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A tunable, high-Q RF filter suitable for wireless transmitters has been implemented in a standard digital 0.18-mum CMOS technology. Active circuits are used to enhance the Q of two independent LC resonators, which are cascaded to form a wide bandwidth filter that can be tuned in both center frequency and bandwidth. A 5.145-GHz stagger-tuned filter with a 200-MHz bandwidth and 0.8 dB of ripple is demonstrated in an 802.11a sliding-IF transmitter. The transmitter provides spectral mask and EVM-compliant output power of -8.26 dBm for a 64-QAM OFDM signal. At lower output power, an EVM of -32.3 dB is achieved.
Date of Publication: Aug. 2009