Frederick Y. Cho

Temperature Stable SAW Devices Using Doubly Rotated Cuts of Quartz

Results of a numerical study of the temperature characteristics of surface acoustic waves (SAW) on doubly rotated cuts of alpha quartz are compared with experimental measurements. The comparison indicates that the first order Temperature Coefficient of Frequency TCF(1) was accurately predicted by Sinha and Tierstens perterbation approach. The experimental data and the calculated values using the Finite Difference approach for the second and third order TCFs were also in good agreement. Families of cuts on alpha quartz with SAW temperature stability superior to that found on ST-cut quartz are identified. Second order TCFs of -0.93 x lo8 were calculated with zero TCFl. Coupling coefficients, power flow angles, phase-temperature plots and other parameters are given for selected cuts.

Variable Delay Line

A variable delay line includes a shift register responsive to coarse adjustment control and a fine adjustment control. The variable delay line can be used in a delay lock loop within an integrated circuit. The variable delay line receives coarse and fine adjustment controls from phase comparators within a phase detector. The coarse and fine adjustment controls cause a shift register associated with the delay element to shift varying amounts, thereby causing a varying amount of delay to be added or removed from the variable delay line. The shift register can be grouped into blocks, and the shift register can shift a block at a time in response to the coarse controls. The variable delay line can also include coarse delay cells associated with one shift register and fine delay cells associated with another shift register. One shift register adds or removes coarse delay cells in response to the coarse controls, the other shift register adds or removes fine delay cells in response to the fine controls.

Manufacturing Technology for a SAW Hybrid Tapped Delay Line

A manufacturing capability to produce 5,000 SAW hybrid tapped delay line modules per month is being established. Production processesand material components to obtain optimum manufacturing cost and performance reliability have been selected. The hybrid SAW delay line has 10 electrically-selectable delay times ranging from 460 ns to 6,050 ns over a 100 MHz bandwidth. The lithium niobate delay line crystal is hybrid integrated with a switching network on an alumina substrate using thick film and chip and wire techniques. Batch processing to increase production yield and automatic testing to reduce the production labor cost have been established. Devices have undergone extensive performance, environmental, and life testing. Over 1,000 units have been built and tested to date using the improved manufacturing techniques.

Single-phase, unidirectional transducer design for charge transport devices

Expressions for calculating the per-stripe reflectivity of aluminum stripe and grooved reflectors as a function of stripe width and thickness are given. These results are used to predict the performance of unidirectional SAW (surface acoustic wave) transducers on gallium arsenide substrates for ACT and HACT (heterojunction acoustic charge transport) applications. The objective is to build the transducers using the same materials used for the NDS (nondestructive sense) Schottky barriers in (H)ACT devices, minimizing the number of photolithographic steps required and maintaining SAW equiphase front alignment to the NDS structures across the devices channel width. In turn, the optimization of the materials systems for large reflectivity in the SAW transducer structure dictates that the NDS structures be designed to minimize net acoustic reflections by these taps in order to maintain the low acoustic standing wave ratio required for high charge transfer efficiency.<<ETX>>

SAW-Laser Communication Link

This paper presents a method for modulating a laser diode using a SAW biphase code. The modulated laser signal is detected and correlated by a second SAW correlator. The laser communication link improves the processing gain in excess of 20 dB. The technology provides potential for a long propagation range, secured, low probability of interception, laser communication link.