 |
Description  |
|
|
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 112I and 112Q, a 90.degree. phase shifter 114, linear wave
receiving band-limit filters 115I and 115Q, high-speed A/D
(Analog/Digital) converters 116I and 116Q, 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 112I and
112Q.
The baseband signals (analog signals) outputted from the multipliers 112I
and 112Q are band-limited in the respective linear wave receiving
band-limit filters 115I and 115Q, converted and demodulated into digital
signals in the respective high-speed A/D converters 116I and 116Q, 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 125a and a phase shifter 125b. 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 100A 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 126I and 126Q, and A/D converters 127I and
127Q on the output's side of the multipliers 112I and 112Q 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, 112I, 112Q, 114, 117 and 118), thereby reducing a scale of
the circuit.
In the two-mode receiving apparatus 100A shown in FIG. 13, a digital
processing unit 130A 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 shown in FIG. 12.
The two-mode receiving apparatus 100A shown in FIG. 13 receives and
demodulates a linear modulated wave in the same way as the above two-mode
receiving apparatus 100 shown in FIG. 12 when receiving the linear
modulated wave. When receiving a non-linear modulated wave, the two-mode
receiving apparatus 100A shown in FIG. 13 performs an automatic gain
control, then converts the non-linear modulated wave into baseband signals
in two systems, as well as the above linear modulated wave.
However, in the above two-mode demodulating apparatus 100A shown in FIG.
13, the non-linear wave receiving band-limit filters 126I and 126Q are not
variable. In addition, it is impossible to completely eliminate
steady-state frequency deviation in the quasi-synchronous detection system
so that it is difficult to perform a demodulating process corresponding to
each of various non-linear modulated waves (particularly, NAMPS, NTACS,
etc.).
Namely, although the above two-mode receiving apparatus 100A shown in FIG.
13 converts not only a linear wave modulated signal but also a non-linear
wave modulated signal into baseband signals in two systems in the
quasi-synchronous detection system, it is difficult to demodulate the
signal with a high accuracy since frequency deviation in the non-linear
modulated wave in a system such as NTACS, NAMPS or the like is
particularly small.
In this case, an AFC (automatic frequency control) operation, which is not
required originally in the non-linear receiving circuit, is required in
order to eliminate the above steady-state frequency deviation, besides the
A/D converters 116I, 116Q, 126I and 126Q are required to be provided
separately for the linear modulated wave and the non-linear modulated
wave, which causes an increase in power consumption.
SUMMARY OF THE INVENTION
In the light of the above problems, an object of the present invention is
to provide a two-mode modulating apparatus which can receive and
demodulate a linear-modulated wave and a non-linear modulated wave while
restricting an increase of the circuit scale and the power consumption,
and generalizing a hardware structure for an applied non-linear modulating
system.
The present invention therefore provides a two-mode demodulating apparatus
having a linear reception demodulating circuit and a non-linear reception
demodulating circuit, in which the linear reception demodulating circuit
and the non-linear reception demodulating circuit can be selectively
operated by selecting a mode, the two-mode demodulating apparatus
comprising the linear reception demodulating circuit comprising first
frequency converting units for frequency-converting a received signal into
a low-frequency signal using a first local signal having a first
oscillated frequency from a variable oscillated-frequency local
oscillator, linear reception demodulating process units for performing
linear reception demodulating processes on outputs of the first
frequency-converting units, the non-linear reception demodulating circuit
comprising a second frequency converting unit for frequency-converting the
received signal into a low-frequency signal using a second local signal
from the local oscillator having a second oscillated frequency different
from the first oscillated frequency of the first local signal, a
variable-band filtering unit for allowing a signal in a desired band
contained in an output of the second frequency converting unit to pass
therethrough, and a non-linear reception demodulating process unit for
performing a non-linear reception demodulating process on an output of the
filtering unit.
When the non-linear reception demodulating circuit is selected, the second
frequency converting unit frequency-converts an intermediate frequency
signal as the received signal into a signal in the vicinity of the
baseband by changing an oscillated frequency of the local oscillator.
The filtering unit may be configured as an active variable-band filtering
unit. In which case, a switched capacitor filter may be used as the
variable-band filtering unit.
The non-linear reception demodulating process unit may have a delay
detecting circuit for performing a delay detecting process on an output
from the filtering unit, and a low-pass filter/analog-to-digital
converting process unit for performing a low-pass filtering process and an
analog-to-digital converting process on an output from the delay detecting
circuit.
