Sitthichai Pookaiyaudom

A 3.3 volt high-frequency capacitorless electronically-tunable log-domain oscillator

A new type of electronically tunable oscillator using a cascade of two capacitorless first order log-domain all-pass filters as the frequency and the gain controlling element is proposed, where it is shown that the log-domain circuit technique is ideally suited for implementation of electronically tunable oscillators, The resulting oscillator enjoys several attractive properties, namely, low supply voltage, high oscillation frequencies, wide tuning range and relatively large oscillation levels can be obtained without excessive distortions, as oppose to previously reported forward-biased diode based electronically tunable oscillators.

Current-differencing band-pass filter realization with application to high-frequency electronically tunable low-supply-voltage current-mirror-only oscillator

A new method of realizing a band-pass filter by taking the difference between the outputs of two unequal bandwidth low-pass filters is proposed. The resulting band-pass filter is particularly suitable for implementation in current-mode forms. Such a current-differencing band-pass filter will then be applied to realize a new high-frequency, low-supply-voltage, current-mirror-only oscillator, possessing wide electronically tunable frequency range. A new simple and convenient loop-gain control method using the Early effect associated with the output transistors of the current-mirrors has also been employed to control the oscillation amplitude.

Log domain oscillators

Presents a new class of current-mode oscillators using several representative log-domain circuits both as the frequency and the gain controlling elements in electronically tunable oscillators, where the resulting oscillators enjoy the attractive properties of low supply voltages, high oscillation frequencies, wide tunable ranges and low distortion at large oscillation current amplitudes.

Understanding Wilson current mirror via the negative feedback approach

This paper presents a comprehensive study of a negative feedback mechanism in the bipolar Wilson current mirror, which is one of the most popular current mirrors used in electronic circuit designs. Although the operation of the Wilson current mirror has been covered in most microelectronic circuit design textbooks, its unusual negative feedback mechanism is still largely obscure. As a result, attempts to calculate the output resistance of the Wilson current mirror using classical negative feedback analysis have usually given the answer that is inconsistent with the correct answers obtained from direct analysis. We believe that this is probably the main reason why the negative feedback analysis of the Wilson current mirror is mostly ignored in the literature. In this paper, we aim to disclose the hidden subtleties of the Wilson current mirror by shedding a new light on its dual-loop negative feedback operation. It is shown in the paper that by doing so, we will be able to apply the negative feedback theory to the Wilson current mirror and correctly calculate its current gain and port resistances.

The active-R filter technique applied to current-feedback op-amps

The active-R filter technique attracted much interest in the 1970s as a method for implementing continuous-time analog filters. This technique used the internal capacitance of a voltage op-amp to derive the filter transfer function, and showed potential advantages in terms of high-frequency performance and IC integration. However the main disadvantages of the technique were found to be the strong temperature-dependence of the filter centre-frequency, and the limited dynamic range due to op-amp slew rate limitations. By applying the active-R technique to current-feedback op-amps, it is found that these major disadvantages are overcome. Thus the active-R technique applied to current-feedback op-amps seems a very promising method for the implementation of high-frequency integrated analog filter.

Automatic circuit simplification for meaningful symbolic analysis using the genetic algorithm

This paper demonstrates the use of the genetic algorithm to simplify both the final symbolic transfer functions and the initial equivalent circuits so that meaningful and understandable results can be obtained. The resulting simplified circuits are only as complicated as necessary to give the required accuracy in the results, which will also help in giving a better graphical insight into the circuits under consideration. This highly efficient algorithm has also been integrated into a symbolic circuit analysis package.

Transistor-level consideration of an RC current-mode oscillator using unity-gain current-mirrors

A new RC current-mode oscillator using unity-gain current-mirrors is presented. Transistor-level consideration in the analysis is needed to understand some important non-ideal circuit behaviours. The proposed oscillator shows good potential for wide tuning range and high-frequency operations. Frequency tuning can be done by varying only a single resistor.<<ETX>>

A Giga-Hertz-Range MOS Current-Tunable Sinusoidal Oscillator with Inherent Automatic Amplitude Control

A new all MOS current-mode current-tunable sinusoidal oscillator is proposed. Using a standard 0.8 μ CMOS fabrication process, an oscillation frequency of greater than 1 GHz can be achieved, with only 3.3 V supply voltage, and with less than 5–mW power consumption. Most importantly, a symmetrical automatic amplitude control or AGC function is also inherent in the circuit.

SUNRISE: the satellite UV NO-O2-O3 robust integrating spectrometer experiment

The satellite UV NO-O2-O3 robust integrating spectrometer experiment (SUNRISE) will develop highly sensitive spectrometers for satellite solar limb measurements. The first of our satellites will be launched in mid-2000, and will carry a test spectrometer called OPUS-1 which will accurately monitor the solar Lyman (alpha) during a period its normal coverage will be otherwise disrupted. It will be mounted alongside a series of more complex spectrometers, called OPUS-2 . . .. These will measure oxygen photolysis with the sun as an occulted UV light source. Inverse Abel transforms produce vertical target profiles in 3 km bins each sunrise and sunset. Our system can resolve the Schumann-Runge lines because we have devised ways to reduce greatly the systematic errors in our measurements with excellent systematic checks and system redundancies: Perhaps the most importantly, we get exoatmospheric spectra obtained immediately after sunrise and before sunset to give an excellent spectral calibration. We aim to measure O2 photolysis down to approximately 43 km. The SUNRISE collaboration has taken a fast, simple and robust route to the important measurements we have targeted. The satellites are in eccentric equatorial orbits at 800 km, with severe constraints on payload and power availability. The expected lifetimes of these satellites (8 - 15 years) offers unprecedented opportunities in UV-measurements and in ozone monitoring (for example, in spanning a sun-spot cycle) but places great demands on the robustness of our equipment. Our OPUS technology reflects that. Given that ozone has such a central role in atmospheric science, and that recent uncertainties (based on HALOE observations) in actual ozone deficits about 40 km have led to great uncertainties in atmospheric models, the precise measurement of O3 production and O3 sinks is very important. Our spectral range extends from 120 nm to 124 nm, in OPUS-1, and so we also will target the Lyman (alpha) line, which will allow real-time measurements of solar variability, and will in any case provide an excellent built in calibration, and 175 - 225 nm in OPUS-2. We can make significant measurements of NO absorption in the altitude range 40 km upwards with vertical resolution approximately 3 km and accuracies of approximately 10%. By establishing the levels of absorption in ozone, and comparing with the exoatmospheric measurements, we furthermore measure actual concentrations of ozone. SUNRISE therefore offers a unique tool making the simultaneous measurement of ozone production, concentrations, and a major mechanism of its loss, through the NO cycle. SUNRISE introduces an innovatory range of technologies, individually well-understood, the combination of which results in potentially large improvements in sensitivity and spectral selectivity.