DC Charging Research Articles

Zero-Modulation Encoding in Magnetic Recording

This paper deals with waveform encoding methods in which binary data are mapped into constrained binary sequences for shaping the frequency spectrum of corresponding waveforms. Short and long pulse widths in the waveform are limited by constraints on the minimum and maximum run-lengths of zeros in the coded sequences. These constraints reduce the intersymbol interference in magnetic recording and provide an adequate rate of transition for accurate clocking. Signal power at low frequencies is limited by means of a constraint on a parameter that corresponds to the maximum imbalance in the number of positive and negative pulses of the waveform. This constraint on the maximum accumulated dc charge also eliminates the zero-frequency component. Zero modulation is one such code thati s especially suitable form agnetic recording channels. The encoding and decoding algorithm is presented, A one-to-one correspondence between binary data and constrained sequences is established by creating data states that are isomorphic to the charge states having the same growth rate. Sequences with other values of run-length and charge constraint are examined as candidates for other codes with zero dc component.

Codes for Self-clocking, AC-coupled Transmission: Aspects of Synthesis and Analysis

We consider NRZI waveform codes that satisfy a given set of run-length constraints and the upper bound on the accumulated dc charge of the waveform. These constraints enable the codeword to be self-clocking, ac-coupled, and suitable for data processing tape and communication applications. Various aspects of synthesis and analysis of such codes, called (d, k, C) codes, are illustrated by means of several examples. The choice of the initial state of the encoder is shown to influence the length of the data sequence over which the encoder must look-ahead.

Coaxial Marx-Bank Driver and Flashlamp for Optical Excitation of Organic Dye Lasers

A flashlamp pumped laser system that utilizes a coaxial Marx-Bank driver circuit is described. The property of the Marx-Bank circuit, which is to charge storage capacitors in parallel but discharge them in series connection, affords the practical advantage that high applied voltages and flashlamp input energies may be attained with a relatively low dc charging voltage. The use of a coaxial flashlamp and circuit configuration minimizes total inductance so that short duration, high energy pulses efficient for dye laser excitation are obtained.

Current Oscillations in Deep-level Doped Semiconductors

We observe current oscillations in p-i-n (and optically excited n-i-n) devices containing deep levels. The oscillations occur in the positive resistance region of the space-charge-limited (SCL) current regime of the I–V characteristics, before the occurrence of double-injection breakdown. This is a general effect, occurring in Si, Ge, and GaAs compensated with various deep-level impurities and in electron-irradiated devices. The oscillations are sinusoidal at threshold, with frequency strongly dependent on the recombination kinetics of the i-region, and on the deep level density, but are essentially independent of device length. The frequency and amplitude of the oscillations are affected by temperature and optical excitation. Various models have been proposed to account for oscillations in semiconductors containing deep levels, but no existing model describes fully the various aspects of the effect reported here. Because the device length exceeds carrier diffusion length, any model for the oscillation mechanism must include the existence of space charge and the kinetics of recombination, but may not depend essentially upon a traveling domain which imposes a length dependence on the oscillation frequency. Tentatively, we favor a model in which the recombination process unbalances the steady or dc space charge.

Electron Energy Distributions in Stationary Discharges

Calculations of the electron distribution function are presented for some simple examples of a stationary discharge in a dc space charge field. The treatment is valid when the predominant mechanism of energy exchange arises from motion in the dc space charge field. The computations indicate that the effect of dc space charge is, for a given external field strength, to increase the proportion of high energy electrons over that computed neglecting space charge. This results in a larger specific ionization rate, but the effect is not so great as to account for the low maintenance potentials observed in positive columns and in microwave discharges in inert gases.

An Impulse Generator-Electronic Switch for Visual Testing of Wide-Band Networks

The impulse generator-electronic switch is an instrument developed primarily to facilitate the design and production of radar networks such as delay, pulse-forming, and sweep networks. The instrument may be used to test any network that can be arranged to store a dc charge. Discharge characteristics of microsecond order, produced by a reference network and the network under test, are simultaneously displayed in pictorial form for comparative measurements. The first part of the paper describes representative applications and, with the aid of cathode-ray-oscilloscope traces, illustrates the simplicity of performance; the second part describes the circuit functions in detail.