All-digital Techniques Research Articles

Power‐efficient aliasing‐free PWM transmitter

Linearity and efficiency are important parameters in determining the performance of any wireless transmitter. Pulse-width modulation (PWM) based transmitters offer high efficiency but suffer from low linearity due to image and aliasing distortions. Although the problem of linearity can be addressed by using an aliasing-free PWM (AF-PWM), these transmitters have a lower efficiency as they can only use linear power amplifiers (PAs). Moreover, an all-digital implementation of such transmitters is not possible. The aliasing-compensated PWM transmitter (AC-PWMT) has a higher efficiency due to the use of switch-mode PAs (SMPAs) but uses outphasing to eliminate image and aliasing distortions and requires a larger silicon area. In this study, the authors propose a novel transmitter that eliminates both aliasing and image distortions while using a single SMPA. The transmitter can be implemented using all-digital techniques and achieves a higher efficiency as compared to both AF-PWM and AC-PWM based transmitters. Measurement results show an improvement of 11.3, 7.2, and 4.3 dBc in the ACLR as compared to the carrier-based PWM transmitter (C-PWMT), AF-PWMT, and AC-PWMT, respectively. The efficiency of the proposed transmitter is similar to that of C-PWMT, which is an improvement of 5% over AF-PWMT.

An All-Digital PLL Proposal using Gain Control Technique

Time-to-digital converter (TDC) has been the main technique used in all-digital phase-locked loops (ADPLL). However, this approach has several design issues, and the solutions to resolve them always increase the complexity of the system. In this paper, an alternative method for handle the frequency error detection using a type II ADPLL architecture is presented. The proposed technique does not perform direct conversion from time to digital, but employs the discrete-time processing of compared signals from phase error detection. This architecture has the advantage of scalability and integration of all-digital techniques and has less complexity than conventional ADPLLs. The derivation of equations for the proposed architecture and its noise analysis is provided. The results are validated through system level simulations using macro-models of the devices. The result of the transient simulation shows the theoretical predictions about the trajectory of output frequency.

State-of-the-Art and Future Directions of High-Performance All-Digital Frequency Synthesis in Nanometer CMOS

The past several years have successfully brought all-digital techniques to the RF frequency synthesis, which could arguably be considered one of the last strong bastions of the traditionally-analog design approaches. With their high sensitivity and high dynamic range requirements, the RF circuits have long had a good excuse to avoid any possible source of digital switching activity. With the constant scaling of CMOS feature size and the merciless push for integration, the existence of almost free and powerful digital logic could not go unnoticed. Hence, the environment was ripe to transform the RF functions into digital realizations, as well as to apply digital assistance to help with the performance of RF circuits. This paper revisits the digitization journey of the traditional charge-pump PLL that has resulted in an all-digital frequency synthesizer with the best-in-class RF performance while occupying only a fraction of the silicon area and consuming a fraction of the power. The paper also offers a few novel techniques to further improve area, current consumption, testability, and reliability of frequency synthesizers.

All-digital techniques for the optical broadband ISDN

Advances in technology have brought down the cost of deployment for fibre-based communications systems. The extension of fibre-based systems directly into businesses and residences will have a major impact on the development of the integrated service digital network (isdn), ushering in what is commonly referred to as broadband isdn (bisdn). bisdn can support a wide variety of services over high-bandwidth digital interfaces ranging from very low bit-rate telementry through full-motion highdefinition video. Bellcore has been investigating two types of switching techniques for use in the bisdn : space division circuit switching and high-speed packet switching. Interest in the design of high-speed packet switches is now receiving greater emphasis because of the selection of asynchronous transfer mode (atm) as the predominant switching and multiplexing technique for bisdn. Both types of switching fabrics can be dimensioned to operate efficiently over the proposed sonet transmission system. This paper focuses on the atm hardware for a second generation prototype of a local access bisdn that is being constructed to more fully understand the implications and trade-offs involved in the design of bisdn systems.

Comparative study of optical–digital vs all-digital techniques in textural pattern recognition

In this study we examine the application of both optical-digital and all-digital techniques in textural pattern recognition and make a comparison of the two approaches. The optical-digital scheme makes use of an optical-digital computer to generate textural measurements based on the 2-D irradiance spectrum. The all-digital scheme produces measurements based on gray-tone spatial-dependence matrices. In both cases two feature extraction algorithms were employed: the Hotelling trace method and the Foley-Sammon discriminant vector analysis. Classification was accomplished using the k-nearest neighbor decision rule. The performance of these techniques was evaluated in an experiment involving the classification of four texture patterns. The results show that, for the textures chosen, both approaches give high classification accuracy with the optical-digital method performing somewhat better.

Simulating a jet gas turbine with an analog computer

In the past several years heavy emphasis has been placed on all-digital or hybrid simulation techniques in the analy sis of dynamic systems. To some the unmodified analog computer might seem as anachronistic as the narrow-gauge steam locomotive. Often, however, the demon Economics steps in; at this time the analog computer presents a most satisfactory compromise between accuracy, flexibility and cost. This article, Simulating a jet gas turbine with an analog computer, is a "case history" of such a dynamic system study. The prospect of an undetermined number of explo ratory runs, coupled with a limited foreknowledge of the system components, made the use of the analog computer (an EAI 31-R) attractive. With Battelle's current open-shop policy on analog computer use, the computer became, in effect, an extension of the engineer's slide rule. In spite of being Little Orphan Analog in a digital world, the machine performed admirably!