The non-linear reception demodulating unit may alternatively have a
frequency measuring circuit for performing a frequency measuring process
on an output from the filtering unit to output a digital demodulated
signal.
The non-linear reception demodulating process unit may still alternatively
have an analog-to-digital converting circuit for receiving an output from
the filtering unit to perform a down sampling operation. In which case,
the analog-to-digital converting circuit may have sample-and-hold circuits
in two systems for extracting two samples at predetermined time intervals
to detect a direction of phase rotation.
The two-mode demodulating apparatus may further have a gain controlling
amplifier for controlling a gain of the received signal before the
received signal is inputted to the linear reception demdoualting circuit
and the non-linear reception demodulating circuit, wherein the non-linear
reception demodulating process unit has an envelope detecting circuit for
performing an envelope detecting process on an output from the filtering
unit and a comparing circuit for comparing an output from the envelope
detecting circuit with a predetermined reference value to output a signal
for controlling the gain controlling amplifier.
According to this invention, there are provided the second frequency
converting unit, the variable-band filtering unit and the non-linear
receiving demodulating process unit to the two-mode demodulating
apparatus. It is thereby possible to cope with various non-linear
modulation systems along with a linear modulation system, while
generalizing a hardware structure for an applied non-linear modulation
system, and accomplishing a common use of the circuit with decreased-scale
hardware.
According to this invention, by providing the frequency measuring circuit
to the two-mode demodulating apparatus, it is possible to directly
demodulate and convert the received signal as an input signal into a
digital signal so that an A/D converting process by an A/D converter is
unnecessary when the two-mode demodulating apparatus receives a nonlinear
modulated wave. Consequently, not only the circuit scale can be decreased
but also the power consumption can be remarkably decreased.
According to this invention, by providing the analog-to-digital converting
circuit for performing a down sampling operation to the two-mode
demodulating apparatus, the received signal as an input signal can be
directly demodulated and converted into a digital signal. Therefore, a
complicated digital processing is unnecessary, thus the control can be
simplified. In addition, it is possible to largely decrease a scale of a
peripheral circuit, whereby the package is decreased and the power
consumption is also largely decreased.
According to this invention, by providing the envelope detecting circuit
and the comparing circuit along with the gain controlling amplifier to the
two-mode demodulating apparatus, it is possible to measure a received
electric field strength with an accuracy as high as a linear receiving
system by a simple system so as to control the received electric field
strength of a received signal even when a non-linear modulated wave is
received.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a two-mode demodulating apparatus
according to a first embodiment of this invention;
FIG. 2 is a functional block diagram showing a mobile station in a mobile
communication system to which the two-mode demodulating apparatus
according to the first embodiment is applied;
FIGS. 3 and 4 are diagrams for illustrating filter characteristics of a
band-limit filter according to the first embodiment;
FIG. 5 is a flowchart for illustrating an operation of the mobile station
in the mobile communication system to which the two-mode demodulating
apparatus according to the first embodiment is applied;
FIG. 6 is a block diagram showing a two-mode demodulating apparatus
according to a second embodiment of this invention;
FIG. 7 is a functional block diagram showing a frequency measuring circuit
according to the second embodiment;
FIG. 8 is a diagram for illustrating a manner of measuring a center
frequency from measured values of the frequency measuring circuit
according to the second embodiment;
FIG. 9 is a block diagram showing a two-mode demodulating apparatus
according to a third embodiment of this invention;
FIG. 10 is a functional block diagram showing a down sampling-A/D converter
according to the third embodiment;
FIG. 11 is a diagram for illustrating a down sampling operation of the down
sampling-A/D converter according to the third embodiment; and
FIGS. 12 and 13 are block diagrams showing known two-mode demodulating
apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, description will be made of embodiments of the present
invention referring to the drawings.
(a) Description of a First Embodiment
FIG. 1 is a block diagram showing a two-mode demodulating apparatus
according to a first embodiment of this invention. A two-mode demodulating
apparatus 7-1 shown in FIG. 1 is applicable to a linear/non-linear
receiving process unit 3 and a digital processing unit 4 as a received
signal processing system of a mobile station 1 in a mobile communication
system as shown in FIG. 2, for example.
