Digitally Programmable CMOS Feedback ASIC for Network of Coupled Electromechanical Oscillators

This paper describes a programmable single-chip feedback ASIC for a network of coupled microelectromechanical systems (MEMS) referenced oscillators in the 0.4-15 MHz range. The chip contains differential low-noise amplifiers (LNAs), variable-gain amplifiers (VGAs) and programmable-gain amplifiers (PGAs) for gain control, second-order active-RC bandpass filters (BPFs) for band selection, all-pass filters (APFs) for phase shifting, an automatic level control (ALC) loop, and output buffers to drive mechanical resonators. The feedback transfer function can be fine-tuned via a three-wire serial peripheral interface (SPI) bus. A compensation path with its own PGAs, programmable attenuator, and APF enables removal of electrical feedthrough within the resonator. The chip has 5 differential input paths with independent gain control, 1-2 of which are used for local feedback (to realize oscillations) while the others accept inputs from other oscillators. The chip has been fabricated in 180 nm CMOS and consumes 4.6 mW at 1.8 V. In initial tests, it is integrated with a 2 MHz quartz resonator (Q = 2000) to realize an oscillator with low phase noise (-117 dBc/Hz at 1 kHz offset). Additionally, the chip's ability to synchronize oscillators is validated via a 1:1 injection locking experiment.