Leonard Hayden

Characterization and modeling of multiple line interconnections from time domain measurements

Methods have been developed to extract electrical circuit models from time domain measurements of lossless, nonuniform, multiconductor transmission lines for two broad classes of structures. Although unique solutions are not feasible for general structures that scatter the propagating wave-front, approximate solutions have been identified. For the first class of structures a single velocity wave-front is assumed, equivalent to the homogeneous media case. The second class is for structures with identical lines, such as a parallel line bus structure, where separable modal wave-fronts propagate. For these cases the propagation behavior (eigenvector matrix) is determined only by the known number of lines, N, allowing decoupling of the system into N orthogonal modal transmission lines. Circuit models have been developed for these decoupled nonuniform lines, as well as for the equal modal velocity assumption which relies on a matrix impedance profile to fully describe the system. >

An enhanced Line-Reflect-Reflect-Match calibration

This paper reports the results of a detailed study of a commercial implementation of the Line-Reflect-Reflect Match (LRRM) vector network analyzer calibration method with automatic load inductance correction. Limitations in applicability for non-offset standards and when the Line (Thru) standard is electrically long and/or the load inductive reactance is large are examined. An enhanced LRRM (eLRRM) algorithm has been developed providing superior and more predictable results for these less frequently encountered cases. eLRRM is available in a commercial VNA calibration software product.

Sensitivity Analysis of Calibration Standards for SOLT and LRRM

We investigate the sensitivity of SOLT and LRRM on wafer calibrations to probe positioning. Calibration comparison derived error-bounds were calculated for data sets differing only by a single change in probe/standard overlap. The SOLT calibration was found to be significantly more sensitive to probe placement variations, consistent with theoretical predictions.

A New Characterization and Calibration Method for 3-dB-Coupled On-Wafer Measurements

A two-port vector network analyzer (VNA) can be used for measuring the differential-mode (or common-mode) S-parameters of an integrated circuit by combining on-wafer probes with 3-dB-coupling baluns (or power splitters). In such a measurement setup, the error networks from each port of the VNA to the device-under-test are three-port rather than the conventional two-port. This paper proposes a new set of an impedance standards and algorithm that can efficiently extract the full nine mixed-mode S-parameters of the three-port error network. For differential-mode measurements, the four differential-mode S-parameters are used for the calibration and the remaining five common- and cross-mode S-parameters are used for evaluating their associated measurement errors. By a minor variation, the proposed method can be used for characterizing the full nine mixed-mode S-parameters of the 3-dB-coupler embedded probe itself, providing a valuable tool in its development stage. The proposed method uses a pseudoinverse of an overdetermined matrix, by which it becomes tolerant to errors that occur when measuring the impedance standards.

A probe technology for 110+ ghz integrated circuits with aluminum pads

There is a growing interest in probing Si-based RFICs and test structures with aluminum pads. Probing RFICs with aluminum pads is significantly more difficult than probing ICs with gold pads. This is because a thin layer of aluminum oxide (about 60 angstroms thick) naturally forms on the aluminum surface that impairs the electrical contact between the tips of the probes and the aluminum pads. Any measurement that is sensitive to a series resistance will be affected by contact resistance variations. Such measurements include inductor Q measurements and long characterization tests that require repeatable device contact for time periods beyond a few minutes (Schreurs, 2001). Conventional probes use tungsten tips to penetrate the aluminum oxide layer. Unfortunately, the tungsten itself also oxidizes and the aluminum oxide, after only a few contacts, accumulates on the tips of the probes, significantly increasing the contact resistance and hence resulting in measurement deterioration (Kister, 1998). As a remedy, frequent cleaning of the probe tips is obligatory. Worse, the operator is usually unsure of the precision of the measurements, due to the non-repeatable nature of the contact resistance. Recently probe card developments based on polyimide membrane technology showed superior performance on aluminum pads (Smith, 1999). In this paper, and based on this technology, we present a new single-port RF probe for aluminum pads that has a superior performance compared to conventional probes

VNA error model conversion for N-port calibration comparison

This paper examines the extended 12-term error model commonly used in commercial multiport vector network analyzers, introduces a generalized multiport error model, and applies this error model for the purposes of general N-port comparison of calibrations. These tools have been implemented in a commercially available calibration and measurement software product. Previous work demonstrated the utility of these tools in the estimation of calibration error associated with ignoring coupling and for evaluating measurement system repeatability. Equations are presented for bidirectional conversion between an extended 16-term-like error model and the extended 12-term model as well as for calculation of DUT-specific and worst-case multiport calibration comparison error bounds.

Effect of a Local Ground and Probe Radiation on the Microwave Characterization of Integrated Inductors

Microwave characterization of an integrated inductor is often carried out with respect to a local ground reference. The measurement outcome, however, does not necessarily reproduce the behavior of the device in an actual circuit where a ground reference does not exist. Furthermore, inductor measurements can be affected by the unequal currents on the inner and outer conductors of the coaxial lines internal to the RF probes. Such currents tend to radiate the microwave energy into the surroundings and manifest themselves as unexpected ripple and resonance features in measurement results. In this study, a measurement model is developed including both effects and is used to analyze experimental data obtained from integrated spiral inductors. A novel deembedding technique is then proposed and applied to eliminate the local ground and unequal coaxial current effects.

Mode coupling in coplanar waveguide bends: a simple four-port model

This paper presents a novel four-port model for a 90 ° coplanar waveguide bend based on the decomposition of the waveguide into two coupled slot lines. The effect of the bend discontinuity is that of a non-uniform coupled line system due to the different slot lengths in the structure. The new model consists of uniformly coupled lines and cascaded uncoupled transmission line sections. The parameters for the coupled line system are obtained from the geometry of the bend. The modal transmission coefficients obtained with the model match well with full-wave simulations. The salient feature of the model is the simplified illustration of the frequency-dependent effects of the bend discontinuity. The occurrence of mode-conversion in the two-mode system and its effect on two-port measurements are also described.

Optimized impedance standard substrate designs for dual and differential applications

Optimized dual signal Impedance Standard Substrate (ISS) designs are demonstrated. The optimal designs had loop-under grounds, were selected for minimum deviation from lumped element behavior and used mode dampening structures. A comparison of existing design approaches is given and the quality of the designs is illustrated to 50 GHz.

A high isolation dual signal probe technology

In this paper, we describe a new dual signal probe, and vector network analyzer (VNA) calibration standards providing high isolation between signals. Previously existing probes and standards may exhibit high coupling, making them unsuitable for use with conventional VNAs. The new design significantly reduces the signal-to-signal coupling of the probes and standards, enabling improved calibration and measurement to beyond 40 GHz.