JP2001044871A - Reception circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reception circuit where the structure of a circuit for band selection can be simplified. SOLUTION: This reception circuit is provided with 1st intermediate frequency conversion circuits 721, 723, 735, that separate a frequency band of a signal with a 1st frequency band and a signal with a 2nd frequency band from a received signal, convert the frequency of the signal with the 2nd frequency band into a frequency of a 3rd frequency band close to the 1st frequency band and convert the signal with the 1st frequency band into an intermediate frequency signal, 2nd intermediate frequency conversion circuits 722, 724, 726 that convert the signal with the 3rd frequency band from the frequency conversion means into the intermediate frequency signal, and an operation control means 727 that causes the 1st intermediate frequency conversion circuits or the 2nd intermediate frequency conversion circuits to be activated, in response to a frequency band selection signal. Thus, it is not required to switch high frequency signal, so that a switch whose configuration is made complicated to ensure isolation is not required, and the circuit configuration can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving circuit, and more particularly, to a receiving circuit for receiving broadcast signals in a plurality of frequency bands.

[0002]

2. Description of the Related Art A receiving circuit such as a DAB tuner for receiving digital audio broadcasting (DAB) has been developed. In such digital audio broadcasting, a plurality of frequency bands are provided. For example, a first frequency band having a frequency of 87.5 to 108 MHz called band 2 and frequencies 1452 to 149 called L band
This is a second frequency band of 2 MHz.

[0003] Since the frequencies of the first frequency band and the second frequency band are greatly different from each other, the receiving circuit shown in FIG. 3 is conventionally used. FIG. 3 shows a block diagram of an example of a conventional receiving circuit. In the figure, a high-frequency signal received by an antenna enters a terminal 10, and a low-pass filter (LP
F) 12 and a bandpass filter (BPF) 14. The low-pass filter 12 passes a signal having a frequency of 108 MHz or less, that is, a signal in the first frequency band, and this signal is supplied to a changeover switch 16. Bandpass filter 1
4 passes a signal in a second frequency band having a frequency of 1452 to 1492 MHz, which is supplied to a mixer 22 through an amplifier 18 and a bandpass filter 20, where it is mixed with a local oscillation signal from a local oscillator (LOSC) 24. The signal is converted into a signal of a third frequency band of, for example, a frequency of 170 to 240 MHz, and supplied to the changeover switch 16.

The changeover switch 16 is provided with a band selection signal B. The signal supplied from either the low-pass filter 12 or the mixer 22 is selected according to the SW, and supplied to the band-pass filter 26. The signal that has passed through the bandpass filter 26 is supplied to the bandpass filter 30 through the amplifier 28, where a signal having a frequency band of 87.5 to 240 MHz is extracted. This signal is supplied to the mixer 32, where the local oscillator 3
The signal is mixed with the local oscillation signal from No. 4 and frequency-converted to be a first IF signal (intermediate frequency signal) of a predetermined frequency (for example, 38.9 MHz). Here, the bandpass filters 26 and 3
0 and the local oscillator 34 output the band selection signal B.0. The pass frequency band and the local oscillation frequency are changed by switching the inductance according to the SW.

The first IF signal passes through an amplifier 36 and a SAW filter 38, and then passes through an amplifier 40 to a mixer 42.
The signal is mixed with a local oscillation signal from a local oscillator 44 and frequency-converted to be a second IF signal having a predetermined frequency. This signal is output from a terminal 50 via a bandpass filter 46 and an amplifier 48.

[0006]

A conventional receiving circuit converts a signal of a second frequency band having a frequency of 1452 to 1492 MHz into a frequency of 170 to 240 MHz adjacent to the first frequency band.
After the signal is converted into a signal of the third frequency band of z, the signal is switched using the switch 16. Since signals of the first and third frequency bands are always supplied to the changeover switch 16, the band selection signal B. When one of the signals is selected by switching the changeover switch 16 according to the SW, it is necessary to increase the isolation so that the other signal does not leak out. Becomes complicated.

The band filters 26 and 30 and the local oscillator 34 output a band selection signal B.B. The bandpass filters 26 and 30 are used to change the pass frequency band and the local oscillation frequency by switching the inductance according to the SW.
In addition, there is a problem that a switch for switching the inductance is required for each of the local oscillator 34 and the circuit structure is complicated.

