Design of a CMOS Compatible CFOA and its Application in Analog Filtering

It is presented the design of a current-feedback operational amplifier (CFOA) which is suitable for implementation with standard CMOS integratedcircuit technology of 0.35µm. The characteristics of the CFOA are derived by using biases of ±2.5V and Ibias=20µA. The usefulness of the CFOA is demonstrated by designing mixed-mode biquads which realize the low-pass, high-pass, band-pass, notch and all-pass filter functions. As a result, it is highlighted that the SPICE simulations of the biquad working in voltage-mode are in good agreement with the biquad working in current-mode.     

High-performance active bandpass filter using current-feedback amplifiers

An accurate current feedback amplifier based high-Q active bandpass filter whose centre frequency is independently variable over a wide frequency range is presented. The basic circuit has the important advantage that access to the Z node of the current-feedback amplifier is not required, as is the case with many existing current-feedback amplifier filter circuits. Additionally, the circuit can be implemented with operational amplifiers, though for high Q the Q? and ω₀? variabilities are 62% better with current-feedback amplifiers than with operational amplifiers. Experimental results are presented which are in good agreement with expected theory.     

Multi-function biquad using single current differencing transconductance amplifier

An universal multi input single output type multifunction biquad is proposed. The proposed configuration employs only one current differencing transconductance amplifier as the active element, two capacitors and three resistors. The circuit realizes all five filter functions (i.e. Low Pass, High Pass, Band Pass, Notch and All Pass) without changing the circuit topology. The natural frequency ω₀ is independently and electronically tunable. The workability of the proposed multifunction biquad has been verified using SPICE simulation.     

Universal current-mode biquad filter using dual output current differencing transconductance amplifier

A new universal current-mode biquad filter using current differencing transconductance amplifier (CDTA) is proposed. The proposed configuration can realize the second-order low pass, high pass, band pass, and band reject responses simultaneously. The circuit employs both grounded capacitors (ideal for integrated circuit implementation), and offers low active and passive sensitivities. The workability of the proposed configuration has been verified using SPICE simulation.     

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.     

Temperature compensated logarithmic peak detector

A temperature compensated logarithmic amplifier for signal strength indicator or automatic gain control applications is presented. The logarithmic function is realized with a current-feedback operational amplifier with a nonlinear diode feedback. The designed BiCMOS current-feedback operational amplifier utilizes a novel circuit topology which makes possible constant 1 MHz bandwidth amplification with closed loop voltage gains up to 60 dB. The offset current of the current-feedback amplifier is cancelled with an active OTA-C feedback loop. The logarithmically amplified signal is further processed by a peak detector and a temperature compensation circuit. The temperature compensation principle is based on a division of two v _BE:s and it is realized with a current controlled variable current mirror. The logarithmic amplifier is fabricated with a 1.2 micron BiCMOS-process with NPN's f_T of 7 GHz. The power consumption of the circuit is 25 mW with a 4.5 V supply voltage.     

A composite approach for improving the DC performances of current-feedback amplifiers

A new approach for improving the performances of the increasingly popular current-feedback amplifiers is proposed. It utilizes the composite amplifier concept to null out the offset voltage and input bias current of the amplifier while the current-feedback technique is used to improve the ac performances of the overall amplification block. The new proposal is verified by extensive simulations and a prototype is also constructed. The fabricated amplifier presents excellent ac performances, such as 250-MHz bandwidth, 2.8-ns rise-time with 10-Vp-p swing, and a settling time of 19 ns to 0.1% and 25 ns to 0.02% with 10-Vp-p swing, all on a load of 100 . At the same time, the dc parameters that are the traditional problems of the current-feedback amplifiers are improved to be around 25 V offset voltage and 500-nA input bias current. The paper also presents an evaluation of the other techniques that are recently proposed to improve the dc performances of the current-feedback amplifiers so that a comparison can easily be made between the new approach and the other approaches. Both simulation results and measurements from the prototype are included in this paper.     

