William B. Kuhn

Analysis of current crowding effects in multiturn spiral inductors

The effective trace resistance of a multiturn spiral inductor operating at high frequencies is known to increase dramatically above its dc value, due to proximity effect or current crowding. This phenomenon, which dominates resistance increases due to skin effect, is difficult to analyze precisely and has generally required electromagnetic simulation for quantitative assessment. Current crowding is studied in this paper through approximate analytical modeling, and first-order expressions are derived for predicting resistance as a function of frequency. The results are validated through comparisons with electromagnetic simulations and compared with measured data taken from a spiral inductor implemented in a silicon-on-sapphire process.

A 200 MHz CMOS Q-enhanced LC bandpass filter

This paper presents design techniques and performance bounds for implementing Q-enhanced, LC bandpass filters in silicon IC technologies. These filters offer significant advantages over switched capacitor and Gm-C based designs, including higher frequency of operation and lower power consumption for a given dynamic range. A prototype 200 MHz, fourth-order filter implemented in a 2 /spl mu/m n-well CMOS process is described, and measured performance is compared with theoretical predictions. The prototype filter operates at a selectivity Q of 100 and draws less than 8 mA when operating from 3 to 5 V supplies, making it potentially suitable for use as a first IF filter in modern cellular and PCS receivers.

Q-enhanced LC bandpass filters for integrated wireless applications

Q-enhanced LC filter technology offers an alternative to the use of direct conversion techniques for implementing fully integrated receivers. Design and performance issues for QE LC filters are discussed and a fully integrated 850 MHz, two-pole, bandpass filter with an 18 MHz 3 dB bandwidth is reported. The prototype design is implemented in a standard 0.8 /spl mu/m CMOS process and achieves a rejection of over 50 dB at 100 MHz offset, an in-band dynamic range of 75 (90) dB when used in a system with a 1 MHz (30 kHz) final IF bandwidth, and a third-order intercept point that exceeds +25 dBm at an 80 MHz offset from the passband center,.

A 2.5-GHz low-power, high dynamic range, self-tuned Q-enhanced LC filter in SOI

Q-enhanced LC filter technology offers a promising approach to remove the off-chip preselect filter still required in current transceivers. However, reported designs fail to meet stringent system specifications such as dynamic range and noise figure for existing wireless standards. The complexity and inaccuracy of frequency and Q tuning have also prevented acceptance in industry applications. This paper presents a low-power and high-performance design targeted at Bluetooth in a silicon-on-isolator (SOI) CMOS process. Drawing 5 mA from a 3-V supply, it achieves 23-dB voltage gain (14-dB power gain), approximately 6-dB noise figure, and a 153-dB/spl middot/Hz 1-dB compression point dynamic range, when operating with a 70-MHz bandwidth at 2.5 GHz. A simplified approach to frequency and Q tuning is also demonstrated, making Q-enhanced LC filtering feasible in industry application for the first time.

Bandpass /spl Sigma//spl Delta/ modulator employing undersampling of RF signals for wireless communication

The rapid development of digital wireless systems has led to a need for high-resolution and high-speed bandpass analog-to-digital converters. Continuous-time bandpass /spl Sigma//spl Delta/ modulators are very suitable for such high frequency applications. In this paper, analysis and simulation of a continuous-time bandpass /spl Sigma//spl Delta/ modulator for use in modern cellular/PCS receivers is given. The design employs undersampling relative to a radio receivers radio frequency (RF) or intermediate frequency (IF) center frequency, while oversampling the signal bandwidth. This technique enables clocking at a frequency much lower than the RF/IF frequency, allowing use of standard CMOS technology and reducing the complexity and power consumption of subsequent digital signal processing stages. The analysis shows that it is possible to achieve a loop transfer function that matches a standard discrete-time bandpass /spl Sigma//spl Delta/ modulator while operating at sample rates significantly lower than conventional bandpass architectures.