[0008] The present invention has been made in view of the above points, and has as its object to provide a receiving circuit in which the structure of a circuit for performing band switching is simplified.

[0009]

According to a first aspect of the present invention, there is provided a receiving circuit for receiving a broadcast signal of a first frequency band and a broadcast signal of a second frequency band having a frequency greatly different from the first frequency band. , The first signal from the received signal
Separating means (62, 64) for separating a signal in a frequency band from a signal in a second frequency band; and separating the signal in the second frequency band from the separating means into a third frequency in the vicinity of the first frequency band. Frequency conversion means (74-82) for converting the frequency into a signal in a band, a first intermediate frequency conversion circuit (721, 723, 725) for converting the signal in the first frequency band from the separation means into an intermediate frequency signal, A second intermediate frequency conversion circuit (722, 724, 726) for converting a signal of the third frequency band from the frequency conversion means into the intermediate frequency signal
And an operation control means (727) for operating one of the first intermediate frequency conversion circuit and the second intermediate frequency conversion circuit in response to a band selection signal, wherein the first intermediate frequency conversion circuit (721, 723, 725) and an intermediate frequency signal output from the operating one of the second intermediate frequency conversion circuits (722, 724, 726) to a subsequent circuit.

As described above, according to the band selection signal, the first intermediate frequency conversion circuit (721, 723, 725) and the second intermediate frequency conversion circuit
Since either one of the intermediate frequency conversion circuits (722, 724, 726) is operated, there is no need to switch high frequency signals, and a switch having a complicated configuration for ensuring isolation can be eliminated. Since only the operation / non-operation of the first intermediate frequency conversion circuit (721, 723, 725) and the second intermediate frequency conversion circuit (722, 724, 726) is performed, the circuit structure is simplified.

Note that the reference numerals in the parentheses are provided for easy understanding, and are merely examples.

[0012]

FIG. 1 is a block diagram showing an embodiment of a receiving circuit according to the present invention. In the figure, a high-frequency signal (RF signal) received by an antenna enters a terminal 60 and is supplied to a low-pass filter (LPF) 62 and a band-pass filter (BPF) 64. The low-pass filter 62 allows signals having a frequency of 108 MHz or less to pass. The signal that has passed through the low-pass filter 62 is supplied to a band-pass filter 66, and a signal in a first frequency band of 87.5 to 108 MHz is extracted through an amplifier 68 and a band-pass filter 70. The signal of the first frequency band is supplied to the mixing circuit 72.

On the other hand, the bandpass filter 64 has a frequency of 1452.
~ 1492 MHz signal in the second frequency band,
This signal is supplied to a mixer 78 through an amplifier 74 and a bandpass filter 76, where a local oscillator (LOSC) 80
Is mixed with the local oscillating signal from the third frequency band and converted into a signal in a third frequency band of, for example, a frequency of 170 to 240 MHz. The band filter 82 removes components other than the third frequency band and supplies the signal to the mixing circuit 72. You. The mixing circuit 72 has a built-in local oscillator. SW is supplied.

FIG. 2 is a block diagram showing one embodiment of the mixing circuit 72. As shown in FIG. In FIG. 2, RF input circuits 721 and 72
2 respectively include first and third bandpass filters 70 and 82.
The RF signal of the frequency band is supplied, and the mixers 723 and 72
4 respectively. Local oscillators 725 and 726 generate local oscillation signals for the first and third frequency bands, respectively, and supply them to mixers 723 and 724, respectively.

The band switch circuit 727 has a band selection signal B. SW is supplied, and the band switch circuit 727 outputs the band selection signal B.S. A BS signal is generated according to the value of SW. When this BS signal is at a high level, for example,
The input circuit 721, the mixer 723, and the local oscillator 725 are activated and the other is deactivated. When the BS signal is low, the other RF input circuit 722, the mixer 724, and the local oscillator 726 are activated and one is deactivated. Is done.

A predetermined frequency (for example, 38.9 MH) generated by one of the mixers 723 and 724 is used.
The first IF signal (intermediate frequency signal) of z) is amplified by the amplifier 728 and output to the outside. Note that the local oscillation amplifier 7
Reference numeral 29 amplifies a local oscillation signal output from the local oscillators 725 and 726 and outputs the amplified signal to a PLL (not shown in FIG. 1).

