Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Reexamination Certificate
1999-07-20
2002-09-24
Trost, William (Department: 2746)
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
C455S142000, C455S180100, C455S188100, C455S191100
Reexamination Certificate
active
06456832
ABSTRACT:
TECHNICAL FIELD
The present invention is related to an antenna circuit for effectively transferring an antenna output signal outputted from an antenna to a receiver.
BACKGROUND OF THE INVENTION
In
FIG. 4
, there is shown an example of a conventional antenna circuit provided in a base terminal unit of an AM/FM receiving antenna. In
FIG. 4
, an antenna output signal of an AM/FM receiving antenna
10
is subdivided into two antenna output signals. One antenna output signal is supplied to an FM band filter
12
, an output signal derived from this FM band filter
12
is supplied to an FM amplifying circuit
14
, and furthermore, an amplified FM signal outputted from the FM amplifying circuit
14
is supplied to an FM receiver
16
. Also, the other divided antenna output signal is supplied to an AM band filter
18
, an antenna output signal outputted from this AM band filter
18
is supplied to an AM amplifying circuit
20
, and furthermore, an amplified AM signal outputted from the AM amplifying circuit
20
is supplied to an AM receiver
22
. These FM band filter
12
, FM amplifying circuit
14
, AM band filter
18
, and AM amplifying circuit
20
are provided in either the base terminal unit of the AM/FM receiving antenna
10
or the unit near this AM/FM receiving antenna
10
. The amplified output signals of the FM amplifying circuit
14
and the AM amplifying circuit
20
are transferred via a cable to both the FM receiver
16
and the AM receiver
22
in a proper manner, respectively.
In the FM band filter
12
, an input terminal to which the antenna output signal is supplied is connected to an output terminal via a series-connected circuit made by sequentially connecting a capacitor Cl, two coils L
1
, L
2
, and another capacitor C
2
in a serial manner. Then, the FM band filter
12
is arranged by connecting a junction point between the two coils L
1
and L
2
via a parallel circuit of a capacitor C
3
and a coil L
3
to the ground.
Also, the FM amplifying circuit
14
to which the FM band signal filtered through the FM band filter
12
is supplied is arranged as follows: In other words, an input terminal is connected via a capacitor C
4
to a base of a transistor Tr
1
. This base is grounded via a resistor R
1
, and also is connected via a resistor R
2
to one terminal of a parallel-connected circuit made of a resistor R
3
and a capacitor C
5
. The other terminal of this parallel-connected circuit is connected to a collector of the transistor Tr
1
. This collector is connected via a capacitor C
6
to the output terminal. Also, this collector is connected via a series-connected circuit of a coil L
4
and a resistor R
4
to a power supply terminal “+B”. A junction point between this coil L
4
and a resistor R
4
is grounded via a capacitor C
7
. Furthermore, an emitter of the transistor Tr
1
is grounded via a parallel-connected circuit made of a resistor R
5
and a capacitor C
8
.
Furthermore, the AM band filter
18
is so arranged that an input terminal to which the antenna output signal is supplied is connected via a coil L
5
to an output terminal, and this output terminal is grounded via a capacitor C
9
.
In this arrangement, the FM band filter
12
may block the AM band signal and may pass the FM band signal therethrough by properly set the constants of the circuit structural elements. Then, the FM amplifying circuit
14
constitutes the emitter grounded type transistor circuit in which the radio (high) frequency load is provided at the collector of the transistor Tr
1
, and is operable as a voltage amplification type amplifying circuit. As a result, the FM band signal which has passed through the FM band filter
12
is voltage-amplified by the voltage amplification effect of this transistor Tr
1
, and then, the voltage-amplified FM band signal is outputted. Also, in the circuit arrangement of this FM amplifying circuit
14
, the input impedance is made substantially equal to the output impedance, and the output impedance of the AM/FM receiving antenna
10
via the FM band filter
12
is matched with the input impedance of the FM receiver
16
.
In this arrangement, the AM band filter
18
may block the FM band signal and may pass the AM band signal therethrough by properly set the constants of the circuit structural elements. Only the AM band signal is amplified by the AM amplifying circuit
20
to output the amplified AM band signal.
On the other hand, in the above-explained conventional FM amplifying circuit
14
, the voltage of the FM band signal functioning as the input signal to be amplified is applied between the base of the transistor Tr
1
and the emitter thereof, and furthermore, the voltage of the amplified output signal is applied between the collector of the transistor Tr
1
and the emitter thereof. Then, when both the input signal and the output signal are increased, the amplification characteristic defined by the amplifying capability and the bias condition of the transistor Tr
1
exceeds a pre-selected range indicative of the linearity, so that high frequency (radio frequency) distortions and cross modulation distortions would occur. Then, this input/output signal amplitude characteristic is indicated by a circle symbol in
FIG. 2
under such a condition that the amplitude of the output signal is saturated with respect to the increase of the amplitude of the input signal. Accordingly, there is such a problem that the cross modulation distortion is strengthened under such high electric fields as a place near an FM broadcasting signal transmission station, and therefore, radio interference would occur.
Also, as shown in FIG.
5
(
a
), assuming now that as FM band signals of high electric fields, for example, two broadcasting waves
1
and
2
having frequencies of 76 MHz and 76.6 MHz are present, these broadcasting waves
1
and
2
are applied to the AM amplifying circuit
20
without being sufficiently attenuated/blocked by the AM band filter
18
. As a result, as shown in FIG.
5
(
b
), the second-order cross modulation wave of 600 KHz equal to a frequency difference between the two broadcasting waves
1
and
2
is also amplified by the AM amplifying circuit
20
to output the amplified second-order cross modulation wave. This 600 KHz signal is contained in the frequency range of the AM band signal, and may function as the interference wave in the AM receiver
22
.
Furthermore, conventionally, as the AM/FM receiving antenna
10
, such an antenna having a physical length of approximately 1 m is generally used. Thus, the antenna output signal having the practically high level with respect to the AM band signal could be obtained from this general-purpose antenna. On the other hand, since a strong demand is recently made of compact antennas, there is such a trend that as to the AM/FM receiving antenna
10
, a shorter antenna is used by employing a helical coil and the like, while the antenna effective length is equal to approximately 1 m with respect to the FM band signal, but the antenna physical length is made shorter than, or equal to 50 cm. Thus, although the antenna output signal for the FM band signal could be obtained at the substantially same level as that of the conventional antenna, the level of the AM band signal would be largely reduced. As a result, this may cause a serious problem. That is, the attenuation of the AM band signal by the FM band filter
12
cannot be neglected. This is because the coils L
1
and L
3
which constitute the FM band filter
12
own the small impedances with respect to the AM band signal, and the AM band signal is largely attenuated via the capacitor C
1
, as represented in the equivalent circuit diagram shown in FIG.
3
(
b
). Thus, since the AM band signal supplied the AM band filter
18
is reduced, there is such a problem that the reception sensitivity with respect to the AM band signal would be largely deteriorated.
DISCLOSURE OF THE INVENTION
The present invention has an object to provide an antenna circuit capable of improving deterioration of an amplification characteristic thereof under high electric
Horie Ryo
Imai Junichi
Kagoshima Yuichi
Kameda Shozaburo
Uchida Haruhisa
Le Danh
Trost William
Yokowo Co., Ltd.
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