The mobile station 1 shown in FIG. 2 has an RF processing unit 2 and the
linear/non-linear receiving process unit 3 as a receiving system, the
digital processing unit 4, and a transmitting process unit 5, thereby
exchanging a linear modulated wave in a digital communication system or a
non-linear modulated wave in an analog communication system with a base
station 6.
The RF processing unit 2 performs frequency conversion on a received signal
(RF signal) in a high frequency, and outputs an intermediate frequency
signal (IF signal) as the received signal. The linear/non-linear reception
processing unit 3 demodulates a linear modulated wave signal or a
non-linear modulated wave signal as the intermediate frequency signal from
the RF processing unit 2, and outputs a digital signal to the digital
processing unit 4.
The digital processing unit 4 performs a power source control on the mobile
station 1, a receiving process such as regeneration or the like on the
received signal demodulated in the linear/non-linear receiving process
unit 3, and a transmitting process on a signal to a base station 6 and a
protocol control. With respect to the linear/non-linear receiving process
unit 3, the digital processing unit 4 has a linear receiving process unit
41, a linear receiving circuit power controlling unit 42, a local
oscillated frequency setting unit 43, a frequency correcting unit 44, a
non-linear receiving circuit power controlling unit 45, a non-linear
receiving process unit 46, a level detecting unit 47, a band variably
controlling unit 48, and a gain controlling unit 49.
The transmitting process unit 5 is inputted transmit data from the digital
processing unit 4 to perform a modulating process in a desired system, and
transmits the data to the base station 6.
The linear/non-linear receiving process unit 3 has, with respect to a
function of the digital processing unit 4 in the following stage, a
variable gain amplifier 111, a linear reception demodulating circuit 10, a
non-linear reception demodulating circuit 20-1, a PLL unit 30 and a
frequency finely tunable temperature-compensated oscillator (VC-TCXO) 50,
as shown in detail in FIG. 1 mentioned above.
The variable gain amplifier 111 performs a gain control on the received
signal having been converted into the intermediate frequency signal in the
RF processing unit 2 before the received signal is inputted to the linear
reception demodulating circuit 10 and the non-linear reception
demodulating circuit 20-1, which functions as a gain-controller amplifier.
As to states of operations of the above linear reception demodulating
circuit 10 and the non-linear reception demodulating circuit 20-1, the
linear reception demodulating circuit 10 and the non-linear reception
demodulating circuit 20-1 may be selectively operated by setting and
controlling a clock frequency as a local signal used when the received
signal is converted into the baseband signals according to a linear
modulated wave or a non-linear modulated wave to be received.
The linear reception demodulating circuit 10 shown in FIG. 1 has, in
detail, multipliers 112I and 112Q, a 90.degree. phase shifter 114, linear
wave receiving band-limit filters 115I and 115Q, high-speed A/D converters
116I and 116Q similar to those shown in FIG. 12 or 13 described
hereinbefore.
After the variable gain amplifier 111 amplifies the received signal under
an automatic gain control, the linear reception demodulating circuit 10
mixes this linear modulated signal with a local signal generated by the
temperature-compensated oscillator 50 and the PLL unit 30 in cooperation
in the multipliers 121I and 121Q, performs orthogonal detection on the
mixed signal in the quasi-synchronous system, thereby outputting baseband
signals in two systems.
The baseband signals (analog signals) outputted from the multipliers 112I
and 112Q are band-limited in the linear wave receiving band-limit filters
115I and 115Q, respectively, converted and demodulated into digital
signals in the respective high-speed A/D converters 116I and 116Q, and
outputted to the linear wave receiving process unit 41 in the digital
processing unit 4 in the following stage.
Therefore, the multipliers 112I and 112Q and the 90.degree. phase shifter
114 mentioned above function as a first frequency converting unit for
frequency-converting the received signal into a low frequency signal using
a first local signal having a first oscillated frequency from the PLL unit
30 having a function as a variable oscillated frequency local oscillator,
whereas the linear wave receiving band-limit filters 115I and 115Q and the
high-speed A/D converters 116I and 116Q function as a linear reception
demodulating process unit for performing a linear reception demodulating
process on outputs of the multipliers 112I and 112Q.
The above PLL unit 30 has functions as frequency dividers 31 and 32, a
phase comparator 33, a loop filter 34 and an oscillator 35 to generate a
signal obtained by performing a PLL control on a clock signal (having been
subjected to a necessary frequency correction on the basis of the received
signal in the frequency correcting unit 44) from the
temperature-compensated oscillator 50 on the basis of frequency
information of the local oscillator set by the local oscillated frequency
setting unit 43.