The first IF signal output from the amplifier 728 of the mixing circuit 72 passes through the amplifier 86 and the SAW filter 88 shown in FIG. 1 and is then supplied to the mixer 92 via the amplifier 90. The signal is mixed with the oscillation signal and frequency-converted into a second IF signal having a predetermined frequency. This signal is output from the terminal 100 via the bandpass filter 96 and the amplifier 98.

In the above embodiment, instead of switching and selecting the first and third high-frequency signals with the changeover switch 16 as in the conventional circuit, the band selection signal B.R. In accordance with the BS signal corresponding to the value of SW, the RF input circuit 721 and the mixer 723
, Local oscillator 725, RF input circuit 722 and mixer 7
24 and the local oscillator 726 are selected and operated, so that the configuration of the mixing circuit 72 is simple.
In addition, the first and third high-frequency signals are sufficiently isolated.

Note that the low-pass filter 62 and the band-pass filter 64 correspond to the separating means, the amplifier 74, the band-pass filter 76, the mixer 78 and the local oscillator 80 correspond to the frequency converting means, and the RF input circuit 721 , Mixer 72
3 and the local oscillator 725 correspond to the first intermediate frequency conversion circuit, the RF input circuit 722, the mixer 724 and the local oscillator 726 correspond to the second intermediate frequency conversion circuit, and the band switch circuit 727 corresponds to the operation control means. .

[0020]

As described above, the first aspect of the present invention provides
Separating means for separating the signal of the first frequency band and the signal of the second frequency band from the received signal; and separating the signal of the second frequency band from the separating means into a signal of the second frequency band near the first frequency band. Frequency converting means for converting the frequency of the signal into signals of three frequency bands, a first intermediate frequency converting circuit for converting the signal of the first frequency band from the separating means to an intermediate frequency signal, and a third frequency band of the frequency converting means A second intermediate frequency conversion circuit for converting the signal of
Operating control means for operating one of the first intermediate frequency conversion circuit and the second intermediate frequency conversion circuit in response to a band selection signal, wherein the first intermediate frequency conversion circuit and the second intermediate frequency conversion circuit An intermediate frequency signal output from the operating one of the frequency conversion circuits is supplied to a subsequent circuit.

As described above, one of the first intermediate frequency conversion circuit and the second intermediate frequency conversion circuit is operated in accordance with the band selection signal, so that it is not necessary to switch the high frequency signal and the isolation is secured. Therefore, a switch having a complicated configuration can be dispensed with, and the circuit structure is simplified since only the operation / non-operation of the first intermediate frequency conversion circuit and the second intermediate frequency conversion circuit is switched.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a receiving circuit of the present invention.

FIG. 2 is a block diagram of one embodiment of a mixing circuit 72;

FIG. 3 is a block diagram illustrating an example of a conventional receiving circuit.

[Explanation of symbols]

 62 low-pass filter 64, 66, 70, 76, 96 band-pass filter 68, 74, 90, 98 amplifier 72 mixing circuit 78, 92, 723, 724 mixer 80, 94, 725, 726 local oscillator 88 SAW filter 721, 722 RF input circuit 727 Band switch circuit

Claims (1)

[Claims] A first frequency band broadcast signal; a first frequency band broadcast signal;
A receiving circuit for receiving a broadcast signal of a second frequency band having a frequency greatly different from a frequency band, comprising: a separating unit configured to separate a signal of the first frequency band and a signal of the second frequency band from a received signal; Frequency conversion means for frequency-converting the signal of the second frequency band from the separation means into a signal of a third frequency band near the first frequency band; and converting the signal of the first frequency band from the separation means to an intermediate frequency. A first intermediate frequency conversion circuit for converting the signal into a signal; a second intermediate frequency conversion circuit for converting a signal in the third frequency band from the frequency conversion means to the intermediate frequency signal; An operation control means for operating one of the intermediate frequency conversion circuit and the second intermediate frequency conversion circuit, wherein the first intermediate frequency conversion circuit and the second intermediate frequency conversion circuit Receiving circuit and supplying an intermediate frequency signal output from the direction that the operating subsequent circuit.