Abstract
An active self-interference (SI) cancellation technique for SAW-less receiver linearity improvement is proposed. The active canceler combines programmable gain and phase in a single stage and is co-designed with a highly-linear LNA, achieving low noise and low power. A cross-modulation mechanism of the SI canceler is identified and strongly suppressed thanks to the introduction of an internal resistive feedback, enabling high effective receiver IIP3. TX leakage of up to −4 dBm of power is suppressed by over 30 dB at the input of the LNA, with benefits for the entire receiver in terms of IIP3, IIP2, and reciprocal mixing. The design was done in a 40 nm CMOS technology. The system, including receiver and active SI canceler, consumes less than 25 mW of power. When the canceler is enabled, it has an NF of 3.9–4.6 dB between 1.7 and 2.4 GHz and an effective IIP3 greater than 35 dBm.
Highlights
The evolution of mobile communication technologies ranging from GSM to the future 5G has continuously required increased data rates and quality of service and, in general, the miniaturization of devices and costs reduction
Off-chip Surface Acoustic Wave (SAW) filters are typically used to reject out-of-band interferers and Self-Interference (SI) signals but cause a significant form factor burden, even more so when the device operates over a large number of bands and uses multiple antennas
Much attention is focused toward SAW-less receivers, and several architectures have been proposed that are capable of tolerating large SI signals
Summary
The evolution of mobile communication technologies ranging from GSM to the future 5G has continuously required increased data rates and quality of service and, in general, the miniaturization of devices and costs reduction. The use on an auxiliary transmitter allows to achieve very high cancellation levels and bandwidths even in the presence of strong power amplifier nonlinearity It does not address the issue of transmitter noise leaking into the receiver. In the two-point cancellation architecture proposed in [18] the LNA is based on the noise-cancelling approach and is able to tolerate up to 2 dBm TX leakage power while achieving high effective OOB IIP3. RReeqquuiirreemmeennttss ffoorr FFDDDD IInn aa dduuaall aanntteennnnaa mmoobbiillee tteerrmmiinnaall,, tthhee iissoollaattiioonn bbeettwweeeenn TTXX aanndd RRXX aanntteennnnaass ccaann bbee aarroouunndd 2200 ddBB ttoo 3300 ddBB [[1177]]. AAssssuummiinngg aann RRFF SSIICC ooff 2200 ddBB iinn ffrroonntt ooff tthhee rreecceeiivveerr,, tthhee rreecceeiivveerr IIIIPP33 rreeqquuiirreemmeenntt iiss ddeeccrreeaasseedd bbyy tthhee ssaammee aammoouunntt ttoo aa mmoorree ffeeaassiibbllee vvaalluuee ooff 1111..88 ddBBmm. NNoonneetthheelleessss,, tthhee nnoonnlliinneeaarriittiieess ooff tthhee ccaanncceelllleerr aarree aallssoo vveerryy iimmppoorrttaanntt aanndd ccaann eeaassiillyy bbeeccoommee tthhee bboottttlleenneecckk ffoorr tthhee eennttiirree rreecceeiivveerr..TTooiilllluussttrraatteetthhisisisisssuuee,,wweerreefeferrtotoFFigiguurree. Notice that since both the canceler gain (α1) and the feedback factor (β) are small, the loop gain is much smaller than one and no stability issue arises
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