Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
1998-03-23
2001-05-22
Bost, Dwayne (Department: 2744)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S250100, C455S193100, C455S254000
Reexamination Certificate
active
06236842
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio receiver comprising an antenna tuning circuit whose tuning frequency is improved.
2. Description of the Related Art
In general, when a radio receiver receives disturbance stations fud
1
, fud
2
having a strong field intensity, in addition to an object station fd which the radio receiver desires to receive the stations fd, fud
1
, fud
2
having frequencies different from one another by an equal extent (see FIG.
3
(i)), the receiver generates various harmonic signals according to the non-linear element characteristics of an amplifying element, such as a transistor, of an RF amplifier thereof. Those harmonic signals may have frequencies corresponding to the addition or difference of the frequencies of object and disturbance stations fu, fud
1
, fud
2
.
If the frequency of such a harmonic signal is equal to that of the object station or the intermediate frequency, the harmonic signal may cause mutual modulation disturbance to the object station.
FIG. 5
is a diagram showing a circuit structure of a conventional radio receiver which is less affected by mutual modulation disturbance because an antenna tuning circuit
1
is employed.
Referring to
FIG. 5
, a received RF signal is supplied to an antenna tuning circuit
1
, which is then tuned to the object station and outputs a signal into an RF amplifier
2
for amplification. After amplification, the signal is then supplied to an RF tuning circuit
3
, which is then tuned and outputs a signal into a mixing circuit
4
. In the mixing circuit
4
, the signal is rendered to frequency conversion using a local oscillation signal supplied by a local oscillation circuit
5
and converted into an IF (intermediate frequency) signal. The IF signal is then output to an IF amplifier
6
for amplification, and subsequently to an FM detection circuit
7
for FM detection.
It should be noted that the mixing circuit
4
supplies an IF signal also to a field strength detection circuit
8
. In the circuit
8
, the peak level of the supplied IF signal is detected to thereby know the field intensity of the relevant received signal. The circuit
8
then supplies a signal based on the detection result to a dumping control circuit
9
. The circuit
9
in turn detects whether or not the supplied signal is higher than a predetermined level, and outputs a signal based on the detection result to a dumping circuit
10
to thereby turn on/off the dumping circuit
10
.
In the above procedure, if disturbance stations fud
1
, fud
2
having high field intensity are also received together with an object station fd, the field strength detection circuit
8
outputs a higher than a predetermined level signal. Accordingly, the dumping control circuit
9
outputs a signal a. In response to this signal a, a current flows into PIN diodes
10
a
and
10
b
in the dumping circuit
10
.
When a current flows in the PIN diodes
10
a
and
10
b
, the resistance values thereof become smaller, so that the receiving line is AC grounded via the PIN diode
10
a
, whereby the dumping circuit
10
is turned on (ON state).
As described above, since a received RF signal is partly grounded when the dumping circuit
10
is in an ON state, an output signal level from the antenna tuning circuit
1
is attenuated, so that the subsequent RF amplifier
2
receives a reduced level signal. As a result, a harmonic signal level is reduced, and mutual modulation disturbance is resultantly suppressed, the harmonic signal being generated based on object and disturbance stations according to the non-linear characteristics of elements in the RF amplifier
2
.
In addition to the above, the antenna tuning circuit
1
is adjusted to have a tuning frequency so as to match the frequency of an object station (see the solid line in
FIG. 3
(i)) by thus adjusting the characteristics of a coil
1
a
and a capacitor
1
b
and the capacity of a varicap diode
1
c
. Specifically, the capacity of a varicap diode
1
c
is adjusted according to the frequency of an object station in response to a control signal generated by a control circuit
11
. With this adjustment, the antenna tuning circuit
1
is tuned to the frequency of an object station and those in the vicinity thereof.
However, when the dumping circuit
10
is once turned on and a DC blocking capacitor
10
c
is thereby connected in parallel to the capacitor
1
b
and the varicap diode
1
c
, the tuning frequency of the antenna tuning circuit
1
is caused to be shifted toward a lower frequency side (see the dot line in
FIG. 3
(i) ) by an extent corresponding to the added capacity of the DC blocking capacitor
10
c
. In particular, if disturbance stations fud
1
, fus
2
are present on the lower frequency side with respect to the object station fd (see
FIG. 3
(i)), the level of a signal relative to an object station becomes lower than that of the disturbance fud
1
, fud
2
, when the dumping circuit
10
is turned on. Thereby, the level of a harmonic signal based on the disturbance stations fud
1
, fud
2
, is relatively increased. As a result, mutual modulation disturbance may become worse.
SUMMARY OF THE INVENTION
The present invention has been conceived to overcome the above problems and aims to provide a radio receiver capable of reducing mutual modulation disturbance caused due to operation of a dumping circuit.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a radio receiver, comprising an antenna tuning circuit to be tuned to an RF signal; a dumping circuit attenuating the RF signal or an output signal from the antenna tuning circuit; an RF amplifier amplifying an output signal of the antenna tuning circuit; a dumping control circuit having the dumping circuit operate when the RF signal is at a more than predetermined level; and a corrector means removing influences of the dumping circuit over the antenna tuning circuit.
According to a second of the invention, in the radio receiver according to the first aspect, the corrector means generates a correction signal for correcting a tuning frequency of the antenna tuning circuit so as to match to a frequency of an object station when the dumping circuit is turned on.
According to a third aspect of the invention, in the radio receiver according to the second aspect, the tuning frequency of the antenna tuning circuit is corrected by a fixed extent.
According to a fourth aspect of the invention, in the radio receiver according to the second aspect, the tuning frequency of the antenna tuning circuit is corrected by an extent determined according to a frequency of object station.
According to a fifth aspect of the invention, in the radio receiver according to the fourth aspect, the tuning frequency of the antenna tuning circuit is corrected by an extent determined according to a frequency region among a number of frequency regions to which a frequency of a received object station belongs, the number of frequency regions being obtained by predivision of a frequency receiver band.
As described above, according to the present invention, when an RF signal exceeds a predetermined level and a dumping circuit is thus turned on, the tuning frequency of an antenna tuning circuit is corrected so as to be tuned to the frequency of a received object station.
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Bost Dwayne
Cantor Coburn LLP
Persino Raymond B.
Sanyo Electric Co,. Ltd.
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