143 research outputs found
ADDA - A versatile development platform for AD-and DA- converters
No full textADDA is a versatile development platform for AD-and DA- converters. It contains performance analysis algorithms for converters enabling the user to characterise converters and create data-sheets. The converters characterised are either simulated or real products. Currently characterisation and modelling of Nyquist converters are included with delta-sigma converters to follow in a future release. The platform, written in C-language, is free software released with the Gnu General Public License (GPL) and is freely available for all parties interested to contribute with models, analysis methods or measurement setups. New models of converters are easily included in the platform following included templates and the instructions in the README.</p
NETTAN -A tool for Analysis and Iterative Design of Analog-, Digital-and Switched-Capacitor Filters
No full textNETTAN is a versatile development platform for filter analysis and design. It contains analysis algorithms for filters enabling the user to characterise a given filter or iteratively synthesise a filter for a target specification by optimisation. Filters included are passive RLC-, active RC-, digital and Switched-Capacitor filters. The platform, written in the Fortran language, is free software released with the Gnu General Public License (GPL) version 3 or later. It is especially useful for all parties interested to contribute with new analysis and/or synthesis methods. Other uses are for educational purposes, and NETTAN can be included in any graduate course having filters as one of the course subjects. Usage of the tool is simplified by the users manual and an on-line help.</p
Harhatoistojen karaktorisointi ja minimointi Delta-Sigma muuntimissa
No full textAbstractOversampling data converters based on Delta-Sigma modulation are a popular solution for modern high-resolution applications. In the design of digital-to-analog or analog-to-digital Delta-sigma converters there are common obstacles due to the difficulties on predicting and verifying their performance. Being a highly nonlinear system, a Delta-Sigma modulator’s (DSM) quantization noise and therefore the spurious tones are difficult to analyze and predict. Multi-bit DACs can be used to improve the performance and linearize the behavior of DSMs. However, this will give rise to the need for linearizing the multi-bit DAC. A popular DAC linearization method, data weighted averaging (DWA) shapes the DAC mismatch noise spectrum. There are many variants of DWA, for low-pass and band-pass DSMs. This thesis proposes a generalization which integrates a few published variants into one, broader DWA scheme. The generalization enables expanding the tone-suppression studies into a larger concept. The performance of one- or multibit DSMs is usually verified by simulations. This thesis proposes a simulation-based qualification (characterization) method that can be used to repeatedly verify and compare the performance of multibit DSM with a DAC mismatch shaping or scrambling scheme. The last contribution of this thesis is a very simple model for tonal behavior. The model enables accurate prediction of spurious tones from both DSMs and DWA-DACs. The model emulates the tone behavior by its true birth-mechanism: frequency modulation. The proposed prediction model for tone-behavior can be used for developing new tone-cancelation methods. Based on the model, a DWA linearization method is also proposed. TiivistelmäDelta-Sigma modulaatio on suosituin tekniikka ylinäytteistävissä datan muuntimissa. Riippumatta toteutustarkoituksesta (analogia-digitaali- tai digitaali-analogia-muunnos), Delta-Sigma (DS) modulaatiossa on yleisesti tunnettuja käyttäytymisen ennustamiseen liittyviä ongelmia. Nämä ongelmat ovat peräisin modulaattorin luontaisesta epälineaarisuudesta: DS-muunnin on nimittäin vahvasti epälineaarinen takaisinkytketty systeemi, jonka harhatoistojen ennustaminen ja analysointi on erittäin hankalaa. Yksibittisestä monibittiseen DS-muuntimeen siirryttäessä muuntimen suorituskyky paranee, ja muuntimen kohinakäyttäytyminen on lineaarisempaa. Tämä kuitenkin kostautuu tarpeena linearisoida DS-muuntimen digitaali-analogia (D/A) muunnin. Tällä hetkellä tunnetuin linearisointimenetelmä on nimeltään DWA (data weighted averaging) algoritmi. Tässä työssä DWA:lle ja sen lukuisille varianteille esitellään eräänlainen yleistys, jonka avulla algoritmia voidaan soveltaa sekä alipäästö- että kaistanpäästö-DS-muuntimelle. Kuten tunnettua, DS-modulaattorin analyyttinen tarkastelu on raskasta. Yksi- ja monibittisten DS-muuntimien suunnitellun käyttäytymisen varmistaminen tapahtuukin yleensä simulointien avulla. Työssä esitetään simulointiperiaate, jolla voidaan kvalifioida (karakterisoida) monibittinen DS-muunnin. Tarkemmin, kvalifioinnin kohteena on DWA:n kaltaiset D/A -muuntimien linearisointimentelmät. Kyseessä on pyrkimys ennen kaikkea toistettavaan menetelmään, jolla eri menetelmiä voidaan verrata nopeasti ja luotettavasti. Tämän väitöstyön viimeinen kontribuutio on matemaattinen malli harhatoistojen syntymekanismille. Mallilla sekä DS-muunnoksen että DWA-D/A -muunnokseen liittyvät harhatoistot voidaan ennustaa tarkasti. Harhatoistot mallinnetaan yksinkertaisella havaintoihin perustuvalla FM-modulaatiokaavalla. Syntymekanismin mallinnus mahdollistaa DS-muuntimien ennustettavuuden ja täten auttaa harhatoiston kumoamismenetelmien kehittämistä. Työssä esitetään yksi matemaattisen mallin avulla kehitetty DWA-D/A -muunnoksen linearisointimenetelmä. Academic dissertation to be presented with the assent of the Faculty of Technology of the University of Oulu for public defence in OP-sali (Auditorium L10), Linnanmaa, on 17 February 2012, at 12 noonAbstract
Oversampling data converters based on Delta-Sigma modulation are a popular solution for modern high-resolution applications. In the design of digital-to-analog or analog-to-digital Delta-sigma converters there are common obstacles due to the difficulties on predicting and verifying their performance. Being a highly nonlinear system, a Delta-Sigma modulator’s (DSM) quantization noise and therefore the spurious tones are difficult to analyze and predict.
Multi-bit DACs can be used to improve the performance and linearize the behavior of DSMs. However, this will give rise to the need for linearizing the multi-bit DAC. A popular DAC linearization method, data weighted averaging (DWA) shapes the DAC mismatch noise spectrum. There are many variants of DWA, for low-pass and band-pass DSMs. This thesis proposes a generalization which integrates a few published variants into one, broader DWA scheme. The generalization enables expanding the tone-suppression studies into a larger concept.
The performance of one- or multibit DSMs is usually verified by simulations. This thesis proposes a simulation-based qualification (characterization) method that can be used to repeatedly verify and compare the performance of multibit DSM with a DAC mismatch shaping or scrambling scheme.
The last contribution of this thesis is a very simple model for tonal behavior. The model enables accurate prediction of spurious tones from both DSMs and DWA-DACs. The model emulates the tone behavior by its true birth-mechanism: frequency modulation. The proposed prediction model for tone-behavior can be used for developing new tone-cancelation methods. Based on the model, a DWA linearization method is also proposed.Tiivistelmä
Delta-Sigma modulaatio on suosituin tekniikka ylinäytteistävissä datan muuntimissa. Riippumatta toteutustarkoituksesta (analogia-digitaali- tai digitaali-analogia-muunnos), Delta-Sigma (DS) modulaatiossa on yleisesti tunnettuja käyttäytymisen ennustamiseen liittyviä ongelmia. Nämä ongelmat ovat peräisin modulaattorin luontaisesta epälineaarisuudesta: DS-muunnin on nimittäin vahvasti epälineaarinen takaisinkytketty systeemi, jonka harhatoistojen ennustaminen ja analysointi on erittäin hankalaa.
Yksibittisestä monibittiseen DS-muuntimeen siirryttäessä muuntimen suorituskyky paranee, ja muuntimen kohinakäyttäytyminen on lineaarisempaa. Tämä kuitenkin kostautuu tarpeena linearisoida DS-muuntimen digitaali-analogia (D/A) muunnin. Tällä hetkellä tunnetuin linearisointimenetelmä on nimeltään DWA (data weighted averaging) algoritmi. Tässä työssä DWA:lle ja sen lukuisille varianteille esitellään eräänlainen yleistys, jonka avulla algoritmia voidaan soveltaa sekä alipäästö- että kaistanpäästö-DS-muuntimelle.
