JP2000174653A - Radio receiver for double conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio receiver of a double conversion system provided with high reception sensitivity and excellent interference characteristics. SOLUTION: This radio receiver is provided with an up converter part 6 for converting reception signals to first intermediate frequency signals, a down converter part 9 for converting the first intermediate frequency signals converted in the up converter part 6 to second intermediate frequency signals, a tuner circuit A for amplifying and detecting the second intermediate frequency signals converted in the down converter part 9 and outputting them as audio signals and a control circuit B for controlling the tuner circuit A. Also, an antenna tuning circuit 3 provided with a tuning coil 20 and a variable capacitance diode 21 is provided in the tuner circuit A and the control circuit B inputs a control voltage corresponding to a desired reception frequency to the antenna tuning circuit 3, changes the capacity of the variable capacitance diode 21 and tunes the antenna tuning circuit 3 to the radio waves of the desired frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver of a double conversion system, and more particularly to a radio receiver of a double conversion system having an antenna tuning circuit.

[0002]

2. Description of the Related Art Conventionally, a radio receiver of a double conversion system as shown in a block diagram of FIG. 2 has been proposed. This radio receiving apparatus receives a radio wave transmitted from a broadcasting station by an antenna 1 and transmits the received radio wave to an RF amplifier 2
The high-frequency reception signal is removed by the low-pass filter 35, and the reception signal RF that has passed through the low-pass filter 35 is input to the first mixer circuit 5, where the oscillation signal OS1 of the first local oscillation circuit 4 is 10.7 mixed
It is converted into a first intermediate frequency signal IF1 of MHz. The converted first intermediate frequency signal IF1 is input to the second mixer circuit 8, which supplies 10.2
An oscillation signal OS2 of 10.25 MHz output from the second local oscillation circuit 7 based on the clock of the crystal oscillator 17 of 5 MHz is input, mixed with the first intermediate frequency signal IF1, and mixed with the second intermediate frequency signal IF2 of 450 KHz. The converted second intermediate frequency signal IF2 is amplified by the second intermediate frequency signal amplifier 10 and then detected by the detection circuit 11 and output as an audio signal. It is widely used because of its excellent cost performance.

[0003]

However, the above-mentioned double-conversion radio receiver employs an antenna non-tuning in which a received signal received by an antenna is higher than a frequency band to be received by a low-pass filter. For this reason, radio waves of other broadcast stations besides the desired broadcast station are also input to the tuner circuit, and are susceptible to other radio waves, thus causing problems in sensitivity and interference characteristics.

An object of the present invention is to solve the above-mentioned problems and to provide a radio receiver of a double conversion system having high reception sensitivity and excellent interference characteristics.

[0005]

In order to solve the above-mentioned problems, a double-conversion-type radio receiving apparatus according to the present invention comprises a first local oscillation circuit and a first mixer circuit, and receives radio waves received by an antenna. And a second local oscillator circuit and a second mixer circuit. The first intermediate frequency converted by the up-converter section is converted into a second intermediate frequency. A radio converter having a down-converter section, a tuner circuit for amplifying and detecting the second intermediate frequency signal output from the down-converter section, and outputting the audio signal as an audio signal; and a control circuit for controlling the tuner circuit. In the apparatus, an antenna tuning having a tuning coil and a variable capacitance diode between the antenna and the tuner circuit. Path, the control circuit inputs a control voltage corresponding to a desired reception frequency to the antenna tuning circuit, changes the capacity of the variable capacitance diode, tunes a radio wave of a desired frequency to the antenna tuning circuit, It is characterized in that it is inputted to the first mixer circuit.

