Inverse-follow-the-leader-feedback Research Articles

Electronically Tunable Fully-Differential Fractional-Order Low-Pass Filter

The paper presents proposal of a fully-differential (1 + α)-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 α. 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.DOI: http://dx.doi.org/10.5755/j01.eie.23.3.18332

Design for testability of high‐order OTA‐C filters

SummaryA study of oscillation‐based test for high‐order Operational Transconductance Amplifier‐C (OTA‐C) filters is presented. The method is based on partition of a high‐order filter into second‐order filter functions. The opening Q‐loop and adding positive feedback techniques are developed to convert the second‐order filter section into a quadrature oscillator. These techniques are based on an open‐loop configuration and an additional positive feedback configuration. Implementation of the two testability design methods for nth‐order cascade, IFLF and leapfrog (LF) filters is presented, and the area overhead of the modified circuits is also discussed. The performances of the presented techniques are investigated. Fourth‐order cascade, inverse follow‐the‐leader feedback (IFLF) and LF OTA‐C filters were designed and simulated for analysis of fault coverage using the adding positive feedback method based on an analogue multiplexer. Simulation results show that the oscillation‐based test method using positive feedback provides high fault coverage of around 97%, 96% and 95% for the cascade, IFLF and LF OTA‐C filters, respectively. Copyright © 2016 John Wiley & Sons, Ltd.

Performance comparison of high-order IFLF and LF linear phase lowpass OTA-C filters with and without gain boost

Design and performance comparison of high-order operational transconductance amplifier and capacitor (OTA-C) filters using leapfrog (LF) and inverse-follow-the-leader-feedback (IFLF) structures are investigated. The filters are designed for a 125 MHz seventh-order equiripple group delay lowpass characteristic with and without gain boost and simulated in 0.25 μm 2-V CMOS. A fully differential highly linear OTA with cross-coupled input pairs and regulated cascode output is used for the simulation. Simulated results show that while the IFLF OTA-C filter can achieve a higher gain boost, the LF OTA-C filter has better other performances.

PERFORMANCE ANALYSIS AND COMPARISON OF MULTIPLE LOOP FEEDBACK OTA-C FILTERS

This paper is concerned with performance analysis and comparison of multiple loop feedback (MLF) operational transconductance amplifier and capacitor (OTA-C) filters. General formulas for analysis of sensitivity, maximum input signal and noise based on the matrix method of MLF OTA-C filters are derived for canonical and noncanonical all-pole and finite transmission zero architectures. These formulas can be readily used for performance evaluation of any MLF filters. For illustrating the use of the formulas and comparison of different structures, the performances of inverse-follow-the-leader-feedback (IFLF), leapfrog (LF), and cascade MLF OTA-C filters are simulated ideally and at CMOS transistor level, realizing the same lowpass Butterworth characteristic and using the same OTA. Results show that the LF filter has the lowest passband magnitude sensitivity, highest maximum input signal, and best magnitude response, whilst the cascade filter has the lowest group delay sensitivity, best noise performance and best group delay response. Results also reveal that the IFLF filter has better passband magnitude sensitivity than the cascade filter and better passband group delay sensitivity than the LF filter, but it is the worst in other performances.

Structure generation and performance comparison of elliptic Gm‐C filters

AbstractStarting from a set of matrices describing a general Gm‐C filter topology, a procedure is developed for generating structures of lowpass filters. As the matrices and the filter topologies have a one‐to‐one correspondence, an algebraic method is used to identify filter topologies with desired properties, here, transfer functions with finite jω‐axis transmission zeros, specifically elliptic filters. Sensitivity expressions for these structures are derived and a performance comparison based on a set of chosen criteria is made. For a specified elliptic transfer function, filters with only grounded capacitors and those containing also floating capacitors emerge as alternative realizations, as are filters with a single input and those with distributed inputs. For third‐order functions, a detailed comparison is performed of leapfrog (LF) and inverse follow‐the‐leader‐feedback (IFLF), the most popular special cases, and of topologies that have also floating capacitors (LFf, IFLFf), as well as of a novel configuration that uses also distributed inputs (DIf) and leads to a reduced element count. Design guidelines and restrictions are given, which follow from the derived results with focus on the circuits' sensitivity performance and other properties important for IC implementation. Copyright © 2004 John Wiley & Sons, Ltd.

Performance comparison of high-order IFLF and cascade analogue integrated lowpass filters

The magnitude and delay performance of integrated continuous-time gm–C lowpass filters is discussed. The analysis is based on tenth-order filters with equiripple group delay, implemented in CMOS fully differential form as inverse-follow-the-leader feedback (IFLF) and cascade topologies. A very-high-frequency operational transconductance amplifier (OTA) is used as the basic building block. The sensitivity performance is assessed by simulating IFLF and cascade filters with 27 real CMOS models released from MOSIS. Experimental and simulation results show that the passband magnitude sensitivity of the cascade filter is larger than that of the IFLF filter. In the stopband, the opposite is true. The results demonstrate that the group delay performance, on the other hand, is worse in the IFLF filter than in the cascade filter.

Switched-capacitor filter design using the composite discrete integrator

This paper describes the design of switched-capacitor (SC) filters by the use of a discrete integrator called the composite discrete integrator (CDI). Despite the fact that the CDI is more complicated than well-known integrators such as the bilinear discrete integrator (BDI) and the lossless discrete integrator (LDI), it offers high frequency advantages by minimizing discrete integrator errors. Cascade, inverse-follow-the-leader-feedback (IFLF), and ladder filter design techniques are presented. Simulation results of the filter examples are also given.

Low-sensitivity realization of switched-capacitor filters

Two low-sensitivity switched-capacitor filter structures implementing the strays-insensitive switched-capacitor biquads are presented. They are based on a generalized multiple-loop-feedback (GMF) topology, which is formed by the combination of the follow-the-leader-feedback (FLF) and inverse follow-the-leader-feedback (IFLF) topologies. Design equations that relate the feedback and feedforward parameters to the discrete-time transfer function are derived for both structures. Sensitivity analyses of the proposed structures as well as of the previously published ones are carried out using Monte Carlo simulations. It was found that the modified GMF structure possesses a lower sensitivity with respect to capacitance ratios.