Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2000-01-10
2003-01-28
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S134000, C333S202000, C333S176000
Reexamination Certificate
active
06512427
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a spurious signal reduction circuit, and more particularly to a spurious signal reduction circuit which is provided in a main signal circuit in a high-frequency radio transmitter and receiver for a radio communication apparatus, such as a mobile station, a base station and a multiplex station, and can prevent a spurious signal from radiating and mixing.
2. Description of the Related Art
FIG. 1
shows a high-frequency radio part in a conventional radio communication apparatus. In a high-frequency transmitter
10
in the high-frequency radio part, a transmitting baseband signal is modulated by a modulator (MOD)
11
using, for example, a QPSK method into an IF signal. Next, the IF signal is amplified by an IF amplifier (IFA)
12
and a predetermined band-limited IF signal is extracted by an IF filter (IFF)
13
. Then, the predetermined band-limited IF signal is up-converted to an RF signal by an RF mixer
14
and a predetermined band-limited RF signal ft is extracted by an RF filter (RFF)
15
. Finally, the predetermined band-limited RF signal ft is power-amplified by a high power amplifier (HPA)
16
and transmitted by an antenna
41
through an antenna common part
42
.
A received RF signal from the antenna
41
is supplied to a high-frequency receiver
20
in the high-frequency radio part through the antenna common part
42
. The received RF signal is amplified by a low-noise amplifier (LNA)
21
and a predetermined band-limited RF signal fr is extracted by an RF filter (RFF)
22
. Then, the predetermined band-limited RF signal is down-converted to an IF signal by an RF mixer
23
and a predetermined band-limited IF signal is extracted by IF filters (IFF)
24
and
26
. An amplitude of the IF signal is controlled to be a constant value by a feedback loop which comprises IF amplifiers (IFA)
25
,
27
and an automatic gain control circuit (AGC)
29
. Finally, the IF signal is demodulated by a demodulator (DEM)
28
using the QPSK method into a received base-band signal.
Generally, a radio communication apparatus comprises a plurality of local oscillators and mixers in the same case. Therefore, a spurious signal fs is generated based on a cross-modulation distortion among output signals of the local oscillators and the mixers. To suppress the spurious signal fs, the high-frequency transmitter and receiver are assembled in the form of separate modules. If possible, it is desirable that each RF part and IF part is assembled in the form of a separate module. Then, each module is sufficiently shielded electrically and magnetically and the RF part and the IF part are connected by means of a coaxial cable for a main signal. However, it is basically desirable to suppress a spurious signal at its source or a mixing point.
Conventionally, in the high-frequency transmitter
10
shown in
FIG. 1
, the RF filter (RFF)
15
is provided between the RF mixer
14
and the HPA
16
to extract the predetermined band-limited RF signal ft and to suppress a radiation of the spurious signal fs. In the high-frequency receiver
20
shown in
FIG. 1
, the RF filter (RFF)
22
is provided between the LNA
21
and the RF mixer
23
to extract the predetermined band-limited RF signal fr and to prevent the RF signal fr from mixing with the spurious signal fs.
FIG. 2
shows a conventional RF filter. A construction of the RF filter in the high-frequency receiver is the same construction as in the high-frequency transmitter. FIG.
2
(A) shows an example of a construction of the RF filter using concentrated constant elements. A band-pass filter is constructed by an LC series circuit comprising an inductor L
1
and a capacitor C
1
and an LC parallel circuit comprising an inductor L
2
and a capacitor C
2
. A 2nd-order band-pass filter which has a cascade of two band-pass filters is inserted between an input terminal IN and an output terminal OUT of a main signal line. Therefore, only a main signal having a predetermined bandwidth is passed and a spurious RF signal having frequencies other than a passband of the band-pass filter is stopped.
FIG.
2
(B) shows an example of a construction of the RF filter using distributed constant elements. Strip lines
54
,
55
each having a length equal to a half wavelength &lgr;/2 of a main signal are placed between an input terminal IN and an output terminal OUT on a dielectric substrate made of GaAs or molten silica, etc., and these components are connected electromagnetically through edges of these components. The strip lines
54
,
55
operate as a resonator at the main signal frequency and they construct a band-pass filter. Therefore, only the main signal having a predetermined bandwidth is passed and a spurious RF signal having frequencies other than a pass-band of the bandpass filter is stopped.
However, when the LC series or parallel circuits are inserted in the main signal line shown in FIG.
2
(A), a loss of the main signal is increased because resistance components and conductance components are substantially inserted in the main signal line as well as the inductors L
1
and L
2
.
On the other hand, when the resonance lines
54
,
55
each having the length &lgr;/2 are placed as shown in FIG.
2
(B), a loss of the main signal is increased due to a conductor loss &agr;
C
, a dielectric loss &agr;
D
and a radiation loss &agr;
R
. Especially, over a frequency range between 30 GHz to 40 GHz, the radiation loss &agr;
R
from the resonance lines
54
,
55
can not be ignored and this causes a reduction of a Q value. As a result, the strip lines
54
,
55
can not operate as a resonator.
Therefore, in the conventional high-frequency radio apparatus, for a transmitter, a loss of the main signal and power consumption are large and a gain is reduced. On the other hand, for a receiver, a noise figure and a gain are reduced.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a spurious signal reduction circuit in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a spurious signal reduction circuit which can prevent a spurious signal from radiating and mixing without a loss of a main signal.
The above objects of the present invention are achieved by a spurious signal reduction circuit which is connected to a main signal line. The spurious signal reduction circuit comprises a resistor having a terminal connected to the main signal line, an LC parallel resonance circuit and an LC series resonance circuit. The parallel resonance circuit has a resonance frequency which is equal to a main signal frequency and has a terminal connected to another terminal of the resistor. The series resonance circuit has a resonance frequency which is equal to a spurious signal frequency and has a terminal connected to the other terminal of the resistor.
REFERENCES:
patent: 3881137 (1975-04-01), Thanawala
patent: 4701947 (1987-10-01), Stader
patent: 5023866 (1991-06-01), De Muro
patent: 868344 (1941-12-01), None
patent: 54-51758 (1979-04-01), None
patent: 1-144824 (1989-06-01), None
patent: 1334224 (1987-08-01), None
Bettendorf Justin P.
Fujitsu Limited
Katten Muchin Zavis & Rosenman
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