Frequency-translation techniques for interference-robust software-defined radio receivers

A Blocker-Tolerant, Noise-Cancelling Receiver Suitable for Wideband Wireless Applications

“…A number of innovative designs have shown that a wideband CMOS front-end can tolerate blockers as large as 0 dBm [6]- [13]. While different techniques are employed, all these circuits have two common features: they employ passive-mixers, and they suppress voltage gain at blocker frequencies.…”

“…In [18] and later in [11]- [13], the LNA is replaced with a linear transconductance, which drives a current mode passive mixer ( Fig. 5(a)).…”

“…In addition to their excellent linearity and low flicker noise [18], [21], [37], passive mixers can handle large downconversion currents [6]- [13], [22]- [25] and, therefore, it is the auxiliary transconductance cell that will ultimately limit the achievable large-signal linearity of the system. Importantly, unlike other receiver topologies, this transconductance does not need to provide impedance matching and, so, its design is greatly simplified.…”

“…Note that when the auxiliary path is powered down and noise cancelling is disabled, the receiver behaves like an equivalent mixer-first receiver and the noise factor is given by [31]: (13) If is small, matching requires that and the noise figure will be limited to 3 dB. Even if this is not the case and the up-converted TIA input impedance is used to provide matching, noise due to the baseband TIAs will contribute directly to the receiver's noise figure and flicker noise is likely to be significant.…”

“…But, as the authors of [3]- [5] themselves acknowledge, such designs are incapable of meeting the stringent blocker specifications demanded by cellular standards. More recently, recognizing the high linearity of passive-mixers, a number of "blocker-tolerant" CMOS receivers have been developed [6]- [13], but in each case linearity and wideband operation comes at the expense of noise figure. What is needed is a wideband blocker-tolerant receiver that exhibits a sufficiently low noise figure that it may be used in place of multiple narrowband low-noise front-ends. Within this context, we describe a new receiver architecture [14] that can tolerate large out-of-band blockers without relying on SAW pre-filters, and without sacrificing noise performance.…”