A 0.18μm CMOS, high Q-enhanced bandpass filter with direct digital tuning

Abstract

A Q-enhanced filter is presented which operates at a high Q and employs sub-sampling and direct digital tuning. The filter is suitable as an IF filter in applications such as Bluetooth or GPS. The filter operates from 1.2V -1.8V and consumes 1.08 mW at 500MHz with a SFDR of 37 dB and a Q of 650, at 1SV. IntroductionRecent research on Radio Frequency Integrated Circuits (RFICs) has focused on the development of a fully integrated radio receiver. There is an ongoing search for architectures that can deliver high selectivity and sensitivity, all at low cost and power consumption. It is well understood that the superheterodyne architecture, with a high IF frequency, although difficult to integrate, has major advantages in terms of image rejection and selectivity (1). A major design hurdle for integrating the super-heterodyne receiver is on chip filtering.

An Accurate Automatic Quality-Factor Tuning Scheme for Second-Order <emphasis emphasistype="italic">LC</emphasis> Filters

“…The same equilibrium point and can be identified from (20) and (22). Let us identify its stability behavior using the phase-portrait concept.…”

“…Currently, available -tuning schemes for high frequency LC filters manipulate the frequency response of the filter in a digital [17]- [20] or an analog [6] feedback loop.…”

“…The scheme presented in [20] is based on direct characterization of the complete frequency response of the filter, and it is not adaptable to automatic -tuning. Finally, the VCO-based -tuning approach presented in [6] is a significant advance in the theory of automatic -tuning of LC filters.…”

“…4 can be expressed as (17) (18) where and are defined in (13) and (6), respectively. Substituting and for their expressions in (13) and (6) and defining the following variables and , (17) and (18) can be re-expressed as (19) (20) where and . Equations (19) and (20) define the differential equations of a second-order nonlinear system.…”

“…Fig. 6 shows the phase portrait of the system defined by (20) and (22) using the same filter parameters used in Fig. 5.…”