Spl Radic Research Articles

A 16-channel charge sensitive amplifier IC for a PIN photodiode array based PET detector module

A 16-channel integrated circuit charge sensitive preamplifier has been developed for a PET detector module that uses an 8/spl times/8 array of PIN photodiodes to identify the crystal of interaction. The amplifier, which is made using 1.2 /spl mu/m CMOS technology, produces an output of 100 mV per 1000 e/sup -/ input, and its noise performance is optimized for 10 pF detector capacitance. The rise time, fall time, bias current through the first FET, and detector current compensation are each controlled by a dc current applied to the 2 mm square chip. The Johnson noise (e/sup -/ fwhm at 1 /spl mu/s peaking time) is 173+13C, where C is the input capacitance in pF, and the shot noise (e/sup -/ fwhm) is 16.4/spl radic/(IT), where I is the detector dark current in pA and T is the amplifier shaping time in /spl mu/s. With this amplifier, the target noise of 300 e/sup -/ fwhm can nearly be met with 300 /spl mu/m depletion thickness photodiodes (3 pF, 200 pA per 3/spl times/3 mm element). >

False alarm analysis of the envelope detection GO-CFAR processor

The greatest of constant false alarm rate processor (GO CFAR) is a useful architecture for adaptively setting a radar detection threshold in the presence of clutter edges. The GO CFAR input is often the envelope detected in-phase (I) and quadrature (Q) channels of the baseband signal (x/sub e/=/spl radic/(I/sup 2/+Q/sup 2/)). This envelope detection can also be approximated using x=a max{|I|,|Q|}+b min{|I|,|Q|} which requires less complex hardware (a and b are simple multiplying coefficients). The envelope GO CFAR processor and several envelope approximation GO CFAR processors are compared in terms of the probability of false alarm (PFA) performance. Closed-form expressions which describe the PFA performance are given and their accuracy evaluated. It is shown that for all cases, the PFA is proportional to the number of reference cells n for small threshold multiplier T and inversely proportional to n for large T. A region of intersection occurs where the PFA is the same for two different values of n. For example, at T'=1.68 in the |I|+|Q| GO CFAR (a=1, b=1) the PFA for n=1 is equal to the optimal n=/spl infin/ fixed-threshold PFA (PFA=0.112).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design of efficient balanced codes

All words in a balanced code have equal number of ones and zeros. Denote by DC(n,k) a balanced (or dc-free) code of length n, and 2/sup k/ code words. We design an efficient DC(k+r, k) code with k=2/sup r+1//spl minus/0.8/spl radic/(r/spl minus/2). These codes are optimal up to the construction method, introduced by D.E. Knuth (1986). >

Asymptotic bounds on optimal noisy channel quantization via random coding

Asymptotically optimal zero-delay vector quantization in the presence of channel noise is studied using random coding techniques. First, an upper bound is derived for the average rth-power distortion of channel optimized k-dimensional vector quantization at transmission rate R on a binary symmetric channel with bit error probability /spl epsiv/. The upper bound asymptotically equals 2/sup -rRg(/spl epsiv/,k,r/). where k/(k +r) [1 - log/sub 2/(l +2/spl radic/(/spl epsiv/(1-/spl epsiv/))] /spl les/g(/spl epsiv/,k,r)/spl les/1) for all /spl epsiv//spl ges/0, lim/sub /spl epsiv//spl rarr/0/g(/spl epsiv/,k,r)=1, and lim/sub k/spl rarr//spl infin//g(/spl epsiv/,k,r)=1. Numerical computations of g(/spl epsiv/,k,r) are also given. This result is analogous to Zador's (1982) asymptotic distortion rate of 2/sup -rR/ for quantization on noiseless channels. Next, using a random coding argument on nonredundant index assignments, a useful upper bound is derived in terms of point density functions, on the minimum mean squared error of high resolution, regular, vector quantizers in the presence of channel noise. The formula provides an accurate approximation to the distortion of a noisy channel quantizer whose codebook is arbitrarily ordered. Finally, it is shown that the minimum mean squared distortion of a regular, noisy channel VQ with a randomized nonredundant index assignment, is, in probability, asymptotically bounded away from zero. >

New View on an Anisotropic Medium and Its Application to Transformation from Anisotropic to Isotropic Problems

The metric factor is defined as m(epsilon*/sub x/, epsilon*/sub y/, theta/sub x/) = /spl radic/ cos/sup 2/theta/sub x/ / epsilon*/sub x/ + sin/sup 2/theta/sub x/ / epsilon*/sub y/ in the radial direction, with the angle theta/sub x/ from the x axis being one of the principal axes in an anisotropic dielectric medium filling the two-dimensional space. The normalized metric factor is defined as n(epsilon*/sub x/, epsilon*/sub y/, theta/sub x/, beta) /spl equiv/ m(epsilon*/sub x/, epsilon*/sub y/, theta/sub x/) / m(epsilon*/sub x/, epsilon*/sub y/, beta) in the form normalized by the metric factor in the direction with the angle beta from the x axis. The effective path length d'/sub P1P2/ between the points P1 and P2 is defined as d'/sup P1P2/ = n(epsilon*/sub x/, epsilon*/sub y/, theta/sub x/, beta)d/sub P1P2/ where d/sub P1P2/ is the actual path length of the straight line P1P2 with the angle theta/sub x/ from the x axis. We propose the minimun principle of the effective path length for electric flux in the region with multilayered anisotropic media. It is applied to solving the electrostatic problem with two anisotropic media whose principal axes are different. We show by using the normalized metric factor that the anisotropic problem can be transformed into the isotropic problem.

On the Theory and Application of the Dielectric Post Resonator (Short Papers)

This short paper deals with the modes of the dielectric post resonator when epsilon/sub r/ is large. The normalized frequency F/sub 0/ = (pi D/lambda/sub 0/) /spl radic/ as a function of D/L is discussed. The simple approximate expressions for the resonant frequencies of the lower order modes are given. The properties of the TE/sub 011/, mode are discussed in detail from the point of view of its application to the measurement of the complex permittivity of microwave dielectrics. Curves and expressions for fast and simple determination of the maximum measurement errors are given.