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Bandpass Delta-Sigma Modulator and Down-Converter without Resonators

IP.com Disclosure Number: IPCOM000013413D
Original Publication Date: 2002-Jul-01
Included in the Prior Art Database: 2003-Jun-18

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Continuous-Time Bandpass Delta-Sigma Modulator is a solution for high-speed, high-resolution A/D (Analog to Digital) converters. In most of the applications the bandpass signal is sampled and then down converted digitally to baseband. The Delta-Sigma Modulator in this case is called Bandpass Delta-Sigma Modulator and the way to implement such modulator is to use resonators [1]. The accuracy of the resonators is very important factor and such accurate resonators are very hard to implement. In this invention I suggest a combined down converter and delta-sigma modulator which doesn’t include resonators. The invention is a different architecture for combined Bandpass Delta-Sigma modulator and down converter. A block diagram of the architecture is followed: The input signal is pass band signal, that means limited bandwidth signal (s(t)) modulated by sine wave: In the first stage of the Demodulator, the input is multiplied by a rectangular pulse (+1 and -1 of 50% duty cycle). The rate of this pulse is f, where: Where B (in Hz) is a number which is greater than the bandwidth of s(t ). The output of the multiplier includes another bandpass signal where: and n2(t) includes harmonies of the signal, generated by multiplying with rectangular pulse. The harmonies has higher frequencies then f2. This signal is the input to the lowpass Delta-Sigma modulator. The output of the lowpass Delta-Sigma modulator is a digital sequence which includes the wanted signal (s(t)*cos(2pf2t)), the unwanted harmonies, and correlated noise generated by any Delta-Sigma modulator. This noise component, is filtered by the Delta-Sigma filters, which are part of any Delta-sigma modulator.