Dynamic range performance of on-chip rf bandpass filters

Abstract

Despite decades of research in developing "singlechip" radio transceivers, most commercial designs continue to rely on off-chip components for RF bandpass filtering. Implementing these filters on-chip remains nearly as challenging today as it was ten years ago due to problems in meeting system requirements. Recent advances in silicon-on-insulator IC processes targeted at RF designs, however, offer the possibility of producing commercially-viable on-chip filters in the coming years using Q-enhancement techniques. This paper reviews filter implementation alternatives and dynamic range (DR) requirements, illustrating the fundamental advantages of Q-enhanced LC filters over active, inductorless, Gm-C designs. A 900-MHz Q-enhanced filter with a 20-MHz bandwidth is reported that achieves 78-dB DR in a 1-MHz bandwidth while consuming 39 mW. While still 15-to 20-dB below performance of comparable-power amplifiers and mixers, investigations of noise figure and inductor Q illustrate how future designs can correct this deficiency, bringing DR performance into the commercially acceptable range.

A differential 4-path highly linear widely tunable on-chip band-pass filter

“…Moreover, especially below 1GHz, filters based on on-chip inductors have limited Q resulting in significant insertion loss, while also consuming large die area. Q-enhanced techniques [1]- [3] can improve filter quality factor but degrade linearity and noise.…”

Active N-path Filters: Theory and Design

“…where P 1dB is the 1-dB output compression power and P n is the output noise floor [14]. It can be shown that the DR of a 2 nd order Q-enhanced LC BPF shown in Frequency dependent negative resistors [16] (c) A series LC tank with a constant series negative resistance [20] (d) A parallel LC tank with a constant negative resistance in series with its inductor [21] (e) A modified differential negative resistance [21,24].…”

“…Where η is the efficiency of the circuit, B is the bandwidth of the filter, γ is the noise excess factor of the G m cells, Q 0 is the uncompensated Q-factor of the inductor and Q is the Q-factor of the filter [14]. (2.2) tells us that increasing the raw quality factor of on-chip inductors has a great impact on the dynamic range of Q-enhancement filters [26,27].…”

“…These filters were typically off-chip, bulky and expensive which led to penalties in terms of cost, form factor and less design flexibility. The push towards single-chip solutions led to a tremendous amount of research on the integration of these bandpass filters [9,10,11,12,13,14,15,16]. Analog BPFs have been notoriously difficult to implement on-chip.…”

Switched-RC radio frequency N-path filters

“…RF active filters provide high Q and tunability. However, the linearity and noise of these filters are not good enough to be used as RF pre-filtering block after the antenna [37,38].…”