Second-order OTA-C filters derived from Nawrocki-Klein biquad

Based on the Nawrocki and Klein biquad and using different input and output techniques, many new filter structures and functions are developed from both voltage- and current-mode viewpoints. For example, it is found that the basic five operational transconductance amplifier (OTA) structure has the LP, BP, HP, BS and AP functions without the use of capacitor injection and component matching, a feature shared by no other existing two integrator loop OTA-capacitor (OTA-C) circuit, including the original NK biquad. Various BS, LPN, HPN, AP and universal architectures are obtained, which require fewer OTAs and may be more useful than the original biquad. This research shows that the NK biquad is one of the most important second-order OTA-C filters at least from the viewpoint of filter architectures and functions, and thus should receive attention in continuous-time filter design     

New current-feedback amplifier configuration

Current-feedback amplifiers are increasingly being used, particularly because of their near gain-independent bandwidth property, but the variety of current-feedback amplifiers is somewhat limited. This paper describes a new current-feedback amplifier configuration that utilizes a voltage amplifier in conjunction with a current conveyor in an unconventional manner, and is particularly suited for low-voltage CMOS implementation. A complete analysis is given, and experimental results using a variety of commercial devices confirm the validity of the proposed design.     

Voltage-Mode New Universal Biquad Filter Configuration Using a Single VDIBA

A universal voltage-mode filter configuration employing a voltage differencing inverting buffered amplifier (VDIBA), two capacitors and a resistor is proposed. The presented structure can realize all the five standard biquadratic filters: low-pass, high-pass, band-pass, band-reject and all-pass, without changing the circuit topology. The proposed filter circuit also provides the following advantageous features, not available simultaneously in any of the single active element/device based universal biquad realizing all the five filter responses known earlier so far: (i) independent electronic tuning of natural angular frequency (ω ₀) and bandwidth (BW), (ii) no requirement of any element matching condition or inversion of input signal(s) (as needed in most of the earlier reported structures), and (iii) low active and passive sensitivities. Moreover, even the internal structure of the new building block is possibly the simplest among all recently introduced new building blocks. The workability of the proposed filter has been confirmed by SPICE simulations using 0.18 μm technology.     

New voltage-model/current-mode universal biquad filter using unity-gain cells

A new universal biquad filter is presented which can realize all the five standard filter functions namely lowpass, bandpass, highpass, notch and allpass in voltage-mode (VM) as well as in current-mode (CM) employing only unity-gain cells (i.e. voltage followers and current followers) as active elements. Explicit VM/CM outputs are available from low output impedance terminals and high output impedance terminals, respectively. The workability of the proposed universal biquad, realized with CMOS unity-gain cells, is established by SPICE simulations.     

CMOS current-controlled current differencing transconductance amplifier and applications to analog signal processing

This article presents design of a basic current-mode building block for analog signal processing, named as current-controlled current differencing transconductance amplifier (CCCDTA). Its parasitic resistances at two current input ports can be controlled by an input bias current. Owing to working in current-mode of all terminals, it is very suitable to use in a current-mode signal processing, which is continually more popular than a voltage one. The proposed element is realized in a CMOS technology and is examined the performance through PSPICE simulations. They display usability of the new active element, where the maximum bandwidth is 311 MHz. The CMOS CCCDTA performs low power consumption and tuning over a wide current range. In addition, some examples as a current-mode universal biquad filter, floating inductance simulator and quadrature oscillator are included. They occupy only single CCCDTA.     

Three-input single-output second-order filters using current-feedback amplifiers

In this study, a novel second order universal filter using current-feedback amplifier, commercially available active component, is presented. The signal-flow graph method is used to synthesize the filter. The proposed filter has three high impedance input and one output, (multiple input single output (MISO) configuration). It can generate all biquadratic filtering functions namely: low-pass (LP), band-pass (BP), high-pass (HP), band-reject (BR) and all-pass (AP) at the output terminal by selecting different input signal combinations. The validity of the proposed circuits is demonstrated by simulations.     

Single CCII-based voltage-mode universal filter

A new voltage-mode universal biquad filter is presented which can realize all the five standard filter functions namely lowpass, bandpass, highpass, notch, and allpass employing only one CCII as active element. The new circuit is composed of only one CCII, two capacitors, and three resistors, and realizes five generic filter signals without any inverting-type voltage input signals. This is unlike biquad reported by filter structures which employs more active components and needed an inverting-type voltage input signal to realize allpass signal.     

