Study of Electronic Control and Real Behavior in Variable Filtering and Oscillating Applications of Modern Active Elements

Práce pojednává o elektronicky nastavitelných a konfigurovatelných aplikacích moderních aktivních prvků. Velmi často jsou prezentovány rozmanité aktivní prvky v aplikacích filtrů a oscilátorů, které víceméně vychází ze základních a vesměs podobných principů syntézy a návrhu, avšak není provedena detailní studie reálného chování a možností elektronického řízení parametrů. Při precizním návrhu aplikace je však důležité identifikovat problémové vlastnosti a stanovit, jak moc ovlivní funkci zařízení. Je zde srovnáváno několik filtračních struktur založených na běžných i modifikovaných principech integrátorové syntézy z pohledu konfigurovatelnosti, variabilnosti a druhu použitého elektronického řízení. K řízení jsou využívány standardní metody, jako je změna transkonduktance, změna vstupního (intrinzického) odporu proudových svorek a již méně typická možnost řízení pomocí proměnného proudového zesílení. Ta poslední metoda řízení umožnila objevit zcela unikátní filtr s elektronickou změnou přenosu z PZ na FČ, který jednoduchostí překonává běžnější integrátorové struktury, kde je zapotřebí fyzické přepojení v obvodu. Větší část práce je věnována elektronicky řiditelným oscilátorům, a to hlavně kvadraturním. Je prezentováno několik velice jednoduchých typů, které vyžadují nejmenší množství aktivních i pasivních prvků, i složitějších koncepcí, které již vyžadují více aktivních prvků, ale odstraňují některé nevýhody jednoduchých variant. Především je i zde kladen důraz na studium reálného chování, které objasňuje různé problémy se vzájemnou závislostí oscilační podmínky a oscilačního kmitočtu, závislostí amplitudy kvadraturních oscilátorů na ladícím parametru, vlivu změny ladícího parametru na plnění oscilačních podmínek, atd. V rámci této části byl definován nový typ či modifikace aktivního prvku tzv. current-gain-controlled current conveyor transconductance amplifier (CGCCCTA). Požadavek na nové aplikace zejména v oblastí oscilátorů pro Ústavem telekomunikací nově vyvíjený proudový zesilovač a digitálně řízený proudový zesilovač nechal vzniknout několika kapitolám práce, kde může být tento prvek výhodně použit. Podstatný přínos, který je důležitý především pro praxi, spočívá v testování většiny navržených obvodů experimentálně a stanovení přesných návrhových vztahů, které zohledňují reálné chování obvodu a potvrzují experimenty získané výsledky.The thesis deals with electronically adjustable and configurable applications of the modern active elements. In the field there were presented various active elements in applications of the analog filters and oscillators which stem from basic and more or less similar principles of circuit synthesis and design. However, there is not provided study of real behavior in detail and in most cases electronic control of the various parameters in application is not verified. In the precise design of application is very important to identify problematic features and determine how much it influences functionality of the device. In this work several filtering structures based on common and modified synthesis principles (integrator loops) are compared in the view of multifunctionality, configurability, variability, kind of used electronic control and impact of influences of real elements on behavior. There are used standard methods like adjusting of variable transconductance, intrinsic value of current input resistance and not so common method based on variable current gain in design of modified and improved multifunctional filtering circuits. The last method of mentioned control enabled to find quite unique filter which allows continuous electronic change of transfer from band-reject to all-pass filter of the 2nd order without reconnection. It is much simpler than previous and more common integrator loops. Larger part of this work is focused on electronically controllable oscillators mainly on quadrature types. There is presented several very simply and elementary realizations which require minimal number of active and passive elements. There are also slightly or more complicated solutions which remove some drawbacks of mentioned simpler variants. First of all there is given attention on study of real behavior which make obvious different problems with mutual dependence of oscillation condition and oscillation frequency, dependence of produced amplitudes (quadrature types) on parameter which is controlling oscillation frequency, influence of this parameter on oscillation condition, etc. In the framework of this part of the thesis there was introduced a novel modification of current conveyor transconductance amplifier (CCTA) so called current-gain-controlled current conveyor transconductance amplifier (CGCCCTA). Requirements for novel applications in the field of oscillators for newly developed controllable current amplifier and digitally controllable current amplifier (DACA) at the Department of Telecommunication FEEC BUT lead to creation of several chapters of this work where mentioned active elements can be used. The important contribution of this work (for practical approach) is also experimental testing of most of designed circuits and determination of exact design equations and rules which take into account real behavior of circuits and confirm results obtained from experiments.

