A low-power direct IQ upconversion technique based on duty-cycled multi-phase sub-harmonic passive mixers for UWB transmitters

This paper presents a low-power direct-conversion IQ modulator for ultra-wideband (UWB) communications based on multi-phase duty-cycled sub-harmonic passive mixers. The novelty of the proposed architecture is in employing a quadrature mixer array in such a configuration that the upconvertion of the baseband signal can be performed using a much lower LO frequency, i.e., a sub-harmonic frequency of the carrier. As a result, several benefits can be gained. Requiring a sub-harmonic LO (SHLO) relaxes the requirements on the frequency synthesizer circuitry. Moreover, the need for digital power-hungry or analog inductor-based high frequency LO buffers is alleviated. In addition, since rail-to-rail LO signals can be provided easier and with less power consumption at lower frequencies, passive mixers can be employed in the mixer array to improve the power consumption and linearity of the overall transmitter. Multi-phase LO clocks required by the proposed scheme are provided using a delay-locked loops (DLL). The proposed architecture is utilized in design of a WiMedia-UWB direct-conversion TX in a standard 65-nm CMOS technology. The Monte Carlo simulation results indicate a mean LO leakage of -68 dBc and sideband rejection of -39 dBc. The overall system draws 6.8 mA from a 1.2-V supply.