Current Follower Research Articles

A Floating Decremental/ Incremental Meminductor Emulator Using Voltage Differencing Inverted Buffered Amplifier and Current Follower

This paper presents a floating meminductor emulator circuit using a voltage differencing inverted buffered amplifier (VDIBA), current follower (CF), and two grounded capacitors. The parasitic resistance at the input terminal of the current follower has been utilized. The idea of implementing a meminductor emulator is simple and works on the principle of putting memory inside the active inductor circuit. A capacitor (memory element) has been charged by the current flowing through the active inductor circuit. Therefore, the proposed meminductor emulator can be viewed as an active inductor circuit having memory inside it. The proposed floating meminductor emulator works over a significant range of frequencies and satisfies all the characteristics of a meminductor. The meminductor emulator has been realized and simulated in the LTspice simulation tool using TSMC’s 180-nm CMOS technology parameters. A chaotic oscillator circuit has been realized using the proposed meminductor emulator to verify its performance. The results obtained for the chaotic oscillators are found to be satisfactory and thus verify the performance of the proposed meminductor emulator.

Novelty Search for the Synthesis of Current Followers

A topology synthesis method is introduced using genetic algorithms (GA) based on novelty search (NS). NS is an emerging meta-heuristic, that guides the search based on the novelty of each solution instead of the objective function. The synthesized topologies are current follower (CF) circuits; these topologies are new and designed using integrated circuit CMOS technology of 0.35m. Topologies are coded using a chromosome divided into four genes: small signal gene (SS), MOSFET synthesis gene (SMos), polarization gene (Bias) and current source synthesis gene (CM). The proposed synthesis method is coded in MatLab and uses SPICE to evaluate the CFs fitness. The GA based on NS (GA-NS) is compared with a standard objective-based GA, showing unique search dynamics and improved performance. Experimental results show twelve CFs synthesized by the GA-NS algorithm, and their main attributes are summarized and discussed. This work is the first to show that NS can be used asa promising alternative in the field of automatic circuit synthesis.

Binary Genetic Encoding for the Synthesis of Mixed-Mode Circuit Topologies

A binary genetic encoding (BGE) representation for the automatic synthesis of mixed-mode circuit topologies, is introduced. First, the genetic encoding of unity-gain cells (UGCs), such as voltage (VF) and current followers (CF), and voltage (VM) and current mirrors (CM), is presented. New BGEs for the VM and CM are introduced. Second, the UGC’s chromosomes are combined to synthesize mixed-mode circuit-topologies, namely current conveyors and current-feedback operational amplifiers (CFOA). Five strategies for the combination or superimposing of UGCs are introduced. The proposed BGE has been implemented in MATLABTM, and links SPICE to evaluate the populations with different integrated circuit technologies. Some new synthesized circuit topologies are shown along with their chromosome description.

Pathological realizations of the DCVC (CDBA) and applications to oscillators and filters

The historical origin of the introduction of the differential current voltage conveyor (DCVC) also known as the current differencing buffered amplifier (CDBA) is reviewed. Pathological realizations of the modified differential current conveyor (MDCC) and of the DCVC are given. Generation of alternative equivalent oscillator and filter circuits using voltage followers (VF), current followers (CF), voltage inverters (VI) and current inverters (CI) from known CDBA oscillators and filters is demonstrated by several examples. It is found that there is duplication in some of the recently published circuits and new simplified oscillator and filter circuits are reported.

Realization of Current-Mode KHN-Equivalent Biquad Using Current Follower Transconductance Amplifiers (CFTAs)

In this letter a new active element the Current Follower Transconductance Amplifier (CFTA) for the realization of the current-mode analog blocks is presented. The element is a combination of the Current Follower (CF) and the Balanced Output Transconductance Amplifier (BOTA). Possible internal structure of the CFTA is presented. The usage of the new active element is shown on the design of the Kerwin-Huelsman-Newcomb (KHN) structure working in the current mode. The frequency filter using the CFTA elements has been designed using the signal-flow graphs. The circuit structure employs three CFTA elements and two grounded passive elements. The filter enables realizing not only the basic functions as the low- (LP), band- (BP) and high-pass (HP) but also the notch and all-pass (AP) filter. The advantage of the structure presented is that the outputs of the filter are at high impedance and hence it is not necessary to use other auxiliary active elements. The properties of the filter proposed were verified by sensitivity and AC analyses in the PSPICE program.

On the Realization of Simulated Inductors with Reduced Parasitic Impedance Effects

In this paper, a method for reducing the parasitic impedance effects of the current feedback operational amplifiers (CFOAs) in an inductor simulator at low frequencies is proposed. Also, two novel grounded inductors employing a current follower (CF) and a second generation current conveyor (CCII) are given to illustrate the parasitic reduction technique clearly. The low frequency restrictions of the proposed inductors due to terminal parasitic resistances can be improved by using the presented parasitic impedance reduction technique. SPICE simulations show that the presented inductor employing CFOAs in a voltage-mode (VM) band-pass and high-pass filter application has lower parasitic effects at low frequencies. In addition to simulation results, experimental test results are given to verify the theory.

