A Biphase Modulator Circuit for Impulse Radio-UWB Applications

This letter presents a circuit to provide binary phase shift keying to ultra-wideband (UWB) impulse transmitters. The circuit is based on a Gilbert-cell multiplier and uses active on-chip balun and unbalanced-to-balanced converters for single-ended to single-ended operation. Detailed measurements of the circuit show a gain ripple of $\pm 1~{\rm dB}$ at an overall gain of $-2~{\rm dB}$, an input reflection below $-12~{\rm dB}$, an output reflection below $-18~{\rm dB}$, a group delay variation below 6 ps and a $-1~{\rm dB}$ input compression point of more than 1 dBm in both switching states over the full 3.1–10.6 GHz UWB frequency range. A time domain measurement verifies the switching operation using an FCC-compliant impulse generator. The circuit is fabricated in a $0.8~\mu {\rm m}$ Si/SiGe HBT technology, consumes 31.4 mA at a 3.2 V supply and has a size of $510 \times 490~\mu{\rm m}^{2}$ , including pads. It can be used in UWB systems using pulse correlation reception or spectral spreading.