Cascadable Current-Mode Biquad Filter and Quadrature Oscillator Using DO-CCCIIs and OTA

This article introduces a circuit which can function both as a quadrature oscillator and as a universal biquad filter (lowpass, highpass, bandpass). When the circuit functions as a universal biquad filter, the quality factor and pole frequency can be tuned orthogonally via the input bias currents. When it functions as a quadrature oscillator, the oscillation condition and oscillation frequency can be adjusted independently by the input bias currents. The proposed circuit can work as either a quadrature oscillator or a biquad filter without changing the circuit topology. The amplitude of the proposed oscillator can be independently controlled via the input bias currents. The proposed oscillator can be applied to provide amplitude modulated/amplitude shift keyed signals with the above-mentioned major advantages. The circuit is very simple, consisting of four dual-output second generation current controlled current conveyors (DO-CCCIIs), one operational transconductance amplifier (OTA), and two grounded capacitors. Without any external resistors and using only grounded elements, this circuit is therefore suitable for IC architecture. PSPICE simulation results are depicted here, and the given results agree well with the theoretical analysis. The power consumption is approximately 7.32 mW at ±2.5 V supply voltages.     

Universal filter using two current-feedback amplifiers

A new universal filter using two current-feedback amplifiers is presented. This filter can realise lowpass, bandpass, highpass, notch and allpass filters from the same configuration. It has the following features: orthogonal control of the natural frequency and quality factor by grounded resistors, easy conversion into a voltage-controlled filter, minimum active components, without match components except for allpass applications, low active and passive sensitivities, and cascadability. Experimental results that confirm the theoretical analyses are obtained     

Analytical Synthesis of the Digitally Programmable Voltage-Mode OTA-C Universal Biquad

None of the recently reported voltage-mode versatile filters are digitally programmable for applications like the easy addition of current-mode filtering signals to do the synthesis. None of the recently reported analytical synthesis methods are used for the realization of a multifunction filter. Both the above two induced motivations of researches have been merged, developed, and solved in this brief on the voltage-mode operational transconductance amplifier (OTA)-C universal biquad filter, which still achieves many advantages like the employment of all single-ended-input OTAs, all grounded capacitors, and the least number of active transistor and passive component counts, in addition to having a controllable gain, a cascadable input terminal, and the absence of the need to impose component matchings.     

Voltage mode universal filters employing single FDCCII

In this paper, four new voltage-mode universal biquad filters configuration are proposed. First of two circuits proposed high-input impedance universal filter with single-input and three-outputs, which can simultaneously realize voltage mode low-pass, band-pass and high-pass filter responses employing all grounded passive components. The third proposed universal filter three-input and single-output, which also can realize all the standard filter functions. The fourth circuit proposed universal filter with three-input and five-outputs, which can be used as either a three-inputs single-output or a two-inputs five-outputs universal filters. It can realize all five different generic filtering signals: low-pass, band-pass, high-pass, band-stop and all-pass. Simulation results are given to confirm the theoretical analysis. The proposed biquad filters are simulated using TSMC CMOS 0.35 μm technology.     

THE DESIGN OF ACTIVE CURRENT-MODE FILTER WITH STATE VARIABLE METHOD

Basing on the state variable method, a block diagram of the current-mode biquad active circuit was proposed, whose integrators were realized using three kinds of active elements such as operational amplifier, second generation current conveyors and operational transconduc-tance amplifiers-electric capacity. The characteristics of each circuit were analyzed.     

基于电流反馈运算放大器的R-L和C-D阻抗的实现和应用

在集成电路的设计中,电感的集成是很困难的,因此,用有源电路来模拟电感很有必要。目前通用的做法是用电流传送器等有源器件实现的RL/CD阻抗电路,但基于电流反馈运算放大器实现的RL/CD阻抗电路却很少。结合相关的研究进展,用电流反馈运算放大器和一些无源元件实现了R-L(电阻-电感)和C-D(电容-频变负阻)系列阻抗电路。并且用该电路能实现高通?低通和高通滤波器功能。