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.

Frequency Filters with Current Active Elements

Disertační práce se orientuje především na výzkum nových proudových aktivních prvků a jejich aplikace v kmitočtových filtrech, vhodných pro proudový mód. Práce je zaměřena na návrh nových zapojení filtrů vhodných nejen pro tradiční nediferenční režim zpracování signálů, ale i struktur pro plně diferenční zpracování. V práci jsou navrženy tři obecné koncepce typu KHN filtrů druhého řádu, v nichž je řiditelnost činitele jakosti a kmitočtu komplexně sdružených pólů zajištěna pomoci několika vhodně zařazených řiditelných proudových zesilovačů. Dalšími použitými aktivními prvky jsou proudový konvejor druhé generace, vícevýstupový proudový sledovač, transkonduktanční zesilovač a jejich diferenční obdoby. Z obecných struktur je možné odvodit velké množství řešení a některá z nich jsou prezentována i v této práci. V práci je dále prezentováno několik multifunkčních a také jednoúčelových filtračních struktur druhého řádu a dvě varianty syntetických prvků n-tého řádů, se kterými je možné navrhnout filtry vyšších řádů, jak v nediferenční, tak i diferenční podobě.This doctoral thesis is focused mainly on research of new current active elements and their applications in frequency filters suitable for current-mode. Work is focused on design of new filtering structures suitable for traditional single-ended signal processing and also on structures suitable for fully-differential applications. The thesis contains three designed general conceptions of KHN-type second-order filters. Adjustability of quality factor and pole frequency is provided by controllable current amplifiers that are placed properly in designed structures. Structures also contain second-generation current conveyors, multiple-output current followers, transconductance amplifiers and their fully-differential equivalents. There are lot of possible solutions that could be obtained from general structures, some of them are presented in the work. The thesis also presents several multifunctional and also single-purpose filtering structures of second-order and two variants of n-th order synthetic elements which are suitable to realize higher order filters both in single ended and fully differential type. In each case, functionality of new solutions is verified by simulations and in several cases also by real measurement.

Reconfigurable Receiver Front-Ends for Advanced Telecommunication Technologies

The exponential growth of converging technologies, including augmented reality, autonomous vehicles, machine-to-machine and machine-to-human interactions, biomedical and environmental sensory systems, and artificial intelligence, is driving the need for robust infrastructural systems capable of handling vast data volumes between end users and service providers. This demand has prompted a significant evolution in wireless communication, with 5G and subsequent generations requiring exponentially improved spectral and energy efficiency compared to their predecessors. Achieving this entails intricate strategies such as advanced digital modulations, broader channel bandwidths, complex spectrum sharing, and carrier aggregation scenarios. A particularly challenging aspect arises in the form of non-contiguous aggregation of up to six carrier components across the frequency range 1 (FR1). This necessitates receiver front-ends to effectively reject out-of-band (OOB) interferences while maintaining high-performance in-band (IB) operation. Reconfigurability becomes pivotal in such dynamic environments, where frequency resource allocation, signal strength, and interference levels continuously change. Software-defined radios (SDRs) and cognitive radios (CRs) emerge as solutions, with direct RF-sampling receivers offering a suitable architecture in which the frequency translation is entirely performed in digital domain to avoid analog mixing issues. Moreover, direct RF- sampling receivers facilitate spectrum observation, which is crucial to identify free zones, and detect interferences. Acoustic and distributed filters offer impressive dynamic range and sharp roll off characteristics, but their bulkiness and lack of electronic adjustment capabilities limit their practicality. Active filters, on the other hand, present opportunities for integration in advanced CMOS technology, addressing size constraints and providing versatile programmability. However, concerns about power consumption, noise generation, and linearity in active filters require careful consideration.This thesis primarily focuses on the design and implementation of a low-voltage, low-power RFFE tailored for direct sampling receivers in 5G FR1 applications. The RFFE consists of a balun low-noise amplifier (LNA), a Q-enhanced filter, and a programmable gain amplifier (PGA). The balun-LNA employs noise cancellation, current reuse, and gm boosting for wideband gain and input impedance matching. Leveraging FD-SOI technology allows for programmable gain and linearity via body biasing. The LNA's operational state ranges between high-performance and high-tolerance modes, which are apt for sensitivityand blocking tests, respectively. The Q-enhanced filter adopts noise-cancelling, current-reuse, and programmable Gm-cells to realize a fourth-order response using two resonators. The fourth-order filter response is achieved by subtracting the individual response of these resonators. Compared to cascaded and magnetically coupled fourth-order filters, this technique maintains the large dynamic range of second-order resonators. Fabricated in 22-nm FD-SOI technology, the RFFE achieves 1%-40% fractional bandwidth (FBW) adjustability from 1.7 GHz to 6.4 GHz, 4.6 dB noise figure (NF) and an OOB third-order intermodulation intercept point (IIP3) of 22 dBm. Furthermore, concerning the implementation uncertainties and potential variations of temperature and supply voltage, design margins have been considered and a hybrid calibration scheme is introduced. A combination of on-chip and off-chip calibration based on noise response is employed to effectively adjust the quality factors, Gm-cells, and resonance frequencies, ensuring desired bandpass response. To optimize and accelerate the calibration process, a reinforcement learning (RL) agent is used.Anticipating future trends, the concept of the Q-enhanced filter extends to a multiple-mode filter for 6G upper mid-band applications. Covering the frequency range from 8 to 20 GHz, this RFFE can be configured as a fourth-order dual-band filter, two bandpass filters (BPFs) with an OOB notch, or a BPF with an IB notch. In cognitive radios, the filter’s transmission zeros can be positioned with respect to the carrier frequencies of interfering signals to yield over 50 dB blocker rejection