An Active Feedback Interference Cancellation Technique for Blocker Filtering in RF Receiver Front-Ends

Abstract

A feedback interference cancellation circuit is presented that uses a control loop to reject blockers in wireless receivers. The concept is based on a feedback translational loop which subtracts a blocker replica from the original blocker signal. In contrast to feedforward methods loop selectivity does not depend on exact gain matching of two paths but on the open loop gain which is easier to adjust. The concept is described including the theoretical derivations of the transfer function and stability. Nonidealities like I/Q mismatch and noise mechanisms are discussed. Finally, measurements from a prototype chip in 65-nm CMOS are presented showing the feasibility of active feedback cancellation. In a desensitization scenario, gain drops by more than 12 dB for a 15 dBm blocker at 20 MHz offset without feedback interference cancellation while a gain degradation of merely 3 dB is measured with feedback interference cancellation enabled.

Frequency translation loops for RF filtering : theory and design

“…Better or comparable wideband IIP3 of > +12dBm is measured at 2.5 to 13 times lower frequency offset (60MHz) compared to most reported values [24,46]. Moreover, this design significantly outperforms previously reported feedback-based receivers [43,46] in terms of gain, frequency range, stop-band rejection and wideband IIP3 while maintaining a competitive performance for other receiver parameters. …”

“…Several other works have used frequency translation loops, mostly with passive mixers [43][44][45], although active mixers have also been used [46]. In [43] and [46] filtering is carried out via a separate negative feedback loop (i.e.…”

“…However, despite their wide use as discussed above, no similarly detailed analysis is available for frequency translation loops with passive mixers. Rather, only basic system level analysis is available, mainly to provide a qualitative description for the operation of the loop [43,44,48], or investigate general receiver non-idealities like I/Q mismatch [49].…”

Interference cancellation for the coexistence of 5.8 GHz DSRC and 5.9 GHz ETSI ITS

“…Analog cancellation [5] is based on the feed-forward control of the interference signal (aggressor), whose topology is schematically depicted in Fig. 1, [6], [7], [8].…”

Active feedback receiver with integrated tunable RF channel selectivity, distortion cancelling, 48dB stopband rejection and >+12dBm wideband IIP3, occupying <0.06mm² in 65nm CMOS

“…Since the feedback loop sinks current, filter rejection at the RF side is not limited by the resistance of the down-conversion mixer switches. As opposed to other feedback-based receivers [4,5], the proposed architecture incorporates the receiver's downconversion path within the loop to provide an IF output instead of having a separate rejection loop after the LNA with an RF output that needs further down-conversion.The channel bandwidth is now determined by the corner frequency of the HPF (ωHPF) divided by 1+TO, where TO is the loop gain ( Fig. 9.3.1-bottom).…”