The frequency divider 31 demultiplies a frequency of the clock signal from
the temperature-compensated oscillator 50, whereas the frequency divider
32 is fed back and inputted a signal as the local signal used when the
above linear modulated wave or the non-linear modulated wave is converted
into the baseband signals to perform a dividing process corresponding to
the above frequency divider 32.
The phase comparator 33 compares phases of the signals from the frequency
dividers 31 and 32. The oscillator 35 is inputted a result of the phase
comparison from the phase comparator 33 via the loop filter 34, and
outputs a clock signal whose phase is controlled to be constant on the
basis of the result of the phase comparison as the local signal.
The PLL unit 30 generates a local signal for orthogonal detection to be
performed on a linear modulated wave signal in the linear reception
demodulating circuit 10 when a linear modulated wave is received, while
generating a local signal for converting a non-linear modulated wave
signal into a signal, described later, containing not only a baseband but
also a band in the vicinity of the baseband when a non-linear modulated
wave is received.
Namely, the signal from the PLL unit 30 is also used as the local signal
when the non-linear modulated wave signal is converted into baseband
signals, thereby accomplishing a common clock generating source upon
signal detection in the linear receiving circuit 10 and the non-linear
receiving circuit 20-1.
The non-linear receiving circuit 20-1 has, in detail, a multiplier 21, a
band-pass filter 22, a limiter amplifier 23, a delay detecting circuit 24,
a non-linear receiving low-pass filter-A/D converter 25, an envelope
detecting circuit 26 and a comparator 27. The non-linear receiving circuit
20-1 can demodulate a received signal in an arbitrary nonlinear modulating
system independent of various systems (AMPS, TACS, NAMPS, NTACS, etc.),
and output the demodulated received signal as a digital signal to the
digital processing unit 4.
The multiplier 21 converts the received signal amplified by the variable
gain amplifier 111 (under the automatic gain control by the gain
controlling unit 49) into a signal (having a low-frequency offset)
containing all bands used upon demodulation in the above various systems
(AMPS, TACS, NAMPS, NTACS, etc.) on the basis of the local signal from the
above PLL unit 30.
In the PLL unit 30, when the non-linear reception demodulating circuit 20-1
is selected as a receive mode, an oscillated frequency of the local signal
genenerated by the PLL unit 30 is changed to an oscillated frequency
different from one used upon linear reception, by switching a setting in
the PLL unit 30 by the local oscillated frequency setting unit 43.
Whereby, the multiplier 21 mixes the non-linear modulated wave signal from
the variable gain amplifier 111 with the local signal from the PLL unit 30
whose oscillated frequency is set by the local oscillated frequency
setting unit 43 to convert the received signal into a signal containing a
band in the vicinity of the baseband.
Therefore, the above multiplier 21 functions as a second frequency
converting unit for frequency-converting the received signal into a low
frequency signal using a second local signal from the PLL unit 30 having a
second oscillated frequency different from the first oscillated frequency
possessed by a first local signal for receiving the linear modulated wave.
The function of the above multiplier 21 may be provided to either the
multiplier 112I or the multiplier 112Q of the above-mentioned linear
receiving circuit 10 so as to be used in common.
The band-pass filter 22 allows only a signal in a band (baseband signal)
corresponding to a system used when the received signal is received among
the above various systems in the signal containing a band in the vicinity
of the baseband converted by the above multiplier 21 to pass therethrough.
In other words, the band-limit filter 22 functions as a variable band
filtering unit for allowing a signal in a desired band contained in an
output of the multiplier 21 so as to provide a band limit adapting a
non-linear modulating system selected as a system to be received on the
received signal from the multiplier 21.
The above band-limit filter 22 may be configured as an active variable band
filtering unit. As this active variable band filtering unit, there may be
used a switched capacitor filter (SCF).
Namely, the band variably controlling unit 48 in the digital processing
unit 4 can variably control a pass-band of the SCF, thereby actively set a
pass-band according to a system to be adapted among various systems of
non-linear modulated waves as above.
If the baseband bandwidth is of a pass-band width 30 kHZ whose center
frequency is 30 kHz, the band-limit filter 22 can be configured by
connecting in series a pair of switched capacitor filters 22A and 22B
having characteristics as shown in FIG. 3, for example.
