A Δ-Σ Digital Amplitude Modulation System
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Amplitude modulation (AM) is a very well understood and developed signal processing technique. AM was the earliest modulation method used to transmit voice by radio. It was developed during the first quarter of the twentieth century. There are numerous publications on this subject, including scientific papers, books, patents, and IC data sheets. Basic principles of its operation can be found on the Internet or in any communications textbook [1, 2]. In addition to the classic analog amplitude modulation, there are several digital amplitude modulation techniques. The oldest one is on-off keying (OOK) which dates to the time of Morse telegraph transmission. Still today, many wireless sensors working at 433 MHz use OOK. Over the years various modulation techniques have been developed such as pulse amplitude modulation (PAM), m-ary PAM, amplitude shift keying (ASK) , etc. Use of the Δ-Σ modulation for RF applications is elaborated in reference . It is worth mentioning that a Δ-Σ modulation is frequently referred to as a pulse density modulation [3, 4] because the density of pulses of a Δ-Σ pulse stream is proportional to the amplitude of an input signal. The proposed UC Berkeley RF pulse density system generates an amplitude-modulated waveform with up to 20 MHz envelope bandwidth and demonstrates the validity of this approach for modern communication standards .
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