Agenda
MSc ME Thesis Presentation
- Thursday, 31 October 2019
- 15:00-15:30
- Building 34, Lecture Hall E (Robert Hooke)
A Dynamic Zoom ADC for Audio Applications
Efraïm Eland
Audio ADCs used in high-fidelity portable audio and IoT are not only required to have high linearity and dynamic range (DR) but are also expected to be very energy efficient and occupy minimum silicon area. Zoom-ADCs combine a coarse asynchronous SAR with a fine Delta-Sigma Modulator (∆ΣM) to satisfy these requirements. Existing zoom ADC architectures are limited in terms of SQNR due to the need for the fine ADC to have some over-ranging. That, together with the leakage of the SAR ADC’s quantization noise, “fuzz,” into the audio band, puts a lower limit on the sampling frequency.
This thesis describes the design of a zoom-ADC for an audio bandwidth of 20kHz. Using a 4-level quantizer, instead of a conventional 1b quantizer, mitigates the adverse effects of over-ranging, making it possible to keep a very low sampling frequency. On top of that, it makes use of a simple, low power analog “fuzz” cancellation scheme to prevent the SAR quantization noise from leaking into the audio band.
The chip has been prototyped in a standard 160nm CMOS technology and consumes 339μW with 107.7dB DR and 105dB SNDR. Compared to state-of-the-art ADCs with a similar bandwidth, this work achieves a 2x lower OSR (fs = 2.5MHz), significantly improving the energy efficiency and achieving a Schreier FoM of 185.4dB.