Audio Telecom ADC Featuring Click-Free Gain Control Technique, Dithering Insertion, and Idle Tone Shifting

Applying pulsewidth modulation (PWM) to control the gain in audio codecs for mobile applications leads to several advantages, such as the smooth control of tuning parameters, smaller silicon area, and lower power consumption, as compared with other tuning techniques using programmable gain amplifiers and zero crossing detectors. The PWM has to be embedded into the main signal path, preferably in a closed-loop control scheme, in order to exploit its benefits. However, the insertion of dithering and offset controls in a gain setting loop poses the problem of controlling their effects in all gain conditions. This paper reports a novel technique aimed at solving the associated issues and limitations, and provides the experimental proof of the concept through the implementation of a test-chip design on silicon. In particular, this paper reports the design and experimental results of a delta-sigma analog-to-digital converter featuring a click-free gain control technique, dithering insertion, and idle-tone shifting, which has been implemented in a 40-nm complementary metal-oxide-semiconductor technology for commercial telecom audio codec applications.