Communications: directive radio wave systems and devices (e.g. – Radar transponder system – Radar transponder only
Reexamination Certificate
2001-05-23
2004-11-30
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar transponder system
Radar transponder only
C342S042000, C342S043000, C342S050000, C342S060000, C342S175000, C375S147000, C375S150000, C375S151000, C375S152000, C375S153000
Reexamination Certificate
active
06825794
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to short range communications using surface acoustic wave (SAW) expanders and compressors.
2. Description of the Prior Art
SAW technology is well known for its excellent radio frequency (RF) performance, low cost and small size. SAW is a passive thin film technology that does not require any bias current in order to function. SAW expanders and compressors have been used in RADAR applications for many years.
The basic “building block” of SAW expanders and compressors is the interdigital transducer (IDT) such as shown in FIG.
1
. An IDT
10
is a series of thin metal strips or “fingers”
12
fabricated on a suitable piezoelectric substrate
14
. One set of fingers is connected to an input/output terminal
16
, while the opposite set of fingers is connected to another terminal
18
. In single-ended IDTs, terminal
18
is grounded. For differential input signals however, terminal
18
is a pulse input/output terminal. Spacing “W” between IDT segments is adjusted to conform to the desired chip period of the coded sequence. When excited by a narrow pulse at terminal
16
, the IDT generates a coded output SAW which propagates in both directions perpendicular to the fingers
12
. If a similarly coded SAW impinges on the fingers
12
, then an autocorrelation function is performed and a peak, with associated side lobes, is generated at terminal
16
. These abilities of SAW expanders and compressors are well known in the prior art, having been demonstrated for example in Edmonson, Campbell and Yuen, “Study of SAW Pulse Compression using 5×5 Barker Codes with Quadraphase IDT Geometries”, 1988
Ultrasonics Symposium Proceedings
, Vol. 1, 2-5 October 1988, pp. 219-222.
Thus the structure shown in
FIG. 1
can operate as both a SAW expander, generating a SAW output from a single pulse input, and a SAW compressor, generating a single pulse or peak output from a SAW input. Terminal
16
, as well as terminal
18
in differential IDTs, is both a pulse input terminal and a pulse output terminal. Conversion of an output SAW into an electrical signal for further processing in conventional communications circuits and subsequent transmission through an antenna is accomplished by adding a transmit IDT
24
, aligned with the IDT
22
, as shown in FIG.
2
. Both IDTs can be fabricated on the same substrate
14
. A SAW output from IDT
22
is converted into an electrical signal by TX IDT
24
. A SAW receiver would have the same structure as in
FIG. 2. A
signal input to a receive IDT from receiver processing circuitry would be converted to a SAW which is input to IDT
22
. Like the IDT
22
, the TX IDT
24
may be a differential IDT, wherein the grounded lower terminal would be a pulse output terminal.
The geometry of adjacent IDT fingers
12
is shown in
FIG. 3
, where Tf is the width of a metallized finger
12
and Ts is the width of the space between the fingers
12
. In typical designs both Tf and Ts are equal to a quarter of a wavelength, &lgr;/4. Since wavelength is inversely proportional to frequency of operation, higher frequency IDTs require thinner fingers
12
located in close proximity to each other, which complicates fabrication and reduces fabrication yields. For example, for a typical SAW system operating in the Industrial, Scientific and Medical (ISM) band at 2.4 GHz the &lgr;/4 dimension could be in the order of 0.425 microns, depending upon the substrate chosen.
Previous communications system designs sought to overcome these manufacturing difficulties by using lower frequency SAW expanders and compressors having larger and further spaced fingers in conjunction with mixers and local oscillators, as shown in FIG.
4
. In the typical prior art communication system
30
, the lower frequency 266 MHz signal generated by transmit IDT
20
is up-converted in mixer
34
, which receives a 734 MHz signal from local oscillator
36
. The output from mixer
34
is filtered in high pass filter
38
to produce a 1 GHz signal which is transmitted through antenna
40
. On the receive side, the process is reversed in antenna
42
, mixer
44
, low pass filter
46
and receive compressor IDT
20
′. As discussed above, transmit IDT
20
and receive IDT
20
′ have similar structure. Undesirably, the mixers
34
and
44
, oscillator
36
and filters
38
and
46
from the communications system
30
, result in additional cost, power consumption, occupation in space and a much complex system than is desired for low-cost, low power, short range communication systems. Therefore, there remains a need in the art to reduce the number of components in such a communication system.
High-frequency communication techniques involving more conventional non-SAW based circuits and systems also exist. Bluetooth™ wireless technology is one such prior art example. Bluetooth is a de facto standard, as well as a specification for small-form factor, low-cost, short range radio links between mobile PCs, mobile phones and other portable wireless devices. The current Bluetooth short range communications specification operates in the 2.4 GHz (ISM) band; however, in reality the technology for mobile communication devices involves undesirable high cost, substantial power consumption and relatively complex hardware.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome some of the drawbacks of the prior art.
It is also an object of the present invention to provide a low cost SAW-based communication method and system. As an illustrative example of the cost reduction, SAW devices utilized by the present invention for filtering at near-ISM band frequencies may cost approximately $1.00 each. In contrast, a comparable semiconductor Bluetooth solution may cost greater than $10.00.
It is a further object of the invention to provide SAW-based transmit and receive units which are easily manufactured. The manufacturing required for the present invention allows for SAW fabrication that utilizes simple, single layer photolithographic techniques.
Another object of the invention is to provide a low power SAW solution for short range communications. The SAW uses passive thin film technology and requires only a pulse to excite and produce an RF waveform. Likewise it can perform an autocorrelation function passively. This compares to prior SAW techniques which require frequency conversion circuitry such as mixers, filters and oscillators, and the complex Bluetooth techniques that require separate receive, transmit and processing circuitry. In mobile communication environments, power consumption and size are of primary importance.
A still further object of the invention is to provide a SAW-based communication arrangement which occupies minimal space. A complete SAW package in accordance with the invention is in the order of 3 mm×3 mm.
The inventive SAW system reduces manufacturing complexity and cost and increases production yields by exploiting second harmonic components produced by expander/compressor IDTs. This allows the IDTs to be fabricated with larger finger widths than would be required according to known IDT methods and devices.
In the invention, a wireless communication system comprises an expander/compressor interdigital transducer (IDT) which produces a surface acoustic wave (SAW) output comprising frequency components at a fundamental frequency and a plurality of harmonic frequencies when excited with an electric input signal and produces an electric output signal when excited by a SAW input at the fundamental frequency or one or more of the plurality of harmonic frequencies, a transmit IDT positioned adjacent to the expander/compressor IDT and switchably connected to an antenna, and a receive IDT positioned adjacent to the expander/compressor IDT and switchably connected to the antenna, wherein the transmit IDT and the receive IDT are configured to operate at one of the harmonic frequencies.
In accordance with another aspect of the invention, a communication system comprises an expander IDT configured to produce a S
Campbell Colin K.
Edmonson Peter J.
Gregory Bernarr E.
Jones Day
Meyer Charles B.
Pathiyal Krishna K.
Research In Motion Limited
LandOfFree
Wireless communication system using surface acoustic wave... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wireless communication system using surface acoustic wave..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wireless communication system using surface acoustic wave... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3320328