Bandpass delta-sigma modulator with 800 MHz center frequency

A fourth-order bandpass /spl Delta/-/spl Sigma/ modulator with center frequency of 800 MHz designed and fabricated in AlGaAs/GaAs heterojunction bipolar transistor (HBT) technology is reported. The modulator can be clocked at a continuum of frequencies from 2-4 GHz. Its performance was characterized at one convenient clock frequency, 3.2 GHz, since clocking the modulator at 4 times the center frequency allows for trivial extraction of in-phase and quadrature components of the bandpass signal in the digital domain. The 1-bit modulator output achieves a signal-to-noise ratio of 66 dB over a 100 kHz bandwidth and 41 dB over a 25 MHz bandwidth (which covers the entire cellular band).