A one-path subsampling quadrature receiver based on a ΣΔ modulator with distributed resonators
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This article presents experimental results of a quadrature bandpass sigma–delta (ΣΔ) modulator based on distributed resonators. The modulator employs transmission lines and transconductors as main components and does not require switches in the loop filter as in the case of switched-capacitor (discrete-time) filters. In addition, the proposed complex modulator does not require a quadrature mixer in the receiver. As main feature, the modulator architecture introduces an innovative way to produce the I and Q outputs that is immune to path mismatch due to the sharing of all the analog circuitry for both paths. The one-bit second-order modulator ADC is able to convert IF signals at fs/2 and 3fs/2 (fs = 50 MHz), achieving an ENOB = 10 bits within a 1 MHz signal bandwidth. Therefore the modulator may be feasible for the typical IF frequencies used in cellular base stations. Furthermore, it provides an image rejection grater than 70 dB. The 0.35 μm BiCMOS chip consumes 28 mW at 3.3 V supply voltage.
KeywordsAnalog-to-digital conversion Sigma–delta modulation Quadrature modulator Transmission-line (TL) resonators
This work has been sponsored by project TEC2007-67460-C03-03 of the Commission of Science and Technology (CICYT) (Spain) and CCG07-UC3M/TIC-3151 of the CAM (Spain).
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