…”