Fully-Differential Frequency Filters with Modern Active Elements

Tato disertační práce se zaměřuje na výzkum v oblasti frekvenčních filtrů. Hlavním cílem je navrhnout a analyzovat plně diferenční kmitočtové filtry pracující v proudovém módu a využívající moderní aktivní prvky. Prezentované filtry jsou navrženy za použití proudových sledovačů, operačních transkonduktančních zesilovačů, plně diferenčních proudových zesilovačů a transrezistančních zesilovačů. Návrh se zaměřuje na možnost řídit některý z typických parametrů filtru pomocí řiditelných aktivních prvků, které jsou vhodně umístněny do obvodové struktury. Jednotlivé prezentované filtry jsou navrženy v nediferenční a diferenční verzi. Velký důraz je věnován srovnání plně diferenčních struktur s jejich odpovídajícími nediferenčními formami. Funkčnost jednotlivých návrhů je ověřena simulacemi a v některých případech i experimentálním měřením.This doctoral thesis focuses on research in the field of frequency filters. The main goal is to propose and analyze fully-differential current-mode frequency filters employing modern active elements. Presented filters are proposed using current followers, operational transconductance amplifiers, digitally adjustable current amplifiers and transresistance amplifiers. The proposal is focusing on ability to control some of the typical filter parameter or parameters using controllable active elements suitably placed in the circuit structure. Individual presented filters are proposed in their single-ended and fully-differential forms. Great emphasis is paid to a comparison of the fully-differential structures and their corresponding single-ended forms. The functionality of each proposal is verified by simulations and in some cases also by experimental measurements.

Non-linear circuit structures with active current elements

Tento projekt se zabývá nelineárními obvodovými strukturami s proudovými aktivními prvky. Úvod práce se zabývá popisem proudového konvejeru. Dále se text věnuje problematice obvodů pro zpracování signálů v analogové technice. Nejdříve jsou popsány obvody diodových omezovačů a měničů. Velký důraz je kladen na usměrňovače s proudovými aktivními prvky. V závěru práce jsou realizovány obvody univerzálního přesného dvoucestného usměrňovače s použitím operačního zesilovače a proudového konvejeru a provedeno jejich srovnání.This thesis deals with non-linear curcuit structures with current active elements. In its introduction this work deals with a description of the current conveyor. Further the text pays attention to the possiblities of the circuits for modification signals in analogue technology. First are described circuits of diode limiters and transducer. Great attention is paid to the amplifiers with current active parts. In conclusion are realized circuits of universal precise full-wave rectifiers using operational amplifier and current conveyor and made comparisons.

Nonlinear circuits using current active elements

Tato práce se zabývá nelineárními obvodovými strukturami s proudovými aktivními prvky. Úvod práce se zabývá popisem proudového aktivních prvků, jako jsou proudový konvejor, transkonduktanční operační zesilovač a proudový sledovač. Dále se text věnuje problematice obvodů pro zpracování signálů v analogové technice. Na začátku jsou popsány obvody diodových omezovačů a měničů. Velký důraz je kladen na usměrňovače s proudovými aktivními prvky. Jsou navrženy odsimulovány a zrealizovány obvody univerzálního přesného dvoucestného usměrňovače s použitím operačního zesilovače a proudového konvejoru a provedeno srovnání známých a navržených obvodových řešení. V práci jsou také zmíněny další obvodové struktury s použitím proudových aktivních prvků, jako násobič, dělič, generátor trojúhelníkového signálu a oscilátory.This thesis deals with non-linear curcuit structures with current active elements. In its introduction this work deals with a description of the current active elements, such as current conveyor, transconductance operational amplifier and current follower. Further the text pays attention to the possiblities of the circuits for modification signals in analogue technology. First are described circuits of diode limiters and transducer. Great attention is paid to the amplifiers with current active elements. Are propřed simulated and practically realized circuits of universal precise full-wave rectifiers using operational amplifier and current conveyor and made comparisons of known and proposed circuits. The paper also discussed other circuit structures using of current active elements, such as multiplier, divider, a triangular signal generator and oscillators.

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

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 Tunable Fully-Differential Fractional-Order Low-Pass Filter

The paper presents proposal of a fully- differential (1 + )-order low-pass filter. The order of the filter and its cut-off frequency can be controlled electronically. The filter is proposed using operational transconductance amplifiers (OTAs), adjustable current amplifiers (ACAs) and fully-differential current follower (FD-CF). The circuit structure is based on well-known Inverse Follow-the-Leader Feedback (IFLF) topology. Design correctness of the proposed filter is supported by PSpice simulations with transistor-level simulation models. The ability of the electronic control of the order has been tested for five individual values of parameter . Furthermore, the ability of the electronic control of the cut-off frequency of the filter has been also tested for five different values. Additionally, the simulation results of the proposed fully-differential (F-D) filter are compared with the results of the single-ended (S-E) equivalent of the presented filter

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