Passive Delay Research Articles

A new generalized cross correlator

A new generalized cross correlator (GCC) for the passive time delay estimation problem is presented. The interpretation of this GCC is that of estimating the cross-correlation function by cross correlating the least mean-square estimates of the signal component in each of the observed waveforms. The implementation is simply a GCC with the weighting filter equal to the magnitude coherency squared. Numerical evaluation of the performance of this processor and a robust version indicate that they compare favorably to some of the well-known GCC procedures.

Fundamental limitations in passive time-delay estimation--Part II: Wide-band systems

This is the second part of a study which deals with the problem of passive time delay estimation. The focus here is on systems employing wide-band signals and/or arrays of very widely separated receivers. A modified (improved) version of the Ziv-Zakai lower bound (ZZLB) is used to analyze the effect of additive noise and signal ambiguities on the attainable mean-square estimation errors. When the lower bound is plotted as a function of signal-to-noise ratio (SNR), one observes two distinct threshold phenomena dividing the SNR domain into three disjointed segments. At high SNR, the lower bound coincides with the Cramér-Rao lower bound (CRLB). This is the ambiguity-free mode of operation where differential delay estimation is subject only to local errors. At moderate SNR (between the two thresholds), the lower bound exceeds the CRLB by a factor of 12(ω <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> /w) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\omega_{0}</tex> and w are, respectively, the center frequency and signal bandwidth. In this region, the ambiguities in the received signal phases cannot be resolved; however, a useful estimate of the differential delay can still be obtained using the received signal envelopes. At low SNR, the lower bound approaches a constant level depending only on the a priori search domain of the unknown delay parameter. In this region, signal observations are subject to envelope ambiguities as well, and are thus essentially useless for the delay estimation.

Optical systems and sensors for measurement and control

The author discusses the future roles of optical fibre systems in instrumentation and draws attention to some of the potential areas in which current developments in opto-electronics may well considerably expand the applications arena. The major possibilities include the all optical sensor and actuator system, the incorporation of passive signal processing, analogue-to-digital conversion and passive delay line multiplexing, and the impact of advanced optical technology including single mode optics and integrated optic concepts. Some potential systems are described which illustrate the considerably increased role for optical techniques in instrumentation.

Multigigahertz-bandwidth linear-frequency-modulated filters using a superconductive stripline

Superconducting niobium patterned to form strip transmission lines on sapphire and silicon dielectric substrates has been used to make passive delay lines, capacitively coupled resonators, and linear-FM chirp filters. Chirp filters with a 37.5-ns dispersion and 2.3-GHz bandwidth were implemented by nonuniformly tapping nondispersive delay lines using proximity directional couplers. Pulse compression tests using two complementary filters agree well with theory. The results demonstrate a technology which promises to provide analog signal processing with about an order of magnitude bandwidth increase over surface-acoustic-wave and acousto-optic devices.

Networks for annulling gain and delay inequalities

Descriptions are given of passive even-echo-pair and odd-echo-pair networks suitable for the separate annulling of chrominance-luminance gain and delay inequalities arising in television links. Both circuits are constructed by modifying a passive lumped-element delay section.

A complementary driver with a subnanosecond rise time

A circuit specifically designed as a complementary driver for a high- speed scaling circuit is described. This circuit incorporates the principle of time-delayed negative feedback by using a passive delay line in the feedback path. The delay line provides optimum positioning of the bias voltage at the base of the nondriven transistor in a current-mode pair.