Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-03-11
2001-07-24
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S31300R
Reexamination Certificate
active
06265807
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a spread spectrum communication apparatus used in a spread spectrum communication system, a demodulator used in the communication apparatus, a surface acoustic wave element used in the demodulator, and surface acoustic wave parts used in the demodulator.
In recent years, a spread spectrum communication system (SS communication system) having strong noise resistivity and excellent secrecy and concealability has received attention as a communication system for civil use. In the SS communication system, carrier waves obtained by modulating information to be transmitted by a carrier signal are subjected to spread spectrum modulation (SS modulation) by use of a predetermined code series having a high chip rate to obtain a spread spectrum signal (SS signal) which is transmitted as a transmit signal. In this case, the code series may include a pseudo noise code series (PN code series) and a Barker code series. The SS modulation system may include a direct spread system (DS system) and a frequency hopping system (FH system).
In such an SS communication system, the receiver side requires a demodulator for demodulating the SS signal transmitted thereto. For example, in the case where the SS modulation is based on the DS system by use of the PN code series, the receiver side uses the same PN code series as that on the transmitter side for demodulation. At this time demodulators are roughly divided into demodulators using ICS and demodulators using surface acoustic wave elements. A surface acoustic wave element used in a demodulator has become an object of attention since the demodulator can be fabricated at a low cost and with a simple construction by using a photolithography technique for formation of the surface acoustic wave element.
Surface acoustic wave elements can be classified into surface acoustic wave matched filters and surface acoustic wave convolvers from the structural aspect. In the surface acoustic wave convolver, it is possible to select a PN code series which is used for modulation. Therefore, the surface acoustic wave convolver is suitable for use in applications in which secrecy and concealability are especially required. In the surface acoustic wave matched filter, a PN code series used for modulation is fixed but a peripheral circuit can correspondingly be formed with a simple construction, thereby providing the whole system at a low cost. Therefore, the surface acoustic wave matched filter has become an object of attention as a demodulator used in a small-scale SS communication system, for example, a private wireless LAN.
The construction of a conventional demodulator for a DS system using a surface acoustic wave matched filter is shown by
FIG. 11
in block diagram. In the figure, reference numeral
61
denotes a surface acoustic wave matched filter inputted with an SS signal s for outputting a correlation signal m, numeral
62
denotes a surface acoustic wave delay line for delaying the correlation signal m from the surface acoustic wave matched filter
61
by one period, numeral
63
denotes an integrating circuit for integrating the correlation signal m from the surface acoustic wave matched filter
61
and a correlation signal n from the surface acoustic wave delay line
62
subjected to the delay of one period, numeral
64
denotes an amplifier for amplifying the correlation signal m from the surface acoustic wave matched filter
61
, and the symbols L
1
and L
2
denote signal lines.
The operation of the demodulator shown in
FIG. 11
will now be explained briefly. An SS signal s inputted to the surface acoustic wave matched filter
61
is converted by the surface acoustic wave matched filter
61
into a correlation signal m which is in turn divided into two systems including the lines L
1
and L
2
. The correlation signal m on the line L
1
is inputted directly to the integrating circuit
63
. The correlation signal m on the other line L
2
is inputted to the surface acoustic wave delay line
62
through the amplifier
64
so that it is inputted to the integrating circuit
63
as a correlation signal n delayed by one period. The integrating circuit
63
integrates the correlation signal m and the one-period delayed signal n to obtain a demodulated signal.
FIG. 12A
is a pattern diagram showing the surface acoustic wave matched filter in the demodulator shown in FIG.
11
. In
FIG. 12A
, reference numeral
71
denotes a piezoelectric substrate made of quartz crystal, LiNbO
3
or the like, numeral
72
denotes a signal input electrode, numeral
73
denotes an output encoding electrode, and numeral
74
denotes an acoustic material member for absorbing unnecessary surface acoustic waves. Next, an explanation of operation will be made. The signal input electrode
72
has a comb form for converting an electric signal into surface acoustic waves. The output encoding electrode
73
is separated from the electrode
72
by a predetermined interval and converts the surface acoustic waves into an electric signal. The electrodes
72
and
73
are provided on the piezoelectric substrate
71
to form a surface acoustic wave matched filter. In the case where a PN code series of n bits is used, the output encoding electrode
73
has n comb-like electrode pairs corresponding to the n-bit PN code series and the comb-like electrode pairs are formed at intervals corresponding to the chip rate. In this case, the number of pairs of electrodes (or electrode fingers) in a comb-like electrode pair is 1 (one). For the purpose of absorbing unnecessary surface acoustic waves, the acoustic material members
74
are formed outside of the input and output electrodes
72
and
73
, as required. In this case, the signal input electrode
72
and the output encoding electrode
73
may be reversed, that is, the signal input electrode
72
and the output encoding electrode
73
may be used as an output electrode and an input electrode, respectively.
FIG. 12B
is a pattern diagram showing the surface acoustic wave delay line in the demodulator shown in FIG.
11
. In
FIG. 12B
, reference numeral
75
denotes a piezoelectric substrate made of quartz crystal, LiNbO
3
or the like, numeral
76
denotes a signal input electrode, numeral
77
denotes a signal output electrode, and numeral
78
denotes acoustic material members for absorbing unnecessary surface acoustic waves. Next, an explanation of operation will be made. The signal input electride
76
has a comb form for converting an electric signal into surface acoustic waves. The signal output electrode
77
also has a comb form and is separated from the electrode
76
by an interval corresponding to one period T of a signal to be received and demodulated. The electrode
77
converts the surface acoustic waves into an electric signal. The electrodes
76
and
77
are provided on the piezoelectric substrate
75
to form a surface acoustic wave delay line. For the purpose of absorbing unnecessary surface acoustic waves, the acoustic material members
74
are formed outside of the input and output electrodes
76
and
77
, as required.
A demodulator using such a surface acoustic wave matched filter performs demodulation by use of two polarities (for example, 0 phase and &pgr; phase) which the surface acoustic wave matched filter takes. The modulation system corresponds to binary phase shift keying system (BPSK system).
Though the transmission rate of information in a wireless LAN or the like is as high as possible, the transmission rate in an SS communication is restricted by the band width of the SS communication system itself and the PN code series that is used. Namely, it is required that the transmission rate should be lower than a value obtained by dividing the band width by 2n, wherein n is the number of bits in the PN code series. From the aspect of transmission rate, therefore, it is preferable that the number of bits in the PN code series is made small. However, if the number of bits in the PN code series is too small, there is an inconvenience in that the secrecy or concealab
Koga Naoki
Ohtsuka Masatoshi
Tomari Seishi
Dougherty Thomas M.
Frank Robert J.
Matsushita Electric - Industrial Co., Ltd.
Venable
Wood Allen
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