A Sawtooth Relaxation ICO based 1-1 MASH ADC

A novel way of extracting quantization error in a Current-Controlled Oscillator (ICO) based open loop multi-stage noise shaping (MASH) Delta-Sigma ADC is proposed. The ICO is designed as a sawtooth generator with output level sensing to extract the quantization error as an analog voltage at the sampling instance. This voltage is processed by similar successive stages to reduce the effective quantization error, similar to the MASH topology. This open loop architecture alleviates the concerns of instability due to excess loop delays akin to higher order sigma delta ADCs and allows to achieve improved resolution without the need of highly linear Digital-to-Analog Converters (DACs). Using identical ICOs with simple phase counters and filtering techniques in digital domain, a higher resolution ADC with a second order noise shaping is conceptually realized. The proposed architecture is also insensitive to ICO mismatches.