Current Feedback Technique Research Articles

A CMOS IC for portable EEG acquisition systems

We present a monolithic low-power, low-noise analog front-end electroencephalogram acquisition system. It draws only 500 /spl mu/A from a standard 9-V battery, making it suitable for use in portable systems. Although fabricated in a standard CMOS technology, by using current feedback techniques it achieves a common mode rejection ratio of 100 dB while the total input noise referred to input is kept below 1.5 /spl mu/V (rms).

A CMOS micropower input amplifier for hearing aids

This paper describes a CMOS input amplifier for integrated circuits in hearing aids. It has a differential-input differential-output topology, which allows direct driving of cascaded fully-differential processing stages. The adoption of the voltage-to-current conversion and current feedback technique in the amplifying structure, together with the use of a simple differential stage in the offset reduction and in the common-mode feedback loops, allows micropower consumption to be achieved. Experimental results show very good noise and total harmonic distortion performance.

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 Ω. At the same time, the dc parameters that are the traditional problems of the current-feedback amplifiers are improved to be around 25 μV 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.

On the design of low-noise current-mode optical preamplifiers

Classical designs of optical transimpedance amplifiers for p-i-n photodiode receiver circuits generally employ common-emitter or common-source input stages. In this paper we explore the design of a new class of low-noise “current-mode” optical preamplifier based upon common-base and common-gate input stages. Two current-mode designs are considered, firstly an improved bipolar common-base configuration and secondly a GaAs MESFET common-gate configuration. Both designs employ current-feedback techniques to achieve higher transimpedance gains than is obtained with classical voltage-feedback structures for the same operating bandwidth. A theoretical noise analysis of the new current-mode designs confirms the expected low noise performance. Finally, experimental noise measurements at 100-MHz bandwidth indicates that under certain conditions electrical noise improvements of up to 4 dBs over classical designs can be obtained with the new current-mode circuits.

New improved modulation method for a cycloconvertor driving an induction motor

This paper describes new modulation techniques that remove all the major limitations of the noncirculating current cycloconvertor, including low maximum frequency, subharmonics, poor bank crossover timing, and distortion due to discontinuous current, when used to drive an induction motor. The new modulation techniques work by keeping the flux in the induction motor (sensed by voltage feedback) as close to sinusoidal as possible and give superior performance to the present current feedback techniques. An experimental 18-thyristor 3-pulse cycloconvertor showed that the new modulation techniques allow smooth speed control of an induction motor from 0 to 25 Hz (limited by software) with a peak output voltage of 95% of the input voltage. It is expected that the same techniques applied to a 36-thyristor 6-pulse cycloconvertor will allow smooth speed control up to 50 Hz. To obtain fast speed response, vector control can be easily added to the new modulation techniques. The new modulation techniques can also be used to advantage in other cycloconvertor and convertor applications. Patents have been applied for.

Optical frequency stabilisation and line width reduction of a multielectrode DFB laser with current feedback

Optical frequency stabilisation and linewidth reduction by the current feedback technique were studied with a multi-electrode DFB laser. In the current feedback technique, phase rotation in the feedback loop, particularly induced by a laser, is the fundamental problem. This problem was resolved by using multielectrode DFB lasers without phase inversion. We simultaneously succeeded in optical frequency stabilisation and linewidth reduction with only one feedback electrical circuit. Optical frequency drift and spectral line-width were reduced to 1/14 and 1/126, respectively, of those in the free-running state. The minimum spectral linewidth obtained was 95 kHz.

Optical frequency scanning of a stabilised and linewidth-reduced multielectrode DFB laser using current feedback

Optical frequency scanning of a stabilised and linewidth-reduced multielectrode DFB laser has been demonstrated using a current feedback technique. The scanning range of the linewidth-reduced multielectrode DFB laser was 4Å (50 GHz) and 9Å (120 GHz) when the linewidth was reduced to 1/50 and 1/20, respectively, of that of a free-running state laser.