Design of wideband noise-cancelling low-noise amplifiers

Abstract

In recent decades, the demands for radio frequency (RF) front-ends supporting a multiplicity of bands and standards have driven both research and industry toward the design of broadband low-noise amplifier (LNA), which is promising for software-defined radios (SDR) and broadband communications. As the forefront of the wideband receivers, an LNA is supposed to provide low noise figure (NF), adequate gain, good impedance matching and linearity with small area and low power. To effectively suppress the noise of the input transistor, the noise-cancelling (NC) technique is widely used in wideband LNAs. By adding an auxiliary amplifier to cancel the noise contribution of the main amplifier, low NF is achieved at the cost of power consumption. The objective of this research is to explore the NC technique and improve the overall performance of the LNA with a good trade-off among gain, NF, bandwidth, power consumption and die area. In this thesis, three NC CG-CS LNAs are presented for broadband applications. Firstly, a wideband NC CG-CS LNA with active feedforward for simultaneous current and noise reduction is presented. By employing an active feedforward stage in the main path, the current dissipation as well as the thermal noise is effectively suppressed, while the noise and distortion cancellation properties of CG-CS topology are preserved. Moreover, no extra noise is introduced by the gm-boost amplifier since it follows the same NC procedure as the main amplifier and its noise can be fully cancelled at the output theoretically. To further extend the bandwidth to 11 GHz, two on-chip inductors are added in the proposed LNA, where one inductor is employed at the input to resonate with the input parasitic capacitance while the other is inserted at the output for series peaking. Secondly, based on the firstly proposed LNA, an NC CG-CS LNA with a passive network is presented to improve the gain and noise performance simultaneously. By adding an additional passive network at the output, the noise contribution of the current-bleeding circuit can be fully removed. Moreover, the passive network also works as shunt peaking for bandwidth extension. Thanks to the combination of the shunt and series peaking, the proposed work achieves larger gain than that of the conventional work. Thirdly, a positive-feedback-based NC technique is presented to reduce the NF and power consumption simultaneously. In the traditional NC LNAs, with the noise contribution of the main amplifier cancelled, the noise contribution of the auxiliary amplifier dominates the NF of the LNA. However, the noise factor contributed by the auxiliary amplifier is inversely proportional to the transconductance of the auxiliary amplifier, and hence, the noise contribution of the auxiliary amplifier can only be reduced at the cost of power consumption. The proposed work is the first LNA, where the noise factor contributed by the auxiliary amplifier is proportional to the transconductance of the auxiliary amplifier, allowing for simultaneous current and noise reduction. All these presented LNAs are verified through calculations, simulations as well as silicon measurements.