A 0.65 V 4 dB NF 2.4 GHz Sub-Passive RF Down-Converter With Trans-Frequency Current-Reusing Scheme Achieving Low Flicker Noise and High Linearity

In this article, a 2.4 GHz low-power sub-passive radio frequency (RF) down-converter that employs trans-frequency current-reusing technique is proposed. Part of the RF trans-conductance ( <tex-math notation="LaTeX">gₘ</tex-math> ) stage is reused as the bias current source of the trans-impedance amplifier (TIA) to realize trans-frequency current reusing, thereby saving 30% power consumption of the sub-passive down-converter. Compared with a conventional passive down-converter where the flicker noise from the TIA's bias current source is fully fed into the intermediate frequency (IF) output terminal, the flicker noise originating from the TIA's current source supplied by the RF <tex-math notation="LaTeX">gₘ</tex-math> stage is up-converted and filtered out. The flicker noise corner frequency is cut down to 20 KHz, making it possible to apply zero-IF receiver for narrow-band communications. The linearity is also improved by sufficiently cancelling third-order transconductance from PMOS and NMOS <tex-math notation="LaTeX">gₘ</tex-math> transistors across a wide input swing range, which is contributed by their asymmetrical bias current in the low-noise transconductance amplifier (LNTA). Fabricated in TSMC 40 nm RF CMOS process, the prototype occupies a die area of 0.27mm <tex-math notation="LaTeX">²</tex-math> . Operating at 2.4 GHz, the sub-passive RF down-converter achieves a measured conversion gain (CG) of 56 dB and a noise figure (NF) of 4 dB, while implementing a 23 dBm output third-order intercept point (OIP3) with 0.8 mW power consumption at a supply voltage of 0.65V.