Printed microinductors on flexible substrates for power applications

A low-profile microinductor was fabricated on a copper-clad polyimide substrate where the current carrying coils were patterned from the existing metallization layer and the magnetic core was printed using a magnetic ceramic-polymer composite material. Highly loaded ferrite-polymer composite materials were formulated, yielding adherent films with 4/spl pi/M/sub s//spl ap/3900 G at +5000 Oe applied DC field. These composite magnetic films combine many of the superior properties of high temperature ceramic magnetic materials with the inherent processibility of polymer thick films. Processing temperatures for the printed films were between 100/spl deg/C and 130/spl deg/C, facilitating integration with a wide range of substrates and components. The quality factor of the microinductor was found to peak at Q=18.5 near 10 MHz, within the optimal frequency range for power applications. A flat, nearly frequency independent inductance of 1.33 /spl mu/H was measured throughout this frequency range for a 5 mm/spl times/5 mm component, with a DC resistance of 2.6 /spl Omega/ and a resonant frequency of 124 MHz. The combination of printed ceramic composites with organic/polymer substrates enables new methods for embedding passive components and ultimately the integration of high Q inductors with standard integrated circuits for low profile power electronics.

Dynamic range of high-Q OTA-C and enhanced-Q LC RF bandpass filters

Dynamic range limitations of high-Q operational transconductance amplifier capacitor (OTA-C) active bandpass filters are reviewed, and expressions are derived relating the dynamic range to the power consumed by the active circuitry. Similar expressions are then derived for the case of inductor/capacitor (LC) filters whose Q have been increased through active, negative resistance circuitry. It is shown that for a fixed power consumption and bandwidth, the enhanced-Q LC filter realizes a factor of Q/sub 0//sup 2/ improvement in dynamic range over the OTA-C filter, where Q/sub 0/ is the quality factor of the passive LC circuit. The reasons for the improvement are discussed and the importance of the improvement is illustrated for active RF bandpass filters employed in radio receiver applications.

Modeling spiral inductors in SOS processes

Existing models for simulating spiral inductors fabricated in silicon processes are outgrowths of the PI structure originally employed by Nguyen and Meyer (1990). This structure and its subsequent elaborations work well for inductors in which the dominant loss mechanism is the underlying substrate. For newer processes with very high resistivity or insulating substrates such as Silicon-on-sapphire however, the model breaks down since inductor quality factor Q is then determined predominantly by series trace resistance. Models suitable for use in such processes are proposed and compared with measured data. The new models contain only four to six elements and, unlike the classic PI model, provide a broadband match to measured impedance behavior in both differentially driven and single-ended circuit applications.

Spiral inductor substrate loss modeling in silicon RF ICs

Spiral inductors constructed in silicon IC technologies possess limited quality factors due to series resistive losses, and losses within the semiconducting substrate. A new model for the less understood substrate losses illustrates how these losses can be minimized, providing quality factor increases of up to 230 percent over un-optimized designs.

Synthesis of polymer-derived ceramic Si(B)CN-carbon nanotube composite by microwave-induced interfacial polarization.

We demonstrate synthesis of a polymer-derived ceramic (PDC)-multiwall carbon nanotube (MWCNT) composite using microwave irradiation at 2.45 GHz. The process takes about 10 min of microwave irradiation for the polymer-to-ceramic conversion. The successful conversion of polymer coated carbon nanotubes to ceramic composite is chemically ascertained by Fourier transform-infrared and X-ray photoelectron spectroscopy and physically by thermogravimetric analysis and transmission electron microscopy characterization. Frequency dependent dielectric measurements in the S-Band (300 MHz to 3 GHz) were studied to quantify the extent of microwave-CNT interaction and the degree of selective heating available at the MWCNT-polymer interface. Experimentally obtained return loss of the incident microwaves in the specimen explains the reason for heat generation. The temperature-dependent permittivity of polar molecules further strengthens the argument of internal heat generation.