Sigma-Delta PWM for class-D audio and other Sigma-delta tricks
The Balloon (Holiday Special)
Spoiler Alert! It is better if you do not look at this before the lecture.
The target is to build a driver for the TAS5602 by Texas Instruments. This chip expects a pulse-width modulated signal with at most 400kHz base frequency. We have an FPGA with a maximum clock frequency of 50 MHz. So what we need to do is to drive the digital PWM generator with a sigma-delta bitstream.
How to proceed:
- Understand the 8-bit (256-step) pulse width modulator (pwmstage.mdl, go_pwmstage_00.m)
- Replace the comparator in the sigma-delta converter by a 256-step quantizer (example: sd2multibit.mdl, go_sd2multibit_00.m)
- Combine both and optimize SNR
- If you want, feed audio through your solution.
Learning Targets formulated in 2009
- How a MASH converter works in principle
- How a low-distortion converter works (signal bypassing the loop filter)
- How a converter with noise coupling works
- PWM stage driven by a sigma-delta bitstream
(compiled by Hanspeter Schmid)