CMOS Gigahertz-Band Filters with Automatic Tuning-Circuitry
Yuyu Chang, under the guidance of John Choma, undertook the design of a tunable Gigahertz-band CMOS front-end filters with high quality factors. These have been considered one of the substantial and most challenging building blocks in transceiver design. This research proposed three aggressive gm filters and one RLC filter with Q-enhancement circuitry in this work, which essentially extend the filters' operation to gigahertz frequency range with reasonably high quality factors. A new image-reject filter is also demonstrated using this design technique. Based on tuning in the idle periods of transmission and reception, a new synchronous rectification scheme is proposed to automatically correct the resonant frequency of filters. Since this scheme directly tunes the filters, it does not have matching and tracking problems inherent in master-and-slave scheme. Furthermore, it consumes a smaller silicon area and little power. The proposed tuning scheme can also be utilized in lowpass, highpass, and notch filters. A 1.15GHz high-Q RLC filter with a synchronous rectification tuning scheme has been designed, prototyped under UltRa Lab sponsorship, and tested using digital CMOS technology. The proposed filters have significant potential for use in transceiver front-ends.
The parameters of the implemented tunable filter are as follows:
Technology: 0.5 micron CMOS
Center frequency tuning: 400 MHz to 2 GHz
Adjustable Q range: 2 to 30
Dynamic range: 40 dB
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Chip photo: Upper right-hand corner: a 1.15GHz CMOS filter with automatic tuning system.
Left-hand side: Testing circuits of inductors and MOS varactors. |
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Printed-circuit board: The designed filter IC is located at the center of the board. All radio frequency signal traces have 50 W characteristic impedance |
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The IC close-up in TQFP package |
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Testing setup of the designed filter IC at USC/Information Sciences Institute, Marina del Rey, California |
Experiments
Interference Effects