JPH06310941A - Frequency conversion integrated circuit and bidirectional communication device using this integrated circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] It is an object of the present invention to provide an integrated circuit for frequency conversion in a two-way communication device such as a cordless telephone, which can correctly perform frequency conversion even during strong input. [Structure] A first input terminal 11, a mixing circuit 12 to which the first input terminal 11 is connected to one input, and a first output terminal 13 to which an output of the mixing circuit 12 is connected,
Voltage controlled oscillator circuit 1 whose oscillation frequency is controlled by voltage
9, a second output terminal 17 to which the output of the voltage controlled oscillator circuit 19 is connected, and a third input terminal 15 to which a signal is supplied to the other input of the mixing circuit 12. Is.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency conversion integrated circuit used in a bidirectional communication device and a bidirectional communication device using the integrated circuit.

[0002]

2. Description of the Related Art A conventional frequency conversion integrated circuit will be described below.

As shown in FIG. 3, a conventional frequency conversion integrated circuit includes an input terminal 1 connected to an antenna, a mixing circuit 2 having one input connected to the input terminal 1, and a mixing circuit 2. A first output terminal 3 to which the output is connected, a voltage controlled oscillator circuit 5, a coupling circuit 6 to which the output of the voltage controlled oscillator circuit 5 is coupled, and the other input of the coupling circuit 6 and the mixing circuit 2. A frequency conversion integrated circuit was configured with the buffer circuit 7 connected between and. Here, the coupling circuit 6 is a general integrated circuit and often uses an integrated capacitance of about several pF.

A demodulation circuit is connected to the first output terminal 3, and the output of the demodulation circuit is connected to the speaker. A second input terminal is connected to the voltage controlled oscillator circuit 5.

The operation of the frequency conversion integrated circuit configured as described above will be described below. As a conventional example, a cordless telephone slave unit has a reception frequency of 380 MHz.
Consider the case of 11F21.7 MHz.

The 380 MHz band signal input from the antenna was input to the input terminal 1, frequency-converted to 21.7 MHz by the mixing circuit 2, and output from the first output terminal 3. Then, this signal was demodulated by a demodulation circuit provided outside the frequency conversion integrated circuit. At this time, the voltage controlled oscillator circuit 5 oscillates in the 359 MHz band in order to set the output of the mixing circuit 2 to 21.7 MHz.

[0007]

However, in such a conventional configuration, the mixing circuit 2 and the mixing circuit 2 are provided in the same integrated circuit.
The coupling circuit 6 and the buffer circuit 7 are provided, and when the isolation characteristics of the buffer circuit, the coupling circuit, etc. are not appropriate, for example, at the time of strong input, the signal input to the input terminal 1 is the same as that of the mixing circuit 2 and the buffer circuit. Since the voltage controlled oscillator circuit 5 is suppressed through the coupling circuit 7 and the coupling circuit 6, the oscillation frequency of 359 MHz of the voltage controlled oscillator circuit 5 is the input frequency 3
It will be modulated at 80 MHz. As a result, the output from the mixing circuit 2 has a problem that a correct output signal of 21.7 MHz cannot be obtained.

The present invention solves such a problem and an object thereof is to provide a frequency conversion integrated circuit for correctly frequency converting even if a strong input signal is input to the input terminal. .

[0009]

To achieve this object, a frequency conversion integrated circuit according to the present invention comprises a first input terminal and a mixing circuit in which the first input terminal is connected to one input. , A first output terminal to which the output of the mixing circuit is connected, a voltage-controlled oscillation circuit whose frequency is controlled by the voltage applied to the second input terminal, and the output of the voltage-controlled oscillation circuit are connected The second output terminal and the third input terminal to which a signal is supplied to the other input of the mixing circuit are provided.

[0010]

With this structure, a coupling circuit can be connected between the second output terminal and the third input terminal outside the integrated circuit. Therefore, using a bandpass filter that passes only the output of the voltage controlled oscillator circuit in the coupling circuit,
Alternatively, the insulation between the oscillation circuit and the mixing circuit can be made high by using a capacitor suitable for the used frequency or by shielding the input and output of this coupling circuit. That is, since the signal applied to the input terminal does not affect the voltage controlled oscillator circuit, the frequency can be correctly converted even if a strong input is input.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram of a bidirectional communication device according to an embodiment of the present invention. The bidirectional communication device of the present invention includes a high-frequency signal input / output terminal 22 to which an antenna 21 is connected, a first bandpass filter 23 connected to the high-frequency signal input / output terminal 22, and the first bandpass filter. A frequency conversion circuit 24 to which the output of 23 is connected, a demodulation circuit 25 to which the output of the frequency conversion circuit 24 is connected, and an output of this demodulation circuit 25 are connected, and an audio output in which a signal is guided to an external speaker 27. Terminal 26
And a voice input terminal 29 to which the microphone 28 is connected
And the modulation circuit 30 connected to the audio input terminal 29.
An output amplification circuit 31 to which the output of the modulation circuit 30 is connected, and a second bandpass filter 32 connected between the output of the output amplification circuit 31 and the high frequency signal input / output terminal 22. The frequency conversion circuit 24 is composed of the following frequency conversion integrated circuit. still,
Some microphones are provided with a frequency deviation limiting circuit, a confidential circuit, etc. between the microphone 28 and the voice input terminal 29.

That is, as shown in FIG. 1, the frequency conversion integrated circuit 24 has a first input terminal 11, a mixing circuit 12 to which the first input terminal 11 is connected to one input, and the mixing circuit 12. First output terminal 13 to which the output is connected
And the voltage controlled oscillator circuit 19 and the voltage controlled oscillator circuit 1
9 is connected to the second output terminal 17, and the other input of the mixing circuit 12 is provided with a third input terminal 15 to which a signal is supplied via the buffer circuit 14. A coupling circuit 18 is connected between the third input terminal 15 and the second output terminal 17 outside the frequency conversion integrated circuit 24.