Kuten tunnettua, DS-modulaattorin analyyttinen tarkastelu on raskasta. Yksi- ja monibittisten DS-muuntimien suunnitellun käyttäytymisen varmistaminen tapahtuukin yleensä simulointien avulla. Työssä esitetään simulointiperiaate, jolla voidaan kvalifioida (karakterisoida) monibittinen DS-muunnin. Tarkemmin, kvalifioinnin kohteena on DWA:n kaltaiset D/A -muuntimien linearisointimentelmät. Kyseessä on pyrkimys ennen kaikkea toistettavaan menetelmään, jolla eri menetelmiä voidaan verrata nopeasti ja luotettavasti.
Tämän väitöstyön viimeinen kontribuutio on matemaattinen malli harhatoistojen syntymekanismille. Mallilla sekä DS-muunnoksen että DWA-D/A -muunnokseen liittyvät harhatoistot voidaan ennustaa tarkasti. Harhatoistot mallinnetaan yksinkertaisella havaintoihin perustuvalla FM-modulaatiokaavalla. Syntymekanismin mallinnus mahdollistaa DS-muuntimien ennustettavuuden ja täten auttaa harhatoiston kumoamismenetelmien kehittämistä. Työssä esitetään yksi matemaattisen mallin avulla kehitetty DWA-D/A -muunnoksen linearisointimenetelmä
Jittered uniform sampling - examples
No full textIn many communication systems jitter is a problem causing performance degradation. The jitter is present in both analogue parts and in the sampling process. In this contribution examples of calculated and simulated spectra are shown for uncorrelated Uniform and uncorrelated and correlated Gaussian jitter distributions. Closed form expressions are also given for selected correlated noise cases. In two companion contributions, [1] random input signals and [21 deterministic input signals perturbed by jitter are analysed and the mathematical foundation to the examples given here are made. The analytical results show that the output signal spectrum consists of both discrete and continuous parts. For some applications, such as instruments for spectrum analysis, large jitter can be of great use utilizing the fact that discrete alias components can be completely removed with sufficiently large jitter.</p
Non-traditional architectures for AD- and DA-converters
No full textTraditional AD-converters of cyclic or pipeline type normally use algorithms that create offset binary output code. The input sample is converted starting with the most significant bit (MSB) and ends with the least significant bit (LSB), giving a total of N bits. In cyclic converters this is achieved by one processing element resolving a number of bits, M, with the residue voltage is scaled by M and fed back to the input in a recursive manner in a loop. For pipeline converters this loop is rolled out, using one processing element for each set of M bits and using N/M processing stages. Current popular state-of-the-art converter architectures use M=1 and M=1.5, with error correction for the 1.5 bit case. Cyclic converters are normally used for medium speed operation and can be designed for extremely small silicon area and power consumption, while pipeline converters can be very high speed at the cost of more area and power consumption. Nonidealities in the processing elements, such as capacitor mismatch, amplifier and comparator offsets, signal dependent and independent charge injection, finite OTA gain- and bandwidth and noise will induce errors in the residue voltages that eventually affect the accuracy of the converter limiting its resolution [1],[2]. The errors can be both random and systematic. Normally these errors are addressed by circuit level improvements meant to reduce their magnitude. Alternately, some of the errors can be mitigated at the block level, especially the systematic errors. The use of Gray coding [3] achieves a lower accumulation of errors that depends on the bits generated. The net effect of Gray coding is to introduce only a gain difference, compared to an ideal converter. Two other alternatives are to slightly modify the Binary output code, by alternating the residue error sign at each cycle [4],[5], or alternate the sign for the MSB residue voltage [4]],[6]. These modifications improve the performance by several bits compared to traditional Binary coded converters. These improvements are obtained at no extra hardware cost, since only complementary binary outputs are needed, which are already available for fully differential realizations. For DA-converters the concept of cyclic and pipelined converters can easily be obtained, by reversing the operations for the ADC algorithms. The resulting DACs start with the LSB and the conversion is completed when the MSB is processed, either in a cyclic manner