SAW-less analog front-end receivers for TDD and FDD

In cellular receivers, out-of-band blockers are generally managed by surface-acoustic-wave (SAW) filters between the antenna and the low-noise amplifier (LNA). For Time Division Duplexing (TDD), such as GSM, the SAW can be removed if the receiver can handle very large interferers (e.g. in GSM 0dBm 20 MHz away) [1]. Generally SAW filters also perform differential to single-ended (SE) conversion (balun). Once the SAW is removed an SE transceiver eliminates the external balun, reducing cost and attenuation. For the same sensitivity, a SAW-less SE transceiver can have a noise figure (NF) 2 to 3dB higher than a classical one. An SE LNA could be susceptable to couplings from supply and substrate, which are usually rejected through symmetry. Therefore it should become symmetric as closely as possible to the input pin. A SAW-less differential transceiver [2] can also be appealing if it has an NF close to that of classical transceivers. This is because it can have better sensitivity in TDD (a balun attenuates less than a SAW) and it can be very flexible, being usable for both FDD (where duplexers are differential) and TDD.