Receiver

Details Receiver Receiver

2000-06-27

2004-03-30

Ghayour, Mohammad H. (Department: 2631)

Pulse or digital communications

Receivers

Angle modulation

C455S205000

Reexamination Certificate

active

06714604

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wide-band receiver which receives intended system bands in batch and selects a channel by means of digital processing.
2. Related Art Statement
Research and development on various radio communication systems have been conducted in the field of data transmission and the like lately to deal with the increase of an amount of information to be transmitted and to accommodate to characteristics of each radio communication system. Such plurality of radio communication systems transmit a plurality of channels mixedly.
FIG. 1A
is a circuit diagram showing the related art of a receiver which receives and demodulates data of one communication system among such various radio communication systems. This device has been disclosed in First Document (P. R. Gray and R. G. Mayer, “Future directions of Silicon IC's for RF personal communications,” Proc. Custom Integrated Circuits Conference '95, pp. 83-90, 1995).
The signal received by the device of
FIG. 1A
is what data is multiplexed and transmitted by modulating into a high-frequency signal band by orthogonal axes (I, Q axes). A high-frequency signal (RF signal) of such high frequency fRF is inducted at an antenna
1
. The band of the RF signal is limited by a band-pass filter
2
which is an RF filter and is supplied to analog mixers
3
and
4
which compose an orthogonal demodulating section.
A local oscillator
5
outputs a local oscillating output whose oscillating frequency fC is fixed to a phase shifter
6
to convert the RF signal into a base-band signal. The phase shifter
6
shifts the phase of the local oscillating output by &pgr;n/2 and supplies the local oscillating outputs which are orthogonal to each other to the mixers
3
and
4
. The mixers
3
and
4
convert the frequency to that of the base-band by multiplying the inputted RF signal with the local oscillating outputs.
The outputs of the mixers
3
and
4
are limited by analog low-pass filters
7
and
8
and are supplied to analog multipliers
9
through
12
which compose an orthogonal demodulating section. A local oscillating output from a local oscillator
13
is phase-shifted by &pgr;/2 by a phase shifter
14
and is inputted to the multipliers
9
through
12
. The local oscillating frequency fCK of the local oscillator
13
is variable. That is, the local oscillating output from the local oscillator
13
is set at frequency for demodulating a communication system (channel) to be selected.
The multipliers
9
and
11
multiply the local oscillating output which is orthogonal each other to the output of the low-pass filter
7
and the multipliers
10
and
12
multiply the local oscillating output which is orthogonal each other to the output of the low-pass filter
8
. An I axis signal may be obtained by adding the outputs of the multipliers
9
and
10
by an analog adder
15
and a Q axis signal may be obtained by adding the outputs of the multipliers
11
and
12
by an analog adder
16
. Image components may be rejected by the adding process of the adders
15
and
16
.
Analog low-pass filters
17
and
18
limit the band of the outputs of the adders
15
and
16
and supply them to A/D converters
19
and
20
. The A/D converters
19
and
20
convert the analog signals of the I and Q axes into digital I and Q signals and output them.
FIG. 1B
is a block diagram representing the circuit diagram of FIG.
1
A.
That is, as it is apparent by comparing
FIG. 1A
with
FIG. 1B
, an RF filter
21
corresponds to the band-pass filter
2
, an orthogonal demodulating section
22
corresponds to the mixers
3
and
4
and filters
7
and
8
, a fixed local oscillating section
23
corresponds to the local oscillator
5
and the phase shifter
6
, an orthogonal demodulating section
24
corresponds to the multipliers
9
through
12
, a variable local oscillating section
25
corresponds to the local oscillator
13
and the phase shifter
14
, an image rejecting section
26
corresponds to the adders
15
and
16
, a channel selecting section
27
corresponds to the filters
17
and
18
and an A/D converter section
28
corresponds to the A/D converters
19
and
20
.
That is, the device shown in
FIG. 1B
is arranged so as to select a desirable wave by the analog channel selecting section
27
after rejecting the image component of the output of the orthogonal demodulating section
24
by the image rejecting section
26
and to output by converting it into digital signals by the A/D converter section
28
.
However, the image rejecting precision is low due to the incompleteness of the analog circuit of the mixers
3
and
4
, the filters
7
and
8
, the phase shifter
6
and the analog multipliers
9
,
10
,
11
and
12
. Further, such arrangement lacks flexibility in changing bands and cutoff in correspondence to a plurality of systems because the filters composing the channel selecting section
27
are analog filters
17
and
18
.
FIG. 2A
is a circuit diagram showing another exemplary related art of such receiver. This device has been disclosed in Second Document (J. Crols and M. Steyaert, “A single-chip 900 MHz CMOS receiver front-end with a high performance low-IF topology” IEEE J. Solid-State Circuits, vol. 30, No. 12, pp. 1483-1492, 1995).
FIG. 2B
is a block diagram representing the circuit diagram of FIG.
2
A. The device in
FIGS. 2A and 2B
is characterized in that A/D converters
31
and
32
which correspond to an A/D converter section
46
are provided before multipliers
33
through
36
which correspond to an orthogonal demodulating section
47
. The oscillating frequency fC of a local oscillator
30
is variable. The local oscillator
30
composing a variable local oscillating section
45
outputs an oscillating output of oscillating frequency corresponding to a channel to be selected. This oscillating frequency sets the output of the mixers
3
and
4
at frequency corresponding to fixed oscillating frequency fCK of a local oscillator
37
composing a fixed local oscillating section
48
.
The outputs of the low-pass filters
7
and
8
are converted into digital signals by the A/D converters
31
and
32
and are then supplied to the digital multipliers
33
through
36
composing an orthogonal demodulating section
47
. The oscillating output of the local oscillator
37
whose phase has been shifted by &pgr;/2 by a phase shifter
38
is given to the digital multipliers
33
through
36
. Signals of I and Q axes may be obtained by the multipliers
33
through
36
. The output of the multipliers
33
and
34
and the output of the multipliers
35
and
36
are subtracted respectively by adders
39
and
40
composing an image rejecting section
49
and rejected image components are supplied to low-pass filters
41
and
42
. The digital low-pass filters
41
and
42
composing a channel selecting section
50
output by limiting the band of the signals of I and Q axes.
The frequency of the variable local oscillating section
45
(local oscillator
30
) is changed in selecting a desirable channel in this arrangement. That is, it is provided with the function of selecting a channel by the orthogonal demodulating section
22
and the variable local oscillating section
45
. However, because the variable local oscillating section
45
is an analog high-frequency oscillator, it has been difficult to change the frequency programmably and to vary the frequency per channel interval across a wide-band. Further, because the oscillating frequency of the local oscillator
30
exists within the band of the desirable channel in this arrangement, it has been unable to provide the RF filter
21
, differing from the case of
FIGS. 1A and 1B
.
Accordingly, the image rejecting degree which has been realized by the RF filter
21
cannot be obtained, thus degrading the image rejecting degree of the whole receiver system.
FIG. 3A
is a circuit diagram showing another exemplary related art of the receiver. This device has been disclosed in Third Document (J. Crols and M. Steya

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