Evaluation of Discrete-Time Wideband Receivers for NB-IoT

Sammanfattning: A receiver that covers several RF bands requires multiple front-end filters which increases the cost in terms of components and/or board/silicon area. Front-end filters assist a receiver to withstand interference at multiples of its down-conversion frequency. Analog discrete-time filters have gained a lot of traction lately, mainly due to their promising architecture, achieving baseband filtering, image and harmonic rejection within the same circuit, allowing a fully integration on-chip. These filters will also scale well with further process shrinking as only switches, capacitors and transconductors are required. The evaluation is performed with a standard 40 nm CMOS technology. This thesis aims to focus on those details that previous papers did not describe in detail, such as different topologies of switches and transconductors, mismatches, non-ideal clock sources, capacitive ratios, intermediate frequency, sample rate, common-mode, noise, on-resistance of switches, power consumption, folding, and simulation aspects with Spectre. To understand these filters a dedicated theory chapter is included, starting from a simple first-order low-pass filter up to the complex M/2M band-pass filter which uses M signals and 2M clock phases. All of the above is applied onto a Narrowband Internet of Things (NB-IoT) receiver, as specified in 3GPP release 15. However, a final receiver is not built, only a theoretical one on paper. Discrete-time filters are not suitable for NB-IoT, primarily due to the low requirement on bandwidth (180KHz), pointing towards a low baseband frequency, which is the opposite of what these filters are suitable for. A high sample rate is required to not degrade the systems performance from folding issues, causing high power consumption. The theoretical receiver is derived to handle all test cases and RF bands, as specified from 3GPP release 15. However, it was not possible to implement a receiver without any front-end filter due to the lack of attenuation of harmonic content over all RF bands. To reduce the power consumption a second-order anti-alias filter was required to reduce the sample rate. The Power consumption was 6.65 mW with a supply voltage of 1.2 V , excluding LNA, mixer, clock dividers and ADC.