Demodulator and receiver

Details Demodulator and receiver Demodulator and receiver

2002-10-04

2004-03-30

Bayard, Emmanuel (Department: 2631)

Pulse or digital communications

Receivers

Angle modulation

Reexamination Certificate

active

06714602

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a demodulator of a direct conversion system effective for impedance measurement in a high frequency band such as the GHz band used in for example communication apparatuses for sending and receiving high frequency signals etc. and a receiver using the same.
BACKGROUND ART
FIG. 1
is a circuit diagram of the configuration of a key portion of a general demodulator.
As shown in
FIG. 1
, a demodulator
10
comprises as main components a local signal generation circuit
11
, +45 degree phase shifter
12
, −45 degree phase shifter
13
, and RF mixers
14
and
15
.
In the demodulator
10
, a local signal Slo having a predetermined frequency generated by the local signal generation circuit
11
is shifted in phase by 45 degrees by the +45 degree phase shifter
12
to be supplied to the RF mixer
14
and is shifted by −45 degrees by the −45 degree phase shifter
13
to be supplied to the RF mixer
15
.
Further, a reception signal Sr, for example, passed through a not shown antenna element or a low noise amplifier is supplied to the RF mixers
14
and
15
, the reception signal Sr and the local signal shifted in phase by exactly +45 degrees are multiplied at the RF mixer
14
to obtain an in-phase signal (I), and the reception signal Sr and the local signal shifted in phase by exactly −45 degrees are multiplied in the RF mixer
15
to obtain a quadrature signal (Q).
In the demodulator
10
using a mixer as shown in
FIG. 1
, however, use for broadband applications is difficult, and it is necessary to apply a high local level to the mixer. Further, since the mixer is in a nonlinear operating state by high local power, there is a disadvantage that it is difficult to attain low distortion demodulation.
Therefore, in recent years, a six-port type demodulator (multi-port demodulator) using a power detection circuit (power detector) and based on a different principle from that in
FIG. 1
has been proposed.
A six-port type demodulator can more easily be used for broadband applications due to the power detection circuit compared with the mixer used in the above modulation system. From this, it can be the that a multi-port demodulator has good compatibility with software radio requiring multiband or broadband characteristics. Further, there has been a tendency to use higher frequencies as the carrier frequency in wireless communication in recent years, so it is possible to deal with demands for higher frequencies as well.
Further, in a demodulation system using a mixer, a high local level has to be applied to the mixer. As opposed to this, in the multi-port system, the power detection circuit operates in a linear region. Accordingly, with the multi-port system, demodulation is possible even with a low local signal power.
Furthermore, with a demodulation system using a mixer, the mixer is in a nonlinear operating state due to the high local power. As opposed to this, with the multi-port system, the power detection circuit operates in a linear region. Accordingly, the multi-port system enables low distortion demodulation.
Below, three examples of the six-port demodulator will be explained with reference to
FIG. 2
to FIG.
4
.
FIG. 2A
is a block diagram of a first example of the configuration of a six-port demodulator. (See Document [1]: Ji Li et al.: “Dual Tone Calibration of Six-port Junction and Its Application to the Six-port Direct Digital Millimetric Receiver”, IEEE Trans. On MTT, Vol. MTT-44, No. 1, 1996.)
The six-port demodulator
20
comprises, as shown in
FIG. 2A
, quadrature hybrid circuits
21
to
24
, a branch circuit
25
, an attenuator
26
, power detection circuits (power detectors)
27
to
30
, and a resistance element R
21
.
In the six-port demodulator
20
, a reception signal Sr and a local signal S
10
are received at the quadrature hybrid circuit
21
and the signals jSr+Slo and Sr+jSlo are generated. Further, the signal jSr+Sl
0
is branched by the branch circuit
25
and supplied to the quadrature hybrid circuits
22
and
23
, while the signal Sr+jSl
0
is supplied to the quadrature hybrid circuit
23
via the attenuator
26
.
In the quadrature hybrid circuit
22
, the signals −Sr+jSlo and Sr+jSlo are generated and supplied respectively to the power detection circuit
27
and the quadrature hybrid circuit
24
. Further, in the quadrature hybrid circuit
23
, the signals j
2
S
r
and j
2
S
lo
are generated and supplied to the quadrature hybrid circuit
24
and the power detection circuit
30
. The two output signals of the quadrature hybrid circuit
24
are respectively supplied to the power detection circuits
28
and
29
.
In the power detection circuits
27
to
30
, for example, the envelope curve levels or power levels of the input signals are detected and output as signals P
21
to P
24
, respectively.
The baseband output signals, that is, detection signal P
21
to P
24
, by the power detection circuits
27
to
30
are, as shown in
FIG. 2B
, input to a multi-port signal-IQ signal conversion circuit
31
, where they are converted into the in-phase signal (I) and quadrature signals (Q) included in the reception signal and output.
FIG. 3A
is a block diagram of a second example of the configuration of a six-port demodulator. (See Document [2]: Kangasmaa, et.al.: “Six-port Direct Conversion Receiver”, European Microwave Conference 1997.)
The six-port demodulator
40
comprises, as shown in
FIG. 3A
, a branch circuit
41
, a quadrature hybrid circuit
42
, ring hybrid circuits
43
and
44
, power detection circuits (power detectors)
45
to
48
, and a resistance element R
41
.
In the six-port demodulator
40
, the reception signal Sr is branched by the branch circuit
41
and supplied to the ring hybrid circuits
43
and
44
. Further, the local signal Slo is performed predetermined quadrature processing in the quadrature hybrid circuit
42
and supplied to the ring hybrid circuits
43
and
44
.
In the ring hybrid circuit
43
, the signals Sr+Slo and Sr-Slo are generated based on the input reception signal and the local signal and supplied respectively to the power detection circuits
45
and
46
. Further, in the ring hybrid circuit
44
, the signals Sr+jSlo and Sr−jSlo are generated based on the input reception signal and the local signal and supplied respectively to the power detection circuits
47
and
48
.
Then, in the power detection circuits
45
to
48
, for example, the envelope curve levels or power levels of the input signals are detected and output as the signals P
41
to P
44
, respectively.
The baseband output signals, that is, detection signals P
41
to P
44
, by the power detection circuits
45
to
48
are, as shown in
FIG. 3B
, input to a multi-port signal-IQ signal conversion circuit
49
, where they are converted into the in-phase signal (I) and quadrature signal (Q) included in the reception signal and output.
FIG. 4
is a block diagram of a third example of the configuration of a six-port demodulator. (See Document [3]: EP97122438.1 (Dec. 18, 1997).)
The six-port demodulator
50
comprises couplers
51
and
52
, branch circuits
53
and
54
, a phase shifter
55
, power detection circuits
56
to
59
, resistance elements R
51
and R
52
, and a six-port signal-IQ signal conversion circuit
60
.
In the six-port demodulator
50
, a reception signal Sr is input by the coupler
51
to the branch circuit
53
and a part thereof is input to the power detection circuit
56
. The reception signal input to the branch circuit
53
is branched into two signals. One of the branched signals is input to the power detection circuit
57
, while the other signal is input to the phase shifter
55
. In the phase shifter
55
, a phase shift &thgr; is given to the reception signal by the branch circuit
53
, the phase shifted signal is input to the branch circuit
54
, and branched into two signals there. In the branch circuit
54
, one of the branched signals is input to the power detect

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