Pulse or digital communications – Receivers – Angle modulation
Reexamination Certificate
1998-03-26
2001-02-27
Tse, Young T. (Department: 2734)
Pulse or digital communications
Receivers
Angle modulation
C375S345000, C375S349000, C329S307000, C455S136000
Reexamination Certificate
active
06195400
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a two-mode demodulating apparatus suitable for use in a radio terminal in, for example, a mobile communication system.
(2) Description of Related Art
Shortage of frequency bands usable as transmission frequencies with an increase of subscribers is showing up in recent radio communication system, which causes troubles in communication such that a telephone line is often interrupted or a telephone communication becomes broken, etc. In order to avoid such troubles in the communication, there have been developed and operated various techniques of improving efficiency of frequency utilization as countermeasures.
A digital communication system having a higher efficiency of frequency utilization using a linear modulation system comes to be used, for instance. However, the number of base stations to which such digital communication system having a higher efficiency of frequency utilization is still insufficient and an area in which the digital communication can be used is limited, as compared with analog communication systems using known linear modulating systems.
There is a demand for a communication terminal which can use both of the above two communication system to make a communication in a digital communication system in an area in which the digital communication system is usable, while making a communication in an analog system in an area in which the digital communication system is not usable but only an analog communication system is usable.
FIG. 12
is a block diagram showing a two-mode demodulating apparatus used as a receiving unit of a communication terminal being able to use two communication systems as above. Namely, a two-mode receiving apparatus
100
shown in
FIG. 12
has a linear wave receiving circuit
110
, a non-linear wave receiving circuit
120
and a digital processing unit
130
.
In the two-mode receiving apparatus
100
shown in
FIG. 12
, the digital processing unit
130
can control the linear wave receiving circuit
110
to receive a linear modulated wave signal, and the non-linear wave receiving circuit
120
to receive a non-linear modulated wave signal of intermediate frequency (IF) signals as received signals.
The linear wave receiving circuit
110
has a variable gain amplifier
111
, multipliers
112
I and
112
Q, a 90° phase shifter
114
, linear wave receiving band-limit filters
115
I and
115
Q, high-speed A/D (Analog/Digital) converters
116
I and
116
Q, a frequency finely tunable temperature-compensated oscillator (VC-TCXO)
117
, and a PLL (Phase Locked Loop) unit
118
.
The non-linear wave receiving circuit
120
has a multiplier
121
, a local oscillator
122
, a non-linear wave receiving filter
123
, a limiter-amplifier
124
, and a quadrature detector
125
, a non-linear receiving filter
126
and an A/D converter
127
.
The digital processing unit
130
has a liner wave receiving process unit
131
, a local oscillated frequency setting unit
132
, a frequency correcting unit
133
, a gain controlling unit
134
, a received electric field strength computing unit
135
, and a non-linear wave receiving process unit
136
.
In the two-mode receiving apparatus
100
with the above structure shown in
FIG. 12
, a linear modulated wave signal as a received signal received by the linear wave receiving circuit
110
is subjected to an automatic gain control in the variable gain amplifier
111
, mixed with a local signal fed from the PLL unit
118
to be detected in orthogoanl detection in a quasi-synchronous system, whereby baseband signals in two systems are outputted.
The above PLL unit
118
performs a PLL control on a signal from the temperature-compensated oscillator
117
, which has been subjected to a frequency control (quasi-synchronous correction) on the basis of the received signal by the digital processing unit
130
, and outputs the signal as a local signal for the orthogonal detection in the multipliers
112
I and
112
Q.
The baseband signals (analog signals) outputted from the multipliers
112
I and
112
Q are band-limited in the respective linear wave receiving band-limit filters
115
I and
115
Q, converted and demodulated into digital signals in the respective high-speed A/D converters
116
I and
116
Q, and outputted to the digital processing unit
130
in the following stage.
A non-linear modulated wave signal as the receive signal received by the non-linear wave receiving circuit
120
is mixed with a local signal from the local oscillator
122
provided separately from the function unit (refer to reference numerals
117
and
118
) local oscillator
118
outputting the above local signal for receiving a linear modulated wave in the multiplier
121
, and converted into an intermediate frequency signal.
The intermediate frequency signal from the multiplier
121
is limited to a band set in advance by the non-linear wave receiving band-limit filter
123
. In other words, the intermediate frequency signal having passed through the non-linear wave receiving band-limit filter
123
is limited to a signal whose band is fixedly set in advance.
The baseband signal having passed through the non-linear receiving band-limit filter
123
is limited and amplified by the limiter-amplifier
124
, then subjected to a quadrature detection in the quadrature detector
125
configured with a multiplier
125
a
and a phase shifter
125
b.
In the non-linear wave receiving band-limit filter
126
and the A/D converter
127
, only a desired modulated signal is selectively taken out from the baseband signal, converted into a digital signal, and outputted to the digital processing unit
130
in the following stage.
However, in the above two-mode receiving apparatus
100
shown in
FIG. 12
, the non-linear wave receiving band-limit filter
123
in, for example, the non-linear wave receiving circuit
120
is of a large size since it is a passive component applied a resonance phenomenon, resulting in a large scale circuit. If the above two-mode receiving apparatus is applied to a mobile terminal in a mobile communication system, for example, it is difficult to meet a strong demand for portability or compactness of the terminal.
The above non-linear wave receiving band-limit filters
123
and
126
are used to fixedly set respective pass-bands in advance. On the other hand, the non-linear modulated wave passes through a different band according to a type of system (analog communication system) such as AMPS, TACS, NAMPS, NTACS or the like so that it is difficult to versatilely use hardware to an applied non-linear modulated wave system.
In other words, in the above non-linear wave receiving band-limit filters
123
and
126
, it is difficult to dynamically change a pass band. Accordingly, it is necessary to change or switch the filter to be used according to a required non-linear modulation system, besides it is difficult to reduce the cost or improve the reliability when the apparatus including the non-linear receiving filters is formed into an LSI (Large-Scale Integrated circuit).
Meanwhile, a two-mode receiving apparatus
100
A shown in
FIG. 13
has, although having structural elements basically similar to those of the above linear receiving circuit
110
shown in
FIG. 12
, non-linear wave receiving band-limit filters
126
I and
126
Q, and A/D converters
127
I and
127
Q on the output's side of the multipliers
112
I and
112
Q as a receiving system for a non-linear modulated wave, besides using the structural elements of the linear wave receiving circuit
110
(refer to reference numerals
111
,
112
I,
112
Q,
114
,
117
and
118
), thereby reducing a scale of the circuit.
In the two-mode receiving apparatus
100
A shown in
FIG. 13
, a digital processing unit
130
A has a linear wave receiving process unit
131
, a local oscillated frequency setting unit
132
, a frequency correcting unit
133
, a gain controlling unit
134
and a non-linear wave receiving process unit
136
, basically similar to those of the above two-mode receiving apparatus
100
s
Fujitsu Limited
Helfgott & Karas, PC.
Tse Young T.
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