A Wideband ΔΣ Digital-RF Modulator With Self-Tuned RF Bandpass Reconstruction Filter

A low power, wideband transmitter architecture utilizing ΔΣ direct digital modulation of an RF carrier is presented. Spurious signals associated with direct digital-RF conversion are eliminated through integration of a self-tuned passive LC bandpass filter. The digital-RF modulator is intended for OFDM systems and can provide data rates greater than 1 Gb/s using a bandwidth of 200 MHz centered at 5.25 GHz. Measured results show that the largest modulator spur is -44 dBc. The transmitter, including LO quadrature generator, quadrature digital-RF converter, and filter circuitry, consumes 50 mW and occupies a die area of 0.56 mm2 in a 0.13μm SiGe BiCMOS process.