K. Hayatleh

New current-mode precision rectifiers

Current-mode techniques are used to realize improved high-frequency precision full-wave rectifiers (PFWRs). Three alternative topologies are described and compared in performance with the classical operational amplifier (op-amp)/diode PFWR. These are a new op-amp supply current-sensing PFWR, a modified classical op-amp/diode design and a novel current-mirror feedback design. The latter exhibits good DC accuracy and the best frequency response.<<ETX>>

A novel bipolar-drive circuit for medical applications

A novel drive circuit, useful for medical electronics, is capable of supplying a sample of human tissue, across which there should be zero direct voltage (dc), with a well-defined test current from a source having an output impedance exceeding 16 MOmega at 100 kHz.

Design of amplifiers with high gain accuracy and high linearity

A novel amplifier design technique based on the negative impedance compensation is presented for amplifiers with feedback. The theoretical and simulation results have shown that the proposed technique is very effective and can provide high gain accuracy and high linearity with relatively low open-loop gain amplifiers, hence the technique has a very good potential for high frequency applications.

Critical review of the circuit architecture of CFOA

This study investigates the closed-loop performance of the basic current feedback operational amplifier (CFOA), with particular emphasis on its dynamic response. It also focuses on the design, performance and advantages of the CFOA in its ability to provide a substantially constant closed-loop bandwidth for closed-loop voltage gain. Furthermore, an improved CFOA with wide bandwidth and common-mode-rejection ratio (CMRR) performance is also presented. The design presented in this article uses a bootstrapping technique with Quasi-Darlington in the input stage to reduce the influence of the Early effect which results in improved performance. Another advantage of this design is that the inverting input impedance is reduced significantly, which leads to further improvement in bandwidth and CMRR.

High CMRR current-feedback operational amplifier

Despite excellent high frequency and high speed performance, current-feedback operational amplifiers (CFOAs) generally exhibit poor common-mode rejection properties, which limits their utility. In this paper the authors analyse the conventional (CFOA) in terms of common-mode rejection ratio (CMRR) performance, and, having identified the mechanism primarily responsible for the CMRR, they present a modified CFOA input stage circuit design by introducing a combination of a bootstrapping technique and folded cascode transistors. Simulation results of this new CFOA architecture indicate that the amplifier has significantly improved both CMRR and gain accuracy. Other key characteristics are also improved, with the notable exception of slew rate, which is reduced as a consequence of the new topology.

Novel high performance current-feedback op-amp

An improved current-feedback op-amp (CFOA) with good DC and CMRR performance is presented. Early-effects in the input stage of the conventional CFOA limit CMRR, PSRR and DC performance. The design presented here uses a bootstrapping technique with quasi-Darlingtons in the input stage to reduce the influence of the Early-effect resulting in improved performance. Another advantage of this design is that the inverting input impedance is reduced significantly which results in further improvements in the CMRR, the bandwidth and the input referred offset.

Self-Calibrating Infrared Thermometer for Low-Temperature Measurement

This paper presents a self-calibration technique for the removal of measurement errors caused by thermal gradients in thermopile-based infrared thermometry, particularly when measuring low temperatures. Applications for this self-calibration method include low-temperature measurement in the food industry and infrared thermometers for remote temperature monitoring in cold climates. The self-calibration technique reported in this paper is shown to reduce the measurement error to within ±1°C within 5 s of an extreme thermal shock, compared with an uncompensated thermometer that does not recover until the thermal gradient is removed. The root-mean-square temperature noise for the duration of the thermal shock test is less than 0.2°C. This technique is the subject of a patent application and can be applied to any infrared thermometer utilizing a thermopile, regardless of the thermopile size and geometry.

High frequency performance of current-mode precision full wave rectifiers

The current-mode topology reported by Hayatleh et al. [1993] provides an improved high frequency performance over the traditional design, but the circuit response still begins to degrade significantly at-about GB/100, where GB is the gain-bandwidth of the op-amps being used. Detailed investigation of the principal degradation mechanisms has been undertaken and from the results of this study two main causes for the non-ideal performance have been identified. Even though the work reported here is specifically related to the PFWR, these two-mechanisms responsible for degrading the performance at high frequencies also apply in part to all PFWR and a wide number of circuits that employ opamp/diode feedback structures.<<ETX>>

A novel current-feedback op-amp exploiting bootstrapping techniques

The operation of the conventional current feedback operational amplifier (CFOA) is reviewed and its performance parameters used as benchmarks in the development of a new input stage architecture that provides a common-mode rejection ratio (CMRR) improvement of some 45 dB and offset voltage less than 10 mV.

A wide bandwidth voltage-follower with low distortion and high slew rate

A symmetrical BJT voltage-follower is presented which combines low harmonic distortion and high slew rate. Unlike conventional class-AB voltage-followers the proposed design provides large signal swing, some plusmn4.5 V on a plusmn5 V power supply, as well as large positive and negative output currents for driving capacitive loads, resulting in high slew-rate capability. The circuit exhibits gain flatness of 0.1 dB at 728 MHz with an inductive behaviour coming in at higher frequencies. The operational range is -20degC to +100degC with a power consumption of 55 mW at room temperature.