Switched-rc Radio Frequency N-path Filters

At 14:30 I will give a short introduction to my thesis You are most welcome to attend the introduction, the defense and the reception afterwards. Abstract Tunable on-chip Radio Frequency (RF) filtering is highly desirable for cost effective wireless communication devices. As mobile wireless devices increasingly support multiple RF-bands, tunable RF filtering is wanted. The tremendous growth of wireless communication combined with scarcely available spectrum asks for new, more programmable radio hardware. This has led to the concept of a cognitive radio capable of smart dynamic spectrum access (DSA) which asks for software-defined radio (SDR) hardware, with flexibly programmable tunable filtering. The limited dynamic range of a receiver front-end dictates the application of RF pre-filtering in front of the receiver, immediately at the antenna. This filter should reject strong out-of-band interfering signals that would otherwise block the receiver or would cause distortion components impeding reliable detection of a desired signal. Traditionally, discrete surface acoustic wave (SAW) or bulk acoustic wave (BAW) filters have been utilized as RF pre-filters. However, this adds to the size and cost of the total system. Even more problematic for cognitive radio, these filters are hardly tunable. State of the art on-chip LC filter techniques are typically limited by the low Q of spiral inductors or by the limited dynamic range in case of active Q-enhanced and gm-C filters. Hence, there is clearly an RF pre-filter research challenge. In this thesis N-path switched-RC circuits are explored, aiming for RF pre-filtering for wireless transceivers. Around the switching frequency, these circuits can be modeled as a resonator and inductor-less high-Q band-pass or band-stop filtering is possible. The filter concept fits well to SDR as the center frequency is programmable by the switching frequency, i.e. via a digital clock. As new CMOS technologies provide higher density capacitors and MOS switches with low on-resistance and low parasitic capacitance, N-path filtering benefits from Moore's law. To demonstrate feasibility, a 4-path differential switched-RC bandpass filter, an 8-path single-ended, as well as an 8-path differential bandstop (notch) filter have been implemented in 65nm CMOS technology. A mathematical analysis is presented to describe the filtering behavior as well as various imperfections for the N-path bandpass and notch filters. The implemented bandpass filter provides an in-band input referred third order intercept point IIP3 in-band >+14 dBm with compression point P 1dB,in-band >0 dBm at a noise figure NF<6 dB. The filter is tunable from 0.1-1 …