Log Amp Research Articles

Sub-microsecond wavelength stabilization of tunable lasers with the internal wavelength locker

We proposed a method of accelerating the wavelength stabilization after wavelength switching of the tunable distributed amplification-distributed feedback (TDA-DFB) laser using the internal wavelength locker to reduce the size and the cost of the wavelength control system. The configuration of the wavelength stabilization system based on this locker was as follows. At the wavelength locker, the light intensity after an optical filter is detected as a current by the photodiodes (PDs). Then, for estimating the wavelength, the current is processed by the current/voltage-converting circuit (IVC), logarithm amplifier (Log Amp) and field programmable gate array (FPGA). Finally, the laser current is tuned to the desired wavelength with reference to the estimated wavelength. With this control system the wavelength is stabilized within 800 ns after wavelength switching, which is even faster than that with the conventional control system.

IEEE Journal of Solid State Circuits: The Evolution and Future of This Flagship Publication

In 1966, the first and the second issues of IEEE Journal of Solid-State Circuits (JSSC) were published in September and December. The articles in these issues were expanded versions of papers from the 1966 International Solid-State Circuits Conference (ISSCC) [1]. The articles were written by groups of authors from companies and universities in the United States. A large number of the papers described various bipolar amplifiers with low-drift, wideband, band-pass, low-power, and frequency selective features; oscillators; and the differential sense amplifier for ferrite memory. The performance of NMOS versus bipolar transistors at very high frequencies and a tunnel diode log amp were also described. Digital and memory papers were also included, such as the bipolar OR logic, current mode switch, selection circuitry for magnetic thin-film memory, and MOS adaptive memory. Functional electronic linear IC blocks for the Apollo Lunar Excursion Module television camera was also described.

A flow cytometer designed for fluorescence calibration.

In the development of suitable standards and calibration materials for fluorescence measurement, it becomes necessary to make accurate fluorescence measurements of these materials on flow cytometers. The results of such measurements may be affected by numerous sources of error, prominent among which are deviations of logarithmic amplifiers (log amps) from ideal response. To minimize the deleterious effects of log amps and multicolor fluorescence compensation circuitry on measurements, we built a flow cytometer with electronics incorporating high-precision peak detectors usable over a range from below 2 mV to 10 V, and we developed data acquisition software that transfers held peak values to a commercial 16-bit data acquisition system mounted in a personal computer running Windows 95. Fluorescence compensation is done in software, and transformation of the compensated data from a 16-bit linear to an 8-bit, 4-decade logarithmic scale is accomplished using a look-up table. Although dynamic range may be restricted by noise in the data acquisition system, high sensitivity can be achieved by photomultiplier tube gain adjustment, and it is likely that the use of a lower noise data acquisition system and/or digital processing of pulse information will enable operation over the full 4-decade dynamic range. Even at its current performance level, our instrument provides substantially better linearity over most of the scale than can be obtained using conventional electronics incorporating log amps; we believe this characteristic is critical for use in standards development.

Logarithmic amplifiers

Logarithmic amplifiers (log amps), which produce an output signal proportional to the logarithm of the input signal, are widely used in cytometry for measurements of parameters that vary over a wide dynamic range, e.g., cell surface immunofluorescence. Existing log amp circuits all deviate to some extent from ideal performance with respect to dynamic range and fidelity to the logarithmic curve; accuracy in quantitative analysis using log amps therefore requires that log amps be individually calibrated. However, accuracy and precision may be limited by photon statistics and system noise when very low level input signals are encountered.

High-performance GaAs heterojunction bipolar transistor monolithic logarithmic IF amplifiers

Logarithmic IF amplifiers that implement both true and successive-detection designs are reported. Monolithically cascaded log gain stages are used to achieve piecewise-approximated logarithmic functions for the compression of signals over a wide dynamic range. The heterojunction bipolar transistor (HBT) IC fabrication process is based on a 3- mu m-emitter, self-aligned-base ohmic metal transistor using both molecular-beam epitaxy (MBE) and metal-organic metal vapor deposition (MOCVD) growth structures. The true log amp integrates four dual-gain (limiting and unity gain) stages without on-chip video detection. Its performance includes DC-3-GHz IF/video bandwidth, 400-ps rise time, <+or-dB log error over approximately=40-dB dynamic range at 3 GHz, and a tangential signal sensitivity (noise) of -60 dBm (test-set limited). The successive-detection log amp, designed for lower frequency and dynamic range applications, uses three limiting gain stages and four detector stages to achieve a 550-MHz bandwidth and <-0.34-dB log error over a 27-dB dynamic range. It is able to process 13-ns pulses with 5.0-ns and 5.2-ns risetimes and fall times, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>