Design and Analysis of Chopper Stabilized Injection-Locked Oscillator Sensors Employing Near-Field Modulation

This paper presents the design and the analysis of chopper stabilization circuit techniques in oscillator-based RF sensors with injection locking for dielectric spectroscopy bio-sensing applications. As the conventional phase modulation chopping scheme inevitably up-converts the 1/f phase noise intrinsically to the oscillator, we propose a near-field modulation technique that periodically shields the sensing electrical fields from fringing into the material-under-test (MUT), to achieve the desired chopping operation while avoiding the modulation of the sensor 1/f phase noise. Detailed design considerations to remedy the residual flicker noise up-conversion are discussed. The sensor prototype, implemented in 65 nm CMOS technology and operated at 16 GHz, shows a reduction in the flicker-noise corner from 10 to 0.25 kHz with field-modulation enabled, yielding a noise floor of 1 ppm in frequency shift at 10 Hz filtering bandwidth. Thermal-cycled bovine serum albumin (BSA) solutions are measured with the proposed sensor-on-CMOS. The results prove the potential for the permittivity measurements at microwave frequencies in detecting protein conformation change.