[0006]

FIG. 1 is a block diagram showing a double conversion type radio receiving apparatus (hereinafter, referred to as a radio receiving apparatus) according to the present invention. The antenna 1 receives a radio wave transmitted from a broadcasting station. An RF amplifier 2 for amplifying a radio wave received by an antenna 1, an antenna tuning circuit 3 for tuning to a reception frequency of the received radio wave and separating a radio wave of a desired frequency, a first local oscillation circuit 4, and a first mixer An up-converter section 6 for converting a reception frequency tuned by the antenna tuning circuit 3 into a first intermediate frequency; a second local oscillation circuit 7 and a second mixer circuit 8
A down-converter section 9 for converting the first intermediate frequency converted by the up-converter section 6 to a second intermediate frequency, and converting the second intermediate frequency signal converted by the down-converter section 9 into a second intermediate frequency signal. It comprises a tuner circuit A for amplifying by the frequency signal amplifier 10, detecting by the detection circuit 11 and outputting as an audio signal, and a control circuit B for controlling the tuner circuit A.

The antenna tuning circuit 3 is an LC tuning circuit having a tuning coil 20 and a variable capacitance diode 21, and tunes to a desired broadcast station frequency by changing the DC voltage applied to the variable capacitance diode 21 to change the capacitance. The tuned reception signal RF can be extracted, and the applied DC voltage is supplied from the control circuit B.

The tuner circuit A comprises a first local oscillation circuit 4 and a first mixer circuit 5, and adjusts the frequency of the received signal RF received by the antenna 1 to a first intermediate frequency (10.7).
The first intermediate frequency signal IF1 converted by the up-converter unit 6 is composed of an up-converter unit 6 for converting the first intermediate-frequency signal IF1 into a first intermediate frequency signal IF1, and a second local oscillator circuit 7 and a second mixer circuit 8. Second intermediate frequency (450K
Hz), a second intermediate frequency signal amplifier 10 for converting the second intermediate frequency signal IF2 converted by the down converter 9 into a second intermediate frequency signal IF2, and an amplified second And a detection circuit 11 for detecting the intermediate frequency signal IF2 and outputting the audio signal as an audio signal. The tuner circuit may be constituted by a tuner LSI formed as an IC.

The control circuit B includes a PLL circuit, an A / D converter, a D / A converter, a memory, a counter, an I / O
A key switch 15 for selecting a desired broadcasting station, a display device 16 such as an LCD for displaying the frequency of the selected broadcasting station, etc., are connected. A control signal (control voltage) VT2 for separating the frequency of the station is output to the antenna tuning circuit 3 so as to tune to a desired broadcast station radio wave. The control circuit B
Is not limited to a microcomputer, but a DSP (Digital S) specialized in digital signal processing.
signal processor).

In FIG. 1, reference numeral 22 denotes a level shifter, which may be provided when the power supply voltage of the control circuit (microcomputer) is 5 V or 3 V or the like, and when the voltage of VT2 is required more.

According to the radio receiver having the above configuration, when the operator operates the key switch 15 to set the frequency of the broadcast station desired to be heard, the set frequency is displayed on the LCD 16 as a display device. Then, a control voltage VT2 corresponding to the set frequency is output from the control circuit B, and the output control voltage VT2 is applied to the variable capacitance diode 21 of the antenna tuning circuit 3, and the capacitance of the variable capacitance diode 21 corresponds to the applied voltage. As a result, the tuning frequency can be tuned to the frequency of the broadcast station desired to be heard, and the received signal RF of that frequency is input to the first mixer circuit 5. The control voltage VT2 is designed based on a CV characteristic curve (see FIG. 2) indicating the relationship between the capacitance of the variable capacitance diode and the voltage, and a table 26 of frequency versus control voltage data is created in the memory 25 in advance. The control voltage data corresponding to the frequency of the broadcasting station selected by the key switch 15 is read from the table 26, and the read control voltage data is read by the DA converter 27 to the control voltage VT2.
Can be converted to

When it is desired to tune the tuning characteristics strictly with the control voltage of VT2, VT2 may be controlled until the maximum output of the S meter 30 of the tuner circuit A is reached, as shown in FIG. The receiving frequency may be sought in advance, the VT2 at which each frequency takes the maximum value may be stored in the peak hold memory 31, and the VT2 may be read from the peak hold memory 31 and used again during reception.

