A mismatch-robust period-based VCO frequency comparison technique for ULP receivers

In this work we propose a mismatch-robust VCO frequency comparison circuit based on the absolute period-measurement of the two frequencies. The main idea of the work is to increase the overall calibration precision by employing a multiplexer in the input, thereby allowing both signals to use the same path including a single Time-to-Voltage Converter circuit (TVC). Ultimately, this would result in lower overall mismatch and better accuracy compared to the case where the current sources of the two different TVCs must be carefully matched. The simulated frequency error is found to be less than 0.8% after only 4 reference cycles. The proposed scheme is also simulated against Process, Voltage, and Temperature (PVT) variations.