In which case, the SCF 22A functions as a low-pass filter (LPF) having a
characteristic to allow only lower frequency components than a frequency
of about 45 kHz to pass therethrough, whereas the SCF 22B functions as a
high-pass filter (HPF) having a characteristic to allow only higher
frequency components than a frequency of about 15 kHZ to pass
therethrough.
If the baseband bandwidth is of a pass-band width 25 kHz whose center
frequency is 30 kHz, the band-limit filter 22 can be configured by
connecting in series a pair of switched capacitor filters (SCF; Switched
Capacitor Filter) 22C and 22D having characteristic as shown in FIG. 4,
for example.
In which case, the SCF 22C functions as a low-pass filter (LPF) having a
characteristic to allow lower frequency components than a frequency of
about 37.5 kHz to pass therethrough, whereas the SCF 22D functions as a
high-pass filter (HPF) having a characteristic to allow higher frequency
components than a frequency of about 12.5 kHz to pass therethrough.
The limiter amplifier 23 limits and amplifies the received signal whose
band has been limited by the above band-limit filter 22. The delay
detecting circuit 24 performs a delay detecting process on the received
signal having been limited and amplified by the limiter amplifier 23 to
demodulate the received signal.
The non-linear receiving low-pass filter-A/D converter 25 performs a
low-pass filtering process and an analog-to-digital converting process on
the demodulated signal (analog signal) outputted from the delay detecting
circuit 24, thereby converting the demodulated signal into a digital
signal while eliminating noise components in the demodulated signal.
The limiter amplifier 23, the delay detecting circuit 24 and the non-linear
receiving low-pass filter-A/D converter 25 cooperate to function as a
non-linear reception demodulating process unit for performing a non-linear
reception demodulating process on an output from the band-limit filter 22.
The envelope detecting circuit 26 performs an envelope detection on a
signal whose band has been limited by the band-limit filter 22, and
outputs level information (direct current components, analog information)
of carrier wave components contained in the received signal. The
comparator 27 compares the level information of the direct current
components from the envelope detecting circuit 26 with a reference level
set in advance, and outputs a result of the comparison to the level
detecting unit 47 in the digital processing unit 4.
The level detecting unit 47 variably controls an amplification factor of
the variable gain amplifier 111 in the gain controlling unit 49 on the
basis of the result of the comparison relating to the direct current
components contained in the received signal inputted from the comparator
27, thereby controlling such that the signal is received with appropriate
direct current components. Namely, even when the apparatus receives a
non-linear modulated wave, it is possible to obtain a desired electric
field strength by configuring a feed-back loop similar to that employed
when a linear modulated wave is received.
In concrete, if the direct current components contained in the received
signal are above a predetermined level, the level detecting unit 47
notifies the gain controlling unit 49 of it, whereby the gain controlling
unit 49 controls the variable gain amplifier 111 to decrease a gain of the
received signal to be amplified therein and outputted therefrom. If the
direct current components contained in the received signal are below the
predetermined level, the level detecting unit 47 notifies the gain
controlling unit 49 of it, whereby the gain controlling unit 49 controls
the variable gain amplifier 111 to increase a gain of the received signal
to be amplified therein and outputted therefrom.
Therefore, the above comparator 27 is configured as a comparing circuit
which can compare an output from the envelope detecting circuit 26 with a
predetermined reference value and output a signal controlling the variable
gain amplifier 111.
The liner receiving circuit power controlling unit 42 in the digital
processing unit 4 controls to turn on power supply to the linear reception
demodulating circuit 10 when making the linear reception demodulating
circuit 10 an operative state, whereas turning off the power supply to the
linear reception demodulating circuit 10 when making the linear reception
demodulating circuit 10 an inoperative state.
Similarly, the non-linear receiving circuit power controlling unit 45 in
the digital processing unit 4 controls to turn on power supply to the
non-linear reception demodulating circuit 20-1 when making the non-linear
reception demodulating circuit 20-1 the operative state, whereas tuning
off the power supply to the non-linear reception demodulating circuit 20-1
when making the non-linear reception demodulating circuit 20-1 the
inoperative state.
