An A/D converter based on pulse width modulation and the walsh-hadamard transform

This paper shows the architecture of an analog to digital converter aimed to very low voltage technologies. Its operating principle is based on an asynchronous analog pulse width modulator (PWM). A PWM binary signal is transformed to the Walsh-Hadamard domain using logic gates and passive filters only. The Walsh transform coefficients are sampled at a low rate and quantized, forming the digital output. Most of the signal processing of this converter is done with digital logic and passive circuits, which enables a low power and low voltage operation.