A subsampling delta-sigma modulator for global navigation satellite systems

Ucar, A. 2010. A subsampling delta-sigma modulator for global navigation satellite systems. PhD thesis University of Westminster School of Electronics and Computer Science

TitleA subsampling delta-sigma modulator for global navigation satellite systems
TypePhD thesis
AuthorsUcar, A.
Abstract

Next-generation Global Navigation Satellite Systems (GNSS) receivers should

be capable of processing multi-frequency signals in order to provide better

positioning accuracy and signal availability to end-user. Nevertheless, the

realization of such receivers with conventional receiver architectures leads to

power-hungry devices and hinders monolithic integration of the receiver.

Multi–frequency receivers can be realized with lower power and cost by

performing sub-Nyquist sampling (subsampling) at Radio Frequency (RF). In

practice, the use of subsampling receivers has been limited due to their poor

noise performance. This is particularly a concern in applications of Code

Division Multiple Access (CDMA) such as GNSS since subsampling may

saturate the Analog-to-Digital Converter (ADC) as the thermal noise floor is

above the signals of interest. Continuous-Time (CT) Delta-Sigma (ΔΣ)

modulation is an attractive candidate for subsampling Analog-to-Digital (A/D)

conversion as it provides noise-shaping and inherent Anti-Alias (AA) filtering.

However, the attenuation of the RF alias in the feedback path of the

modulator and the reduction of the effective Quality (Q-factor) of the loop

filter prevent conventional CT-ΔΣ modulators to be utilized in subsampling

receivers. This thesis proposes a novel CT-ΔΣ modulator at both the system

and the circuit level that is capable of compensating for the effects of

subsampling. These are achieved by modifying the feedback path of the

conventional modulator architecture to accommodate for the RF alias and by

enhancing the Q-factor of the loop filter. The proposed CT-ΔΣ has significant

improvements over previously published subsampling modulators as it

provides jitter and alias suppression and excess loop delay compensation to

improve the dynamic range, thus enabling the modulator to be utilized in

subsampling receivers when a relatively low sampling rate is desired. Based on

the novel CT-ΔΣ modulator, this thesis also proposes a subsampling receiver

architecture for multi-constellation GNSS applications. Simulations results

indicate that the proposed receiver architecture can successfully acquire and

track the civilian radionavigation signals with a high performance.

YearNov 2010
FileAlper_UCAR.pdf
Publication dates
CompletedNov 2010

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Permalink - https://westminsterresearch.westminster.ac.uk/item/9018w/a-subsampling-delta-sigma-modulator-for-global-navigation-satellite-systems


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