Design of RF front-end circuit blocks for low-power applications

Abstract

This report aims to provide a comprehensive review as well as the design of the various high frequency circuits found in almost all the transceivers in the market today. Wireless communication has become a natural part of everyone’s life, its presence can be seen all around. The high frequency circuits include low noise amplifiers (LNA), mixers and pre-amplifiers (PA).

In every receiver system, the LNA is the first block placed in the receive path, therefore its performance is critical in the exact operation of the receiver. The primary role of the LNA is to amplify the weak Radio Frequency (RF) signals, having suffered propagation loss after transmission through a medium, while minimizing its noise contribution to the overall system. Gain and noise figure are well correlated, higher gain would produce lower noise figure. Correspondingly, to achieve high gain, power consumption is increased. For mobile wireless devices, this would cause a severe drain on battery life. Therefore a novel LNA, operating in the subthreshold region is introduced to alleviate this issue.

Most modulators and demodulators are not able to achieve the high sampling rate required at RF frequencies. Thus, mixers circuits are needed to convert the modulated signals with a carrier frequency to the desired frequency. In the case of a transmitter system, the mixer is used to up convert the modulated immediate frequency (IF) into RF signal for transmission. Due to modulation scheme adopted and high bandwidth requirements of certain wireless applications, a wideband and high linearity mixer is needed to fulfill these functions.

Lastly, a transmitter would need to drive an off chip load, usually in the form of an antenna. A PA is usually employed to accomplish the task. By incorporating a power amplifier on-chip several considerations need to be addressed, a power amplifier have high gain resulting in a huge signal swings. These signals tend to find their way to other frequency sensitive circuits such as oscillators, through certain feedback paths or substrate coupling. This effect is normally known as ‘injection pulling’. Proper shielding or isolation is therefore crucial for the proper operation of the entire transceiver system.