JP2003347900A - Variable band-pass filter circuit and communication apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable band-pass filter circuit which conduct communications in a comparatively broad frequency band, is inexpensive, and can be realized using a simple configuration, and to provide a communication apparatus using the same. <P>SOLUTION: The circuit consists of a variable low-pass filter circuit 2, in which a resonator for blocking a band and a variable capacitance element are combined, a variable by-pass filter circuit 4, and a broad-band amplifier 3 arranged between both the filter circuits. In this circuit, a signal-passing band for allowing only the desired signal to pass is formed between cut-off frequencies of both the filter circuits, and a communication system switching terminal 7 for applying a communication system switching voltage 88 to the variable capacitance element, corresponding to a plurality of radio communication systems is provided. With this constitution, the center frequencies and bandwidths corresponding to the plurality of radio communication systems are made variable. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference wave suppression device for removing unnecessary interference signals formed in an RF section of a software defined radio capable of supporting a plurality of communication systems, and relates to a relatively wide band frequency band. The band has a signal pass band that allows only a desired signal obtained by combining a low-pass filter circuit and a high-pass filter circuit, and has a control function for varying the center frequency and bandwidth of the signal pass band according to the communication system. The present invention relates to a band variable filter circuit and a communication device using the same.

[0002]

2. Description of the Related Art Attention has been focused on a software defined radio capable of supporting a plurality of radio communication systems by downloading software to hardware using a digital signal processing device such as a DSP or a CPU.

FIG. 8 is a block diagram showing an example of a conventionally proposed software defined radio. In FIG. 1, three wireless communication systems can be transmitted and received. For example, a PHS communication system (1.9 GHz band) 1
00, WCDMA communication system (2 GHz band) 101,
A wireless LAN communication system (2.4 GHz band) 102 or the like is conceivable.

[0004] The operation will be briefly described. At the time of reception, the RF signals input from the antennas 103 to 105 are filtered by band-pass filters (BPF) 106 to 108 to remove unnecessary interference signals and pass only desired signals. , A low noise amplifier (LN) via transmission / reception switching circuits 109 to 111.
A) After amplifying the signals at 112 to 114, the mixer circuit 118
Is input to

In the mixer circuit 118, the input RF signal and the local oscillation signal generated by the local oscillation circuit 119 are down-converted to an intermediate frequency or a baseband frequency, and the A / D converters 120 to 122 convert the analog signal into a digital signal. The signal is converted into a signal, and demodulation and digital signal processing are performed in the DSP 126.

At the time of transmission, the digital signal modulated by the DSP 126 is converted from a digital signal to an analog signal by the D / A converters 123 to 125 and input to the mixer circuit 118. In the mixer circuit 118,
The analog signal and the local oscillation signal generated by the local oscillation circuit 119 are up-converted into RF signals, and the power amplifiers (PA) 115 to 117 amplify the RF signals.
Transmission / reception switching circuits 109-111, BPFs 106-10
8. Transmit the signal via the antennas 103 to 105. The CPU 127 controls the operation of the wireless unit.

[0007]

As described above, in a software defined radio, hardware corresponding to a plurality of radio communication systems is required. Therefore, in the conventionally proposed hardware, it is necessary to use an antenna and a BPF of a frequency corresponding to each wireless communication system, and there is a problem that the circuit of the software radio RF unit is complicated and expensive. .

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to realize a variable-bandwidth filter circuit that can be realized with an inexpensive and simple configuration capable of communicating in a relatively wide frequency band and a communication apparatus using the same. Is to provide.

[0009]

In order to achieve the above object, a first means of the present invention is to provide a variable low-pass filter circuit, a variable high-pass filter circuit, and a combination of a resonator for blocking a band and a variable capacitance element. It comprises a wide band amplifier arranged between both filter circuits, forms a signal pass band for passing only a desired signal between cutoff frequencies of both filter circuits, and a communication system switching voltage corresponding to a plurality of wireless communication systems. Is applied to the variable capacitance element, and a center frequency and a bandwidth corresponding to the plurality of wireless communication systems are made variable.

