Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Reexamination Certificate
1998-04-30
2002-10-08
Cumming, William (Department: 2684)
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
C455S011100, C455S063300, C455S236100, C455S447000
Reexamination Certificate
active
06463268
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio receiver.
2. Description of the Related Art
The conventional technique disclosed, for example, U.S. Pat. No. 5,020,147 “FM/AM broadcast signal converter” correspondent to the Japanese Patent Application Laid-open No. 1-273432) mentions that an FM broadcast receiver can be integrated into one chip to adopt the direct conversion system instead of the superheterodyne system.
FIG. 1
illustrates one example of such a receiver, in which the FM intermediate frequency is 150 kHz, the part surrounded by a chain line is integrated into one chip as an IC
10
, and the components or circuits placed outside the chain line are connected to the IC
10
from outside, thus forming a receiver.
And, of the outside components or the outside circuits, the symbol
41
indicates an antenna, the symbol
42
a pre-selector (band pass filter) of which pass band is the FM band, the symbol
43
indicate a resonant circuit for a local oscillator, which is formed of a coil and variable capacitor, and the symbol
44
indicates a speaker.
Upon reception of an FM broadcast signal, the signal received by the antenna
41
is supplied to mixing circuits
12
I and
12
Q through the signal line of the pre-selector
42
and a radio frequency amplifier
11
. Here, suppose that the objective received signal SRX is given by:
SRX=A
sin &ohgr;
RXt,
&ohgr;RX=2&pgr;fRX.
And, in the subsequent signal processing, only the relative amplitude and phase of the signals are involved; and in the description of the foregoing equation and the following, the initial phase of the signals will be omitted.
And, assuming that the local oscillation frequency is given by:
fLO=fRX−fIF
fIF: FM intermediate frequency (=150 kHz), a local oscillation circuit
21
generates a local oscillation signal SLO having double the frequency of the original local oscillation frequency fLO.
And, the signal SLO is supplied to frequency dividing circuits
22
I,
22
Q and the frequency is divided into half. As shown in
FIG. 5
, for example, the frequency dividing circuits
22
I,
22
Q generate signals SLI, SLQ, respectively, that reverse at a zero-crossing point in the rising phase and at a zero-crossing point in the falling phase. That is, the signal SLO is divided into the signals SLI, SLQ having the frequency fLO and the phase difference of 90° between the two, expressed as:
SLI
=
B
cos
ω
LO
SLQ
=
B
sin
ω
LO
ω
LO
=
2
π
fLO
.
Incidentally, in the description of the foregoing equation and the following, only the fundamental components (SLI and SLQ) will be expressed as to the SLI SLQ SLQ for simplification, and the harmonics of them will be omitted.
These signals SLI, SLQ are supplied to the mixing circuits
12
I,
12
Q, respectively, as the local oscillation signals.
Therefore, output signals SII, SIQ of the mixing circuits
12
I,
12
Q will be given by the following.
SII
=
SRX
·
SLI
=
A
sin
ω
RXt
×
B
cos
ω
LO
=
α
{
sin
(
ω
RX
+
ω
LO
)
t
+
sin
(
ω
RX
-
ω
LO
)
t
}
SIQ
=
SRX
·
SLQ
=
A
sin
ω
RXt
×
B
sin
ω
LO
=
α
{
-
cos
(
ω
RX
+
ω
LO
)
t
+
cos
(
ω
RX
-
ω
LO
)
t
}
α
=
A
·
B
/
2
And, as described later, the signal components of the angular frequency (&ohgr;RX+&ohgr;LO) are removed from these signals SLI, SLQ, and the signal components of the angular frequency (&ohgr;RX−&ohgr;LO) are used as the intermediate frequency signal; and for simplicity, ignoring the signal components of the angular frequency (&ohgr;RX+&ohgr;LO) in the foregoing equation will produce the following.
SII
=
α
sin
(
ω
RX
-
ω
LO
)
t
SIQ
=
α
cos
(
ω
RX
-
ω
LO
)
t
And
,
here
the
image
signal
Sim
is
given
by
Sim
=
C
sin
ω
imt
ω
im
=
ω
LO
+
ω
IF
ω
IF
=
2
π
fIF
,
and if the received signal SRX from the pre-selector
42
contains the image signal Sim, the signals SII, SIQ in this case are expressed by the following equations.
SII
=
α
sin
(
ω
RX
-
ω
LO
)
t
+
β
sin
(
ω
im
-
ω
LO
)
SIQ
=
α
cos
(
ω
RX
-
ω
LO
)
t
+
β
cos
(
ω
im
-
ω
LO
)
t
b
=
A
·
C
/
2
Further, the following relation is given in this case:
&ohgr;RX<&ohgr;LO<&ohgr;im,
and therefore, the foregoing equations are expressed as follows.
SII
=
αsin
(
ω
RX
-
ω
LO
)
t
+
β
sin
(
ω
im
-
ω
LO
)
=
-
α
sin
(
ω
LO
-
ω
RX
)
t
+
β
sin
(
ω
im
-
ω
LO
)
SIQ
=
α
cos
(
ω
RX
-
ω
LO
)
t
+
β
cos
(
ω
im
-
ω
LO
)
t
=
α
cos
(
ω
LO
-
ω
RX
)
t
+
β
cos
(
ω
im
-
ω
LO
)
t
And, these signals SII, SIQ are supplied to phase shifting circuits
13
I,
13
Q. The phase shifting circuits
13
I,
13
Q are configured with, for example, active filters using capacitors, resistors, and operational amplifiers. The phase shifting circuit
13
I shifts the phase of the signal SII &phgr; by and the phase shifting circuit
13
Q shifts the phase of the signal SIQ by (&phgr;+90°). Thereby, the phase shifting circuits
13
I,
13
Q maintain the phase difference between the two inputted signals SII, SIQ within 90°±1° in a required intermediate frequency band.
Thus, the signal SIQ advances in phase by 90° compared to the signal SII due to phase shifting circuits
13
I,
13
Q. The signals SII, SIQ are transformed into:
SII
=
-
α
sin
(
ω
LO
-
ω
RX
)
t
+
b
sin
(
ω
im
-
ω
LO
)
t
SIQ
=
α
cos
{
(
ω
LO
-
ω
Cumming William
Maioli Jay H.
Sony Corporation
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