or pipelined. The input signal can be Binary coded, alternate Binary coded or Gray coded [7]-[9]. Substantial performance improvements are achievable also for DACs at the block level by modifying the digital input code format in a similar manner as for ADCs. Traditional high-performance DACs are normally built as two-stage converters, using one coarse and one fine stage using combinations of R2R ladders and Binary weighted current sources. The outputs are for most designs a current. In order to achieve low thermal noise the terminating resistor is small, resulting in a large power consumption. The techniques described above allow one to use voltages as outputs, giving potential advantages in power consumption. This paper gives a brief overview of the alternate architectures for ADCs and DACs using simple algorithm modifications at the block level and the possible performance improvements are motivated and verified.</p
Impact of Channel Estimation Error on Performance of Adaptive MIMO Systems
No full textAdaptive modulation scheme has been widely used in multiple-input multiple-output (MIMO) systems to enhance the spectral efficiency while maintaining the bit-error-rate (BER) under a target level. In this work, we investigate the performance of adaptive modulation in the presence of imperfect channel estimation and the impact of estimation noise on the spectral efficiency. The closed-form expressions for the average spectral efficiency are derived. Two MIMO schemes are considered, i.e., orthogonal space-time block codes (OSTBC) and spatial multiplexing with zero-forcing receiver (SM-ZF), and a low complexity method to enable the transmitter to switch between OSTBC and SM-ZF is utilized to achieve higher spectral efficiency than adaptive OSTBC and adaptive SM-ZF.</p
Comparison of CP-OFDM and OFDM/OQAM in doubly dispersive channels
No full textIn this paper we compare the performance of cyclic prefix based OFDM (CP-OFDM) system and OFDM/offset QAM (OFDM/OQAM) system in doubly dispersive channels, by investigating the signal reconstruction perfectness, time and frequency dispersion robustness, and sensitivity to frequency offset. Both analysis and simulation results show that various parameter adaptations can be made with respect to the channel state information to improve the system performance.QC 20110914</p
Multi-bandwidth analog filter design for SDR
No full textSoftware Defined Radio (SDR) becomes more and more popular due to the requirement of multi-standard communication. In the front end, the increasing demand for multi-mode wireless communication necessitates low cost, highly integrated and multi-bandwidth analog circuits to be implemented. This paper presents an overview on the consideration of Intermediate Frequency (IF) filter design for five communication standards: GSM, WCDMA, 802.11b, 802.11g and WiMAX. A transistor level multi-bandwidth IF Gyrator-C filter is designed. Through the frequency response we can analyze the filter channel selection for different standards.</p
A Matlab/Octave Simulation Workbench for Multi-Antenna Software Defined Radio
No full textThe current paper describes a generic workbench for multiple antennas Software Defined Radio (SDR) system in Matlab or Octave. The workbench is functionally modularized and make use of parameter lists for reconfiguration. Currently, it supports both narrow band MIMO systems and OFDM-based wideband systems with single or multiple antennas. It could also be easily extended to accommodate other wireless or wireline standards, such as GSM, WCDMA, xDSL, DVB-x, Wimax, Bluetooth, etc.</p
Pulse Shape Adaptivity in OFDM/OQAM Systems
No full textAdaptation is crucial to realise high data rate transmission in multicarrier communication systems over dispersive channels. Apart from rate/power adaptation enabled by orthogonal frequency division multiplexing (OFDM), OFDM/offset QAM (OFDM/OQAM) systems provide possibility to adjust pulse shapes depending on the channel characteristics. In this paper we discuss and evaluate pulse shape adaptivity in OFDM/OQAM systems with focus on the extended Gaussian functions (EGF) which have been shown to be good candidates for pulse shape adaptation. By investigating the time frequency dispersion robustness and carrier frequency offset sensitivity, both analysis and simulation results show that pulse shape adaptation with respect to the channel state information can improve the system performance.QC 20111108</p
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