A 0.4-1.8-GHz Quarter-Rate Subsampling Mixer-First Direct Down-Conversion RF Front-End

Subsampling down-conversion has not been a popular choice for mixer-first RF front-ends for two interdependent reasons. One, the subsampling down-conversion is inherently heterodyne in nature. Two, as a consequence to one, the passive mixer transparency property can not be exploited for providing impedance matching at the RF port by impedance translation. In this work, an eight-path quarter-rate subsampling (QRSS) mixer-first direct down-conversion architecture is proposed to address these issues. The proposed architecture simultaneously achieves quadrature direct down-conversion and impedance matching by using the third harmonic of the QRSS frequency, f(s). The impedance matching is achieved by exploiting the eight-path passive mixer transparency property. Compared to RF sampling receivers, this architecture employs a sampling frequency f(s) three times lesser than f(RF), saving on the power consumption of nonoverlapping clock generation, distribution circuits, and frequency synthesizer. A test chip is fabricated in 1.2-V, 65-nm CMOS with an active area of 0.32 mm(2). The subsampling eight path mixer, baseband low-noise amplifier (LNA), and g(m)-cell consume a power of 800 mu W, 23 mW, and 3 mW, respectively, for a target bandwidth of 90 MHz. Nonoverlapping clock generation circuit consumes 2-9.2 mW, over the band 0.4-1.8 GHz. The receiver has a double sideband (DSB) noise figure of 4.7 dB, a conversion gain of 22 dB, an in-band (IB)-IIP3 of -1 dBm, and OB-IIP3 of +8 dBm.