Robert W. Brocato

UWB communication using SAW correlators

A simple approach to ultra-wideband (UWB) communication has been demonstrated using surface acoustic wave (SAW) correlators to provide direct RF-to-baseband conversion. The SAW correlators used are bi-phase shift key (BPSK) coded devices that can directly generate or detect an RF signal. This continuous wave (CW) approach to UWB communication is markedly different from the prevailing pulse-based techniques and offers advantages of simplicity, lower component count, and lower cost. The resulting transmitter and receiver architectures eliminate mixers, IF amplifiers, IF filters, and most baseband signal processing. Transmitters and receivers were built operating at 915 MHz, 2.43 GHz, and 5.6 GHz using SAW correlators with 1.25%, 3.3%, 12.5% ,25%, and 50% fractional bandwidths.

Ultra-wideband SAW correlator

A surface acoustic wave (SAW) correlator that satisfies FCC bandwidth requirements for ultra-wideband (UWB) operation has been built and tested. The correlator operates within the 3.1 to 10.6 GHz bandwidth region and uses bi-phase shift keying (BPSK) modulation to achieve a spreading of the main lobe to a 25% bandwidth. This device is capable of spreading or de-spreading a UWB signal directly to or from base-band to microwave frequencies.

IMEMS accelerometer testing-test laboratory development and usage

An economical IMEMS accelerometer test lab was developed by adding acceleration stimulation equipment to an IC test lab. This paper will describe an R&D approach to testing these accelerometers. Descriptions and usage of the equipment are presented. Accelerometer pulse stream data and their analysis are described. A production test facility is being developed from this work.

High frequency SAW correlator module

Surface Acoustic Wave (SAW) correlators were developed which function with central kequencies ranging fiom 300 h4Hz to 2.7 GHz. These devices enable direct translation of data to RF and back without the use of intermediate frequency stages. Several impediments to the manufacture of SAW correlators were overcome. In addition, a programmable SAW correlator built as a flip-chip combination of lithium niobate on silicon was demonstrated.

Combined unsigned and two's complement saturating multipliers

In many digital signal processing and multimedia applications, results that overflow are saturated to the most positive or most negative representable number. This paper presents efficient techniques for performing saturating n-bit integer multiplication on unsigned and twos complement numbers. Unlike conventional techniques for saturating multiplication, which compute a 2n-bit product and then examine the n most significant product bits to determine if overflow has occurred, the techniques presented in this paper compute only the (n + 1) least significant bits of the product. Specialized overflow detection units, which operate in parallel with the multiplier, determine if overflow has occurred and the product should be saturated. These techniques are applied to designs for saturating array multipliers that perform either unsigned or twos complement saturating integer multiplication, based on an input control signal. Compared to array multipliers that use conventional methods for saturation, these multipliers have about half as much area and delay.

Miniature high voltage, high temperature component package development

With the next generation of semiconductor materials in development, significant strides in the Size, Weight, and Power (SWaP) characteristics of power conversion systems are presently underway. In particular, much of the improvements in system-level efficiencies and power densities due to wide-bandgap (WBG) and ultra-wide-bandgap (UWBG) device incorporation are realized through higher voltage, higher frequency, and higher temperature operation. Concomitantly, there is a demand for ever smaller device footprints with high voltage, high power handling ability while maintaining ultra-low inductive/capacitive parasitics for high frequency operation. For our work, we are developing small size vertical gallium nitride (GaN) and aluminum gallium nitride (AlGaN) power diodes and transistors with breakdown and hold-off voltages as high as 15kV. The small size and high power densities of these devices create stringent requirements on both the size (balanced between larger sizing for increased voltage hold-off with smaller sizing for reduced parasitics) and heat dissipation capabilities of the associated packaging. To accommodate these requirements and to be able to characterize these novel device designs, we have developed specialized packages as well as test hardware and capabilities. This work describes the requirements of these new devices, the development of the high voltage, high power packages, and the high-voltage, high-temperature test capabilities needed to characterize and use the completed components. In the course of this work, we have settled on a multi-step methodology for assessing the performance of these new power devices, which we also present.

Real-time RF spectrum analyzer: Components and system development

Many wireless communication links quickly hop between narrow frequency channels. Many such connections can occur simultaneously in the same band and hop in a standard pseudorandom frequency pattern dwelling a predetermined time in each channel. To sense modern communication, a real-time spectrum analyzer is very useful. One large advantage of real time analysis is that it only records data in active channels because it can determine the activity in each time interval. Another advantage is that communication that is not adhering to FCC standards can also be discerned. A van full of RF amplifiers, digitizers, and Fourier analysis equipment has been used for this job in non-real time. We chose to attack this design by providing many identical signal paths, one for each frequency channel. A number of RF components had to be developed to make this circuit power efficient and fit a small footprint. The initial broad band signal from an antenna sees low noise amplification (LNA) and then is divided into many identical RF signal paths using silicon germanium integrated circuits (SiGe RFICs). Each of these RF signals is filtered by one filter in a ladder of frequency adjacent SAW filters. The output of each SAW device is compared with the RF power seen in the previous time interval to see if there is less or more of a signal. Up to this point the system has been low- power analog. Once the RF channel powers are quantified, the system uses a digital signal processor (DSP) to further analyze signal characteristics.

Re-configurable Completely Unpowered Wireless Sensors

A methodology for remotely and wirelessly reading any type of unpowered impedance varying sensor is described. Unpowered wireless sensors, in existence for a number of years, have been limited to low impedance sensors. Techniques for reading high impedance sensors are introduced here. The resulting methodology can be used to measure a wide range of different sensors, including temperature, pressure, light level, mechanical switch, acoustic emission, and acceleration. These sensors report physically measurable data in the same manner as do similar conventional sensors, but they do it remotely and without any local power source. The sensors are measured remotely using a radar-like interrogation device, and the sensors and their related communication electronics draw all of the power needed for communicating from the radar pulse.

Effect of critical dimension variation on SAW correlator energy

The effect of critical dimension (CD) variation and metallization ratio on the efficiency of energy conversion of a surface acoustic wave (SAW) correlator is examined. We find that a 10% variation in the width of finger electrodes predicts only a 1% decrease in the efficiency of energy conversion. Furthermore, our model predicts that a metallization ratio of 0.74 represents an optimum value for energy extraction from the SAW by the interdigitated transducer (IDT).

Microsystem packaging of an RF SAW correlator

An electrically programmable surface acoustic wave (SAW) correlator was recently completed from design through small scale production in support of low power space-based communications for NASA. Three different versions of this RF microsystem were built to satisfy design requirements and overcome packaging and system reliability related issues. Flip-chip packaging and conventional thick film hybrid assembly techniques are compared in the fabrication of this microsystem.