Synthesis of CCII-s by superimposing VFs and CFs through genetic operations

It is introduced a new genetic algorithm to synthesize the negative-type second generation current conveyor (CCII-) by superimposing a voltage follower (VF) with a current follower (CF). First, the VF and CF are described by binary genes. Second, the gene CF is inverted, rigth-shifted and multiplied (AND operation) with the gene VF to verify that both genes can be superimposed to synthesize the CCII-. Finally, some synthesized CCII-s are presented which electrical characteristics are measured using HSPICE and standard CMOS technology of 0.35µm.

Designing SRCOs by combining SPICE and Verilog-A

The design of single-resistance-controlled oscillators (SRCOs) is presented by using current followers (CF) and voltage followers (VF). First, the design of the followers is described by using SPICE and standard CMOS technology of 0.35 µm. Second, a SRCO is simulated in SPICE by using the designed CF and VF. Third, the SRCO is simulated in Verilog-A by using ideal and real behavioural models for the followers. Finally, the good agreement on the simulation results leads us to conclude on the usefulness to combine SPICE and Verilog-A to enhance analogue integrated circuit design.

SITO electronically tunable high output impedance current-mode universal filter

A novel current-mode (CM) single-input and three-output (SITO) universal filter using two second generation current controlled conveyors (CCCIIs), one current follower (CF) and two capacitors is presented. The circuit is fully programmable and implements all the five generic filtering functions. The lowpass (LP), bandpass (BP), and highpass (HP) functions can be realized simultaneously while Notch (BS) and allpass (AP) responses can be implemented simply by connecting the appropriate node currents without requiring additional elements. The availability of currents at high impedances, facilitate cascadibility feature. The filter performance factors ?0 and ?0/Q are electronically tunable through separate bias currents of the CCCIIs. SPICE simulation results are included to confirm the workability of the proposed circuit.

Synthesis of VFs and CFs by Manipulation of Generic Cells

A synthesis methodology to search on all realisations of CMOS voltage followers (VFs) and current followers (CFs), is introduced by manipulation of generic cells. Nullators are used to model the ideal behaviour of generic VFs, and norators for generic CFs. Norators and nullators are added until to form joined nullator-norator pairs, which are further biased and synthesized by transistors. Finally, two generated topologies performing good follower behaviour are selected to synthesize the CCII- and an oscillator, for which SPICE simulation results are given.

New universal filter using only current followers as active elements

A new universal current-mode (CM) biquad filter is presented which can realise all the five standard filter functions namely lowpass, bandpass, highpass, notch and allpass employing only unity-gain current followers (CF) as active elements. The workability of the proposed universal biquad, realised with CMOS unity-gain current followers, is established by SPICE simulations. The new circuit provides explicit CM outputs from high output impedance terminals and possesses a number of advantageous features all of which are not available simultaneously in any of the previously reported CF-based universal biquad filters.

Current-mode biquad using OTAs and CF

A novel current-mode biquad using operational transconductance amplifiers (OTAs) and current follower (CF) is presented. The circuit can realise lowpass, bandpass, highpass, band-stop and all-pass transfer functions without any circuit matching conditions. The circuit parameters can also be tuned independently by the transconductance gains of the OTAs. The proposed biquad enjoys very low sensitivities with respect to the circuit elements.

Novel universal current-mode filters using unity-gain cells

Two novel universal current-mode filters using unity-gain current followers (CFs) and voltage followers (VFs) are presented. The first one, employing three CFs, one VF, two grounded capacitors and two resistors, has two inputs and three outputs. The second one, employing only two CFs, one VF, two grounded capacitors and two resistors, has four inputs and a single output. Both proposed circuits oOEer the following advantageous features: universal current-mode filter realization from the same configuration, no requirements of component matching conditions, employment of two grounded capacitors ideal for integration, employment of two virtually grounded resistors good for voltage control, easy adjustment of ω0/Q and ω0 through separate virtually grounded resistors and low active and passive sensitivity performance.

A multiple output active filter based on current followers

In this paper a multiple output current follower (CF)-based active filter (MOCFF) is presented. The construction of basic filtering oriented biquadratic transfer functions (low-pass, high-pass, band-pass, band-notch and all-pass) is realized by means of two independent stages of identical topology. Each of them incorporates three CFs appropriately interconnected with R,C branches; a CF-based adder (CFA) in conjunction with a versatile CF-incorporating mutual feedback symmetric circuit (MFSC) implement three different frequency responses. The pair of CFs composing the MFSC should be visualized as a voltage transfer function generator. The MOCFFs salient feature is the current-based signal processing while voltage remains the input and output variable. Taking into consideration the innate CF current tracking error, transfer function modifications owing to CF non-ideality are provided. Our theoretical analysis is confirmed by HSPICE simulation results with the CF block function implemented by a properly modified pure CMOS CCII. The proposed topologies, being able to realize high quality factor frequency responses obtainable by three CFs, constitute a good choice for trading off between the desired multiple character, the number of necessary active elements and a satisfactory performance.

Current-mode oscillators using single current follower

A new configuration for realising sinusoidal quadrature oscillators using current follower (CF) is presented. The effects of nonzero-offset voltage and current (at the input and output terminals of a current follower, respectively) on the oscillator are discussed. The resulting oscillating frequency is insensitive to the current tracking error of a CF. Simulation results which agree with theoretical analysis are obtained.