11.4 A Gm-C RF Quadrature-Current-Generation Technique with 40dB IRR in 0.65V 2mW Multi-Mode CMOS GNSS Receiver

For wearable devices such as GNSS bracelets and BLE headsets, the pursuit of lowering power consumption is an everlasting research topic [1]–[5]. Innovated topologies and circuit structures have been presented in many works aiming to lower working current and accommodate ultra-low supply voltage [6]–[12]. Among those efforts, a signal-quadrature receiver often exhibits higher power efficiency than an LO-quadrature topology, as the VCO frequency is halved and the LO quadrature 2-divider along with the LO buffer is eliminated [13]. However, the $\mathrm{I}\&\mathrm{Q}$ phase accuracy of the conventional signal-quadrature approaches illustrated in $\text{Fig}$. 11.4.1 (a-c) are vulnerable to the parasitic capacitances and impedances [14]–[19]. Moreover, the phase and amplitude imbalances are challenging to calibrate using signal-engaged switches due to the switches' inherent parasitics.