According to a second aspect of the present invention, in the first aspect, a surface acoustic wave resonator is used as the resonator.

According to a third aspect of the present invention, in the first aspect, a dielectric resonator is used as the resonator.

According to a fourth aspect of the present invention, in the first aspect, an LC resonator is used as the resonator.

According to a fifth aspect of the present invention, there is provided a communication apparatus using the band variable filter circuit according to any one of the first to fourth aspects.

A sixth means of the present invention comprises a variable low-pass filter circuit combining a resonator for blocking a band and a variable capacitance element, a variable high-pass filter circuit, and a wide-band amplifier disposed between both filter circuits. Forming a signal pass band for passing only a desired signal between cutoff frequencies of both filter circuits, and a communication system switching terminal for applying a communication system switching voltage to the variable capacitance element corresponding to a plurality of wireless communication systems. Variable bandwidth filter circuit, and a CPU for generating a communication system switching voltage corresponding to a plurality of wireless communication systems.
A switching voltage corresponding to the wireless communication system from U is applied to a communication system switching terminal of the band variable filter circuit, and the center frequency and the bandwidth of the signal passband are variably based on the wireless communication system switching voltage. It is characterized by doing.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a variable-bandwidth filter circuit used in the RF transceiver of the software defined radio according to the first embodiment.

In FIG. 1, a band variable filter circuit 1 is shown.
Is composed of a variable low-pass filter circuit 2, a wideband low-noise amplifier circuit 3, and a variable high-pass filter circuit 4.
Therefore, when the RF high-frequency signal input from the wideband antenna 5 passes through the variable low-pass filter circuit 2, unnecessary signals input to frequencies higher than the desired signal are removed. After amplification, unnecessary signals input to the lower frequency side of the desired signal with respect to the desired signal are removed by the variable high-pass filter circuit 4 and output from the RF high-frequency signal output terminal 6.

The variable low-pass filter circuit 2 includes surface acoustic wave resonators 8 and 9 and coils 17 and 18, a variable capacitance diode 12,
13, and capacitors 24 and 25. The communication system switching voltage input from the communication system switching terminal 7 is supplied to the variable capacitance diode 12 via the resistors 37 and 38.
13 to determine the cutoff frequency and trap frequency of the low pass filter.

The wide band low noise amplifier circuit 3 includes a transistor 34, coils 19 and 20, capacitors 26 to 29,
It comprises resistors 35 and 36 and a transistor voltage application terminal 42. The signal input from the broadband antenna 5 is amplified to compensate for the gain of the signal attenuated by the variable low-pass filter circuit 2 and the variable high-pass filter circuit 4 and to prevent impedance interference between the respective filter circuits.

The variable high-pass filter circuit 4 includes surface acoustic wave resonators 10 and 11, coils 21 to 23, and a variable capacitance diode 1 arranged in parallel with a signal line.
4 to 16 and capacitors 30 to 33. The communication system switching voltage input from the communication system switching terminal 7 is applied to the variable capacitance diode 1 via the resistors 39 to 41.
4 to 16 to determine the cutoff frequency and trap frequency of the high-pass filter.

The principle of operation of the band variable filter circuit 1 will be described with reference to FIGS. FIG. 2 shows a low-pass filter characteristic 50 of the variable low-pass filter circuit 2 of FIG. The variable low-pass filter circuit 2 has the configuration shown in FIG.
If the communication system switching voltage is applied and the communication system switching voltage is relatively low as described in the above, as can be seen from the variable capacitance diode characteristics in FIG. Cutoff frequency 5
1 and the trap frequency 52 transition to a lower frequency. If the communication system switching voltage is relatively high, the capacitances of the variable capacitance diodes 12 and 13 become relatively small, and the cutoff frequency 51 and the trap frequency 52 shift to higher frequencies.

