The frequency spectrum of pulse width modulated signals
Signal Processing - Special section: Security of data hiding technologies
An analog squaring technique based on asynchronous sigma-delta modulation
IEEE Transactions on Circuits and Systems II: Express Briefs
Delta-sigma A/D conversion via time-mode signal processing
IEEE Transactions on Circuits and Systems Part I: Regular Papers
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This paper describes a delay-and-addition cell that enables direct signal processing of pulse with modulation (PWM) encoded signals. The cell can be considered functionally equivalent to a switched capacitor integrator. However, both its input and output are synchronous PWM signals. As a difference to a switched capacitor integrator, the circuit does not require operational amplifiers and is composed of passive RC circuits, switches, comparators and digital logic. Circuit implementation non idealities such as offset and propagation delays have also been analyzed. The main advantage of this circuit is the possibility to operate at a low voltage. The paper shows measurements of a demonstration circuit implementing a first order filter. As an application example, the filter is used to attenuate the quantization noise of a sigma-delta signal, delivering a continuously varying PWM waveform from a synchronous bitstream.