A/D conversion using an Asynchronous Delta-Sigma Modulator and a time-to-digital converter

An analog to digital conversion scheme based on an Asynchronous ΔΣ Modulator is presented. It uses a Time-to-Digital converter to convert the continuous-time square wave signal produced by the Asynchronous ΔΣ Modulator to a time-quantized digital signal. The original input signal is then recovered by applying a digital demodulation algorithm derived from general duty-cycle modulation theory. This technique shifts the complexity towards the digital domain and is therefore especially suited for ultra-low voltage technologies beyond 90 nm. Simulations show 13 bit accuracy for Bluetooth baseband 500 kHz with a first-order ΔΣ modulator and a Time-to-Digital Converter with 10 ps resolution running at 12 MHz. Using a second-order feedback system to shape the quantization noise of the Time-to-Digital converter, the bandwidth can be increased to 12 MHz with 12 bit accuracy, suitable for video applications.