Multifunctional tuned active filter

Diplomová práce se zabývá návrhem ARC multifunkčních filtrů používajících moderní funkční bloky. Tyto bloky jsou například rychlé napěťové operační zesilovače (OZ), transadmitanční zesilovače (OTA), proudové konvejory (CCII) nebo proudové analogové násobičky, transimpedanční zesilovače (CFA), integrované obvody se stavebními bloky na principu spínaných kapacitorů a digitální potenciometry. Zapojení filtrů jsou studována s ideálními obvodovými modely aktivních bloků a s modely 3. úrovně založenými na napětím řízených zdrojích napětí, napětím řízených zdrojích proudů atd. Používané profesionální makromodely jsou například LT 1364 (Linear Technology), EL 2045 (Intersil), LT 1228 (Linear Technology), LM 13700 (National Semiconductor), EL 2082 (Intersil), AD 844 (Analog Devices) a další. Zapojení navržených filtrů jsou podrobena simulacím v PSpice, kde jsou studovány parazitní vlastnosti a vliv reálných funkčních bloků. Simulacemi jsou zkoumány a ověřovány možnosti elektronického ladění a řízení parametrů těchto filtrů. Vlastnosti některých simulovaných obvodů jsou srovnány s experimentálními výsledky. Na závěr jsou vlastnosti uvedených filtrů porovnány. Konstrukční (výrobní) náležitosti některých filtrů jsou uvedeny na konci práce.The diploma thesis deals about design of the ARC multifunctional filters using modern functional blocks. These active blocks are for example voltage feedback operational amplifiers (OAs), operational transconductance amplifiers (OTAs), current conveyors (CCIIs) or current mode analog multipliers, current feedback amplifiers (CFAs), integrated circuits with switched capacitors building blocks (SCs) and digital potentiometers. The filters are studied with ideal circuit models and models of third level (3) based on voltage controlled voltage sources, voltage controlled current sources etc. (analog behavioral modelling). The professional macromodels are used for example LT 1364 (Linear Technology), EL 2045 (Intersil), LT 1228 (Linear Technology), LM 13700 (National Semiconductor), EL 2082 (Intersil), AD 844 (Analog Devices) and others. The circuits of the designed filters are simulated in PSpice (OrCAD), parasite effects and effects of the real parts are studied. Tuning and electronic adjusting parameters these filters are discussed and controlled by simulation in PSpice. Properties some simulated circuits are compare with experimental results. In conclusion individual filters are discussed and compared their properties. The constructional details of the some filters are presented at the end of this work.

Tunable Fractional-Order Capacitance Multiplier Using Current Gain Adjustment

This paper brings new solution of linearly adjustable fractional-order capacitance multiplier. The adjustable current gain, linear in wide range of input current and with linear dependence on driving voltage, serves for these purposes and offers one-decade variation of equivalent capacity (pseudo-capacitance) between 24 and 429 F/sec^0.75 . The operational range was tested by PSpice simulations and by measurement using RC approximant of constant phase element of the order 0.25 in bandwidth from 20 Hz up to 1 MHz

CMOS Current Feedback Operational Amplifier-Based Relaxation Generator for Capacity to Voltage Sensor Interface

This paper presents a simple relaxation generator, suitable for a sensor interface, operating as a transducer of capacitance to frequency/period. The proposed circuit employs a current feedback operational amplifier, fabricated in I3T25 0.35 m ON Semiconductor CMOS process, and four passive elements including a grounded capacitor (the sensed parameter). It offers a low-impedance voltage output of the generated square wave. Additional frequency to DC voltage converter offers output information in the form of voltage. The experimental capacitance variation from 6.8 nF to 100 nF yields voltage change in the range from 21 mV to 106 mV with error below 5% and sensitivity 0.912 mV/nF evaluated over the full range of change. These values are in good agreement with simulation results obtained from the Mathcad model of frequency to DC voltage transducer passive circuit