The operation of the frequency conversion integrated circuit configured as described above will be described below.

3 input from the antenna 21 in the figure
The 80 MHz band (hereinafter referred to as RF frequency) signal is input to the frequency conversion circuit 24 via the first band pass filter 23. Here, this frequency conversion circuit 24 is constituted by the frequency conversion integrated circuit of the present invention as shown in FIG. That is, the RF frequency is input from the first input terminal 11 and is input to one input of the mixing circuit 12.

Further, the voltage controlled oscillator circuit 19 is 359 MHz.
It oscillates in the band (hereinafter, local frequency). This output is the second
From the output terminal 17 of the third input terminal 15 to the third input terminal 15.
From the input terminal 15 of the mixer circuit 1 through the buffer circuit 14
2 is input to the other input terminal. Mixing circuit 12 here
Then, the frequency is converted to 21.7 MHz (hereinafter referred to as IF frequency), and the result is output to the first output terminal 13. This output signal is thereafter output as sound by the speaker 27 via the demodulation circuit 25 shown in FIG.

Here, the coupling circuit 18 is constituted by a bandpass filter for removing the RF frequency and passing only the local frequency, thereby attenuating the RF signal and increasing the isolation, and to the voltage controlled oscillator circuit 19 at the time of strong input. Repression can be improved.

As a result, the voltage controlled oscillator circuit 19 can stably oscillate even with a strong input signal input from the antenna 21.

Even when the local frequency of the voltage controlled oscillator circuit 19 is changed, the coupling circuit 18 can be constituted by a bandpass filter whose center frequency is adjusted to the local frequency.

Further, by disposing the ground terminal 16 between the third input terminal 15 and the second output terminal 17, the isolation between the third input terminal 15 and the second output terminal 17 is achieved. Can be better.

Further, as a simple method, the coupling circuit 18 can be composed of a capacitor. Specifically, when the master unit RF frequency is 380 MHz, the coupling circuit 18 is set to 2
By using a pF capacitor, the isolation between the third input terminal 15 and the second output terminal 17 can be ≧ 35 dB.

Also, in the case of the handset RF frequency of 254 MHz band, the third input terminal 15 and the second output terminal 17 are formed by forming the coupling circuit 18 with a 1.5 pF capacitor.
The isolation between and can be ≧ 35 dB.

As described above, by using the same frequency conversion integrated circuit, the isolation between the third input terminal 15 and the second output terminal 17 can be increased to perform frequency conversion in different RF frequency bands. . Further, by including the frequency conversion integrated circuit as described above, it is possible to realize a bidirectional communication device that operates stably with respect to a strong input.

[0023]

As described above, in the frequency conversion integrated circuit of the present invention, the first input terminal, the mixing circuit in which the first input terminal is connected to one input, and the output of the mixing circuit are A signal is output to the first output terminal connected to the voltage control oscillation circuit whose oscillation frequency is voltage controlled, the second output terminal connected to the output of the voltage control oscillation circuit, and the other input of the mixing circuit. And a third input terminal to which a coupling circuit is provided, and a coupling circuit can be provided outside the integrated circuit between the second output terminal and the third input terminal.

Therefore, it is possible to enhance the insulation between the oscillation circuit and the mixing circuit by using a bandpass filter for passing only the output of the voltage controlled oscillation circuit in this coupling circuit or by shielding the input and output of this coupling circuit. The strong input characteristics can be improved in a wide frequency range as much as possible, and the degree of freedom in design can be expanded.

That is, since the signal applied to the input terminal does not affect the voltage controlled oscillator circuit, the frequency can be correctly converted even if a strong input is input.

[Brief description of drawings]

FIG. 1 is a block diagram of an integrated circuit for frequency conversion according to an embodiment of the present invention.

FIG. 2 is a block diagram of a bidirectional communication device using the frequency conversion integrated circuit of the present invention.

FIG. 3 is a block diagram of a conventional frequency conversion integrated circuit.

[Explanation of symbols]

 11 First Input Terminal 12 Mixing Circuit 13 First Output Terminal 15 Third Input Terminal 17 Second Output Terminal 18 Coupling Circuit 19 Voltage Controlled Oscillation Circuit 20 Second Input Terminal

Claims (3)

[Claims] 1. A first input terminal, a mixing circuit in which the first input terminal is connected to one input, a first output terminal in which the output of the mixing circuit is connected, and a second input. A voltage-controlled oscillation circuit whose frequency is controlled by the voltage applied to the terminal, a second output terminal to which the output of the voltage-controlled oscillation circuit is connected, and a third circuit for supplying a signal to the other input of the mixing circuit.
And an integrated circuit for frequency conversion having an input terminal. 2. The frequency conversion integrated circuit according to claim 1, wherein a ground terminal or a high frequency ground terminal is provided between the second output terminal and the third input terminal. 3. A high frequency signal input / output terminal, a first bandpass filter connected to this high frequency signal input / output terminal, a frequency conversion circuit to which the output of this first bandpass filter is connected, and this frequency. Connected to the demodulation circuit to which the output of the conversion circuit is connected, the audio output terminal to which the output of this demodulation circuit is connected and which leads the signal to the external speaker, the audio input terminal to which the microphone is connected, and this audio input terminal And a second band-pass filter connected between the output of the output amplifier circuit and the high-frequency signal input / output terminal. The frequency conversion circuit comprises the frequency conversion integrated circuit according to claim 1 or 2, and a coupling circuit is connected between the second output terminal and the third input terminal of the frequency conversion integrated circuit. Continued two-way communication device.