Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
1998-09-01
2001-05-15
Urban, Edward F. (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S254000
Reexamination Certificate
active
06233442
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a high frequency apparatus having an adjusting element.
A conventional high frequency apparatus will be explained hereinafter. As shown in
FIG. 8
, the conventional high frequency apparatus has been constructed to comprise an input terminal
1
to which a high frequency signal is input, a bandpass filter
2
connected to the input terminal
1
, an unbalance-balance converter
3
connected to an output of the bandpass filter
2
, a balanced mixer
6
one input of which an output of the unbalance/balance converter
3
is connected to and other input of which an output of a voltage-controlled oscillator
4
is connected to via a buffer
5
, an intermediate frequency filter
7
connected between both outputs of the balanced mixer
6
, a balance-unbalance converter
8
connected to the intermediate frequency filter
7
, an output terminal
9
connected to an output of the balance-unbalance converter
8
, a known PLL circuit
10
connected to the voltage-controlled oscillator
4
, for controlling an oscillation frequency of the voltage-controlled oscillator
4
, and a data input terminal
11
for supplying local oscillation frequency designating data to the PLL circuit
10
. In addition, in order to adjust this high frequency device, test terminals
12
,
13
are provided to both ends of the intermediate frequency filter
7
respectively.
An operation of the high frequency apparatus constructed as above will be explained hereinbelow. A high frequency signal input from the input terminal
1
is passed through the bandpass filter
2
. The high frequency signal passed through the bandpass filter
2
is mixed with an output signal of the voltage-controlled oscillator
4
, which is decided by the PLL circuit
10
according to a signal input from the data input terminal
11
, by the balanced mixer
6
and then a signal having a sum or difference frequency is output from the balanced mixer
6
. In other words, the high frequency signal input from the input terminal
1
can be tuned based on a data signal input from the data input terminal
11
. A signal having a frequency bandwidth of 54.25 MHz to 58.75 MHz can be selected by passing the output of the balanced mixer
6
through the intermediate frequency filter
7
, then converted into an unbalanced output by the succeeding balance-unbalance converter
8
, and then output from the output terminal
9
.
The bandpass filter
2
is a high frequency filter which consists of an inductance and a capacitance and has a passband characteristic shown as a characteristic
41
in FIG.
9
A. The high frequency signal is waveform-shaped to have such passband characteristic
41
. The intermediate frequency filter
7
is composed of a parallel circuit of an inductance
14
and a capacitance
15
and has a passband characteristic shown as a characteristic
42
in FIG.
9
B. The intermediate frequency signal is waveform-shaped to have such passband characteristic
42
. However, since the bandpass filter
2
and the intermediate frequency filter
7
are connected in series with each other, an output waveform output from the output terminal
9
can be given by a synthesized waveform shown as a characteristic
43
in FIG.
3
C. Because of an influence of the intermediate frequency filter
7
, it has been difficult to adjust the bandpass filter
2
while monitoring such synthesized waveform
43
, i.e., obtain the characteristic
41
shown in FIG.
9
A. Therefore, after both ends
12
,
13
of the intermediate frequency filter
7
have been short-circuited and dumped by a contactor pin
17
having a dumping resistor
16
so as to eliminate the influence of the intermediate frequency filter
7
, the bandpass filter
2
has been adjusted while monitoring the output waveform output from the output terminal
9
.
However, according to the above configuration, the influence of the intermediate frequency filter
7
has not been able to be completely eliminated because of variations of a length of the contactor pin
17
and the dumping resistor
16
, a contact resistance of the contactor pin
17
, or the like. As a consequence, an adjusting error of the bandpass filter
2
serving as the high frequency filter has been caused.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the above problem and it is an object of the present invention to provide a high frequency apparatus in which the adjusting error of the high frequency filter can be reduced.
According to the present invention, a high frequency apparatus comprises: an input terminal, a high frequency filter to which a signal input into the input terminal is supplied, a mixer one input of which an output signal of the high frequency filter is supplied to and an other input of which an output signal of a local oscillator is supplied to, an intermediate frequency filter to which an output signal of the mixer is supplied, an output terminal to which an output signal of the intermediate frequency filter is supplied, and an electronic switch provided in a vicinity of the intermediate frequency filter. The electronic switch makes a passband characteristic of the intermediate frequency filter substantially flat by closing both contacts, wherein opening and closing of the electronic switch is controlled externally. Since the electronic switch is disposed in the vicinity of the intermediate frequency filter, the high frequency apparatus can be provided which includes no uncertain element like the contactor pin in the conventional devices and includes small adjusting error of the high frequency filter.
Further, since opening and closing of the electronic switch is carried out indirectly by the control signal externally, influence upon the high frequency signal passing through the intermediate frequency filter can be extremely reduced.
Moreover, there is no need of employing the contactor pin because the output terminal can be employed, so that production facilities can be simplified and also lower cost of the production facilities can be achieved.
Further, in the high frequency apparatus of the present invention, the mixer, local oscillator, and electronic switch are incorporated in a same integrated circuit. Since the electronic switch can be disposed in vicinity of a signal transmission line by building the electronic switch in the integrated circuit, the influence upon the high frequency signal passing through the intermediate frequency filter can be extremely reduced and they can be installed in the same integrated circuit. Hence, cost of the electronic switch can be reduced to a negligible extent and lower cost can be attained as a whole.
Furthermore, the high frequency apparatus of the present invention further comprises a PLL circuit connected to the local oscillator, oscillation frequency of the local oscillator is controlled by a signal which is input into the PLL circuit via a data input terminal and opening and closing of the electronic switch is also controlled. Since the control signal of the electronic switch can be derived from the data control terminal, there is no necessity of providing a control terminal for the electronic switch in the integrated circuit particularly. Also, since control of the electronic switch can be performed by the signal derived from the data control terminal, a testing contactor pin can be omitted and thus defective contact caused by the contactor pin can be eliminated. Further, since the contactor pin can be omitted, a testing jig can be reduced in size and a lower cost can be achieved.
Moreover, in the high frequency apparatus of the present invention, a balanced mixer is employed as the mixer, the intermediate frequency filter is connected between outputs of the balanced mixer, and a dumping resistor and the electronic switch are connected in series across both ends of the intermediate frequency filter. Since the balanced mixer is employed as the mixer, the high frequency apparatus is excellent in preventing external noises and is suited for the integrated circuit. In addition, the high frequency fi
Koda Tsutomu
Matsushita Seiji
Mishima Akira
Ozaki Tetsuya
Jackson Blane J.
Matsushita Electric - Industrial Co., Ltd.
Pearne & Gordon LLP
Urban Edward F.
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