Analysis of Timing Error Aperture Jitter on the Performance of Sigma Delta ADC for Software Radio Mobile Receivers

Jitter is the limiting effect for high speed analog-to digital converters with high resolution and wide digitization bandwidth, which are required in receivers in order to support high data rates. The rapid development of digital wireless system has led to a need of high resolution and high speed analog to digital converter. The proper selection of data converters, both analog to digital converters and digital to analog converters (DACs) is one of the most challenging steps in designing software radio. The performance of a data converter is dependent upon the accuracy and stability of the clock supplied to the circuits. When data converter employ a high sampling rate, clocking issues become magnified and significant distortion can be result. This paper describes the effect of aperture jitter on the performance of sigma delta ADC and present analytical evaluation of the performance and mean error power spectrum due to aperture jitter application has favored the use of oversampling delta sigma ADC (analog-to-digital converters) due to their better speed-accuracy tradeoff. Delta-sigma modulator is one of the key building blocks, which can be implemented using DT (discrete-time) and CT (continuous-time) techniques. Compared to their DT counterparts, CT delta-sigma modulators have recently attracted more and more attentions due to their advantages in terms of high speed, low power, low noise and intrinsic anti-aliasing capability. In this paper, we concentrate on the discrete implementation. Section 2 presents an aperture jitter effect in SDM in terms of SNR. In the last few years different authors derived formulas to quantify the SNR limiting effect of jitter in ADCs. While Walden used a worst case approach, Kobayashi presented an exact formula which allows calculating the SNR in the presence of an aperture jitter.

1. Introduction

A software radio (also called a “flexible architecture radio”) is one of the most important emerging technologies for the future of wireless communication services because of traditionally analog functions of a radio receiver will be replaced with software or digital hardware [1]. Software radio architecture are shown in Figure(1). Modern mobile communication receivers require high speed analog-to-digital converters which provide a high resolution for a wide digitization bandwidth. In the past years, the demand for high speed and low power wire-line and wireless an application has favored the use of oversampling Delta-Sigma ADC (Analog-to-Digital Converters) due to their better Speed-accuracy tradeoff [5]. Delta-Sigma modulator is one of the key building blocks, which can be implemented using DT (Discrete-Time) and CT (Continuous-Time) techniques. Compared to their DT counterparts, CT Delta-Sigma modulators have recently attracted more and more attentions due to their advantages in terms of high speed, low power, low noise and intrinsic anti-aliasing capability [5]. In this paper, we concentrate on the discrete implementation. Section 2 presents an aperture jitter effect in SDM in terms of SNR. In the last few years different authors derived formulas to quantify the SNR limiting effect of jitter in ADCs. While Walden used a worst case approach [9], Kobayashi presented an exact formula which allows calculating the SNR in the presence of an aperture jitter [10]. Figure 1. Software Radio Architecture