Design of Signal Generators Using Active Elements Developed in I3T25 CMOS Technology Single IC Package for Illuminance to Frequency Conversion

This paper presents a compact and simple design of adjustable triangular and square wave functional generators employing fundamental cells fabricated on a single integrated circuit (IC) package. Two solutions have electronically tunable repeating frequency. The linear adjustability of repeating frequency was verified in the range between 17 and 264 kHz. The main benefits of the proposed generator are the follows: A simple adjustment of the repeating frequency by DC bias current, Schmitt trigger (threshold voltages) setting by DC driving voltage, and output levels in hundreds of mV when the complementary metal-oxide semiconductor (CMOS) process with limited supply voltage levels is used. These generators are suitable to provide a simple conversion of illuminance to frequency of oscillation that can be employed for illuminance measurement and sensing in the agriculture applications. Experimental measurements proved that the proposed concept is usable for sensing of illuminance in the range from 1 up to 500 lx. The change of illuminance within this range causes driving of bias current between 21 and 52 mu A that adjusts repeating frequency between 70 and 154 kHz with an error up to 10% between the expected and real cases

Electronically Tunable Oscillator Utilizing Reinforced Controllable Parameters

This paper presents a novel solution of an oscillator with electronically adjustable oscillation condition (CO) and frequency of oscillations (FO). Oscillation condition is controlled by current gain and frequency of oscillations is adjustable by transconductance and intrinsic resistance of used active elements. Both CO and FO are mutually independent. Moreover, special feature of CO allows boosting parameter driving FO (transconductance) and then shifting the whole FO range to higher bands. It allows to keep values of passive elements (capacitors especially) in satisfactory range even for higher value of FO. Simulations in PSpice confirms this hypothesis

Various Order Low–Pass Filter with the Electronic Change of Its Approximation

A design of a low pass frequency filter with the electronic change of the approximation characteristics of resulting responses is presented. The filter also offers the reconnection–less reconfiguration of the order (1st, 2nd, 3rd and 4th order functions are available). Furthermore, the filter offers the electronic control of the cut–off frequency of the output response. The feature of the electronic change of the approximation characteristics has been investigated for Butterworth, Bessel, Cauer, Chebyshev and Inverse Chebyshev approximations. The design is verified by PSpice simulations and experimental measurements. The results are also supported by the transient domain response (response to the square waveform), comparison of group delay, sensitivity analysis and implementation feasibility based on given approximation. The benefit of the proposed electronic change of the approximation characteristics feature (in general signal processing or for sensors in particular) has been presented and discussed for an exemplary scenario

Electronically Reconfigurable and Tunable Fractional-Order Filter Using Resonator Concept and Feedforward Path for Low-Frequency Tone Signalization

A novel electronically reconfigurable fractional-order filter allowing independent electronic frequency tuning and switchless change of the transfer response by a single parameter between standard band-pass, inverting all-pass response and special type band-reject response is presented in this work. The differences between these special transfer characteristics and standard features consist in magnitude and phase response behavior. Inverting amplification or attenuation is also available. The filter has tested frequency range between 1 Hz and 100 kHz. The proposed fractional-order filter (using two fractional-order element having equivalent capacity 8.7 uF/sec^1/4, =3 /4) tunability yields one-decade range approximately between 10 Hz and 100 Hz by transconductance between 0.19 and 1.1 mS (fractional-order design helps with reduction of driving force less than one decade). The application example in frequency/phase detector (operationability around center frequency 100 Hz - between 50 and 180 Hz) and further signaling frequency detecting system for frequency shift keying demodulator offers maximal detectable voltage (about 300 mV) for alignment (zero phase shift) of the signals of the same frequency (center frequency of the proposed filter in inverting all-pass mode). It also offers an interesting application in frequency shift keying demodulation process (or for identification/signalization purposes of certain frequencies) by usage of a simple additional comparator generating clear output state. Cadence simulations as well as experimental tests using integrated cells of special multipliers fabricated in ON Semiconductor 0.35 m I3T25 CMOS process confirm operationability of the proposed concept as well as simple application of special response of the filter for phase/frequency detection and demodulation purposes