In the mobile station 1 to which the two-mode demodulating apparatus 7-1
according to the first embodiment is applied, the linear receiving circuit
power controlling unit 42 and the non-linear receiving circuit power
controlling unit 45 control to make the non-linear reception demodulating
circuit 20-1 the inoperative state (power supply OFF) when making the
linear reception demodulating circuit 10 the operative state (power supply
ON), whereas controlling to make the linear reception demodulating circuit
20-1 the inoperative state (power supply OFF) when making the non-linear
reception demodulating circuit 20-1 the operative state (power supply ON),
thereby making only one system of the A/D converting function the
operative state.
Hereinafter, description will be made of an operation of the mobile station
1 to which the two-mode demodulating apparatus 7 according to the first
embodiment of this invention is applied with reference to a flowchart
shown in FIG. 5.
When a power of the mobile station 1 is turned on, the local oscillated
frequency setting unit 43 in the digital processing unit 4 sets a local
frequency of the PLL unit 30, thereby making the linear reception
demodulating circuit 10 the operative state, while making the non-linear
reception demodulating circuit 20-1 the inoperative state under controls
of the linear receiving circuit power controlling unit 42 and the
non-linear receiving circuit power controlling unit 45 (Step S1) so as to
set a mode of communication in a digital communication system.
The mobile station 1 receives a signal (pilot signal, for example) from a
base station in the vicinity to determine whether or not there is a base
station in the digital communication system in the vicinity of the mobile
station 1 (Step S2). If it is determined that there is a base station in
the digital system in the vicinity, the mobile station 1 performs a
digital communication process via that base station in the digital system
(Step S3).
Namely, the linear reception demodulating circuit 10 becomes the operative
state, the multipliers 112I and 112Q perform orthogonal detection in the
quasi-synchronous system on a received signal subjected to the automatic
gain control to convert the received signal into baseband signals in two
systems, the linear wave receiving band-limit filters 115I and 115Q and
the high-speed A/D converters 116I and 116Q convert the baseband signals
into demodulated signals as digital signals, then the linear wave
receiving circuit 41 in the digital processing unit 4 performs a
regenerating process and the like.
If there occurs no instruction to transit to an analog communication system
(from the base station in this case) during such communication in the
digital communication system (NO route at Step S4), the digital
communication process as above is continued until the end of the
communication (from NO route at Step S5 to Step S3).
If there occurs an instruction to transit to the analog communication
system from the system during the communication in the digital
communication system, the local oscillated frequency setting unit 43 in
the digital processing unit 4 changes the setting of a local frequency in
the PLL unit 30, besides the liner receiving circuit power controlling
unit 42 and the non-linear receiving circuit power controlling unit 45
control to make the linear reception demodulating circuit 10 the
inoperative state while making the non-linear reception demodulating
circuit 20-1 the operative state (from YES route at Step S4 to Step S6).
Whereby, this communication is switched to a communication process in the
analog communication system (Step S7). Incidentally, the communication
process in the analog communication system is continued until the
communication is terminated (Step S8).
In this case, the multiplier 21 converts the received signal amplified by
the variable gain amplifier 111 on the basis of the local signal from the
PLL unit 30 into a second intermediate frequency signal (that is, a signal
containing basebands in various systems), the band-limit filter 22 then
limits the bandwidth of the signal so as to allow only a signal in a
pass-band adapted to a non-linear modulation system applied as a
modulation-demodulation system to pass therethrough.
The received signal band-limited and branched is subjected to envelope
detection in the envelope detecting circuit 26, then compared with the
reference level in the comparator 27, whereby an electric field strength
is obtained by configuring a feed-back loop similar to that applied upon
linear reception.
In the above mobile station 1, if it is determined that there is no base
station in the digital communication system in the vicinity when the power
is turned on and the linear reception demodulating circuit 10 is made the
operative state, the local oscillated frequency setting unit 43 sets the
local frequency of the PLL unit 30, besides the linear reception
demodulating circuit 10 is made the inoperative state while the non-linear
reception demodulating circuit 20-1 is made the operative state under the
controls of the linear receiving circuit power controlling unit 42 and the
non-linear receiving circuit power controlling unit 45 so as to change the
mode and set it to a mode of communication in the analog communication
system (from NO route at Step S2 to Step S9).
Whereby, the mobile station 1 exchanges a signal with a base station in the
vicinity to determine whether or not there is a base station in the analog
communication system in the vicinity of the mobile station 1 (Step S10).
In this case, if there is a base station in the analog communication sy | | |