On the other hand, the control circuit B comprises a first local oscillation circuit 4
Outputs the control voltage VT1. The control voltage VT1 is a variable capacitance diode (not shown) of the first local oscillation circuit 4.
To generate an oscillation signal OS1 having the sum of the frequency of the reception signal RF and the frequency of the first intermediate frequency signal IF1 (10.7 MHz), and input the same to the first mixer circuit 5 together with the reception signal RF. You. This control voltage VT1 is
OSC frequency (10.7MHz + fi) counter 2
8 and a so-called frequency PLL circuit configuration (PLL circuit 29) so that the control voltage V becomes 10.7 MHz.
What is necessary is just to supply T1.

The first mixer circuit 5 converts the input received signal RF into a 10.7 MHz first intermediate frequency signal IF1 and outputs it. This first intermediate frequency signal IF1 is input to the second mixer circuit 8. Since the 10.25 MHz oscillation signal OS2 generated by the second local oscillation circuit 7 based on the 10.25 MHz crystal oscillator 17 clock is input to the second mixer circuit 8, the second local oscillation The oscillation signal OS2 of the circuit 7 and the first intermediate frequency signal IF1
And converted into a second intermediate frequency signal IF2 of 450 KHz. The second intermediate frequency signal IF2 is amplified by the second intermediate frequency amplifier 10, detected by the detection circuit 11 and output as an audio signal.

As described above, the received radio wave received by the antenna can be tuned to the frequency of the broadcasting station desired by the antenna tuning circuit, so that a specific frequency is input to the first mixer circuit. As in the case of the down-conversion tuner, radio waves and noises of other broadcasting stations do not enter the tuner circuit, so that a receiving device with improved sensitivity characteristics and excellent interference characteristics can be realized.

[0016]

According to the radio receiving apparatus of the present invention, after the reception signal received by the antenna is tuned to the frequency of the broadcasting station selected by the antenna tuning circuit, only the reception signal of the tuned specific frequency is output. Since it is input to the tuner circuit,
As compared with a conventional double-conversion-type radio receiving apparatus that inputs a received signal to a tuner circuit through a low-pass filter, a radio receiving apparatus having high reception sensitivity and excellent interference characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram of a radio receiving apparatus according to the present invention.

FIG. 2 is a CV characteristic diagram of a variable capacitance diode.

FIG. 3 is a block diagram illustrating another example of the radio receiving apparatus.

FIG. 4 is a block diagram of a conventional radio receiving apparatus.

[Explanation of symbols]

 Reference Signs List 3 antenna tuning circuit 4 first local oscillation circuit 5 first mixer circuit 6 up converter section 7 second local oscillation circuit 8 second mixer circuit 9 down converter section 20 tuning coil 21 variable capacitance diode A tuner circuit B control circuit

Claims (1)

[Claims] 1. A first local oscillation circuit and a first mixer circuit, wherein the frequency of a radio wave received by an antenna is adjusted to a first frequency.
An up-converter section for converting to an intermediate frequency; and a down-converter section comprising a second local oscillator circuit and a second mixer circuit for converting the first intermediate frequency converted by the up-converter section to a second intermediate frequency. A radio receiver having a tuner circuit for amplifying and detecting the second intermediate frequency signal output from the down-converter unit and outputting the audio signal as an audio signal; and a control circuit for controlling the tuner circuit. An antenna tuning circuit having a tuning coil and a variable capacitance diode is provided between the tuner circuit and the tuner circuit.The control circuit inputs a control voltage corresponding to a desired reception frequency to the antenna tuning circuit, Radio waves of a desired frequency are tuned to the antenna tuning circuit by changing the capacitance, and the first mixer Radio receiver of the double conversion system for causing inputted to over circuit.