Self-Tuning OTA-C Notch Filter with Constant Q-Factor

Abstract

This paper describes the design of a self-tuning OTA-C notch filter (NF), based on a phase control loop concept. The phases of filter input and output signals are compared and the phase error is used to generate the control voltage, which adjusts the transconductances of operational transconductance amplifiers (OTAs) and, consequently, tunes the NF center frequency without quality factor variation. The proposed solution is robust to filter parameter variations. The filter is implemented in 0.13[Formula: see text][Formula: see text]m SiGe BiCMOS technology. Under the typical circuit operating conditions, the center frequency tuning is within the range from 70[Formula: see text]MHz up to 150[Formula: see text]MHz, with tuning error less than 1%. The power consumption is less than 3.6[Formula: see text]mW, the 1[Formula: see text]dB gain compression point is [Formula: see text]2.5[Formula: see text]dBm, the input (IIP3) and output (OIP3) intercept points are 3.47 and 9.07[Formula: see text]dBm, respectively, and the total filter effective noise voltage is 4.35[Formula: see text][Formula: see text]Vrms. The filter structure is suitable for complementary metal-oxide-semiconductor (CMOS) implementation.