FIG. 3 shows a high-pass filter characteristic 60 of the variable high-pass filter circuit 4 of FIG. As described with reference to FIG. 1, the variable high-pass filter circuit 4 receives the communication system switching voltage, and if the communication system switching voltage is relatively low, as can be seen from the variable capacitance diode characteristics in FIG. 16 becomes relatively large, and the cutoff frequency 61 and the trap frequency 62 shift to lower frequencies. If the communication system switching voltage is relatively high, the variable capacitance diodes 14 to
16 becomes relatively small, and the cutoff frequency 61 and the trap frequency 62 shift to higher frequencies.

FIG. 4 shows the overall filter characteristic 70 of the variable-bandwidth filter circuit 1. This total filter characteristic 70
Is a characteristic obtained by combining the low-pass filter characteristic 50, the high-pass filter characteristic 60, and the gain component of the signal amplified by the wideband low-noise amplifier 3. Cutoff frequency 51, trap frequency 52 and cutoff frequency 61, trap frequency 62
As described with reference to FIGS. 1 to 3, the frequency shifts in the same direction with respect to the communication system switching voltage input from the communication system switching terminal 7. Bandwidth can be secured. In addition, by changing the characteristics of the variable capacitance diodes 12 to 16, the bandwidth of the comprehensive filter characteristic 70 can be set to be wider or narrower depending on the type of the communication system.

FIG. 6 is a block diagram of a software defined radio apparatus using the band variable filter circuit 1 shown in FIG. In the figure, a signal of a desired wireless communication system is transmitted from a wideband antenna 5 to a variable bandpass filter circuit 2, a transmission / reception switching circuit 81, a wideband low noise amplifier circuit 3, and a variable highpass filter circuit 4. , And removes unnecessary interference signals, passes only desired signals, and is input to the reception mixer circuit 82.

In the receiving mixer circuit 82, the intermediate frequency or the baseband frequency is down-converted by the desired signal output from the band variable filter circuit 1 and the local oscillation signal generated by the wide band local oscillation circuit 84.
The signal is converted from an analog signal to a digital signal by the A / D converter 85, and demodulation and digital signal processing are performed in the DSP 126.

The CPU 127 outputs a wireless communication system switching voltage 88 corresponding to each wireless communication system to the variable band filter circuit 1 and the wide band local oscillation circuit 84. At the time of transmission, the digital signal modulated by the DSP 126 is converted from a digital signal to an analog signal by the D / A converter 86, and is input to the transmission mixer circuit 83.

The transmission mixer circuit 83 is up-converted into an RF signal by the analog signal and the local oscillation signal generated by the wide-band local oscillation circuit 84, and the wide-band power amplifier (PA) 87 amplifies the RF signal to switch between transmission and reception. The circuit 81 outputs a signal via the variable low-pass filter circuit 2. The CPU 127 outputs a wireless communication system switching voltage 88 corresponding to each wireless communication system to the broadband local oscillation circuit 84.

FIG. 7 is a block diagram showing a communication device having another configuration example. In the present example, in the software defined radio apparatus shown in FIG. 6, a wide band fixed band filter 91 is used between a wide band antenna 80 and a transmission / reception switching circuit 81, and a variable low pass filter circuit 2 is A wide band power amplifier (PA) 87 is used between the high-pass filter circuits 4. In the transmission unit band variable filter 90, unnecessary signals such as harmonic signals of the transmission frequency are removed.

[0028]

The present invention has the above-described configuration, and uses a band variable filter circuit that varies a filter according to the center frequency and the bandwidth of the line communication system, thereby enabling the RF high frequency of the software defined radio to be realized. The cost can be reduced by simplifying the unit and reducing the number of parts.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a band variable filter according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram of a variable low-pass filter showing the operation principle of FIG.

FIG. 3 is a characteristic diagram of a variable high-pass filter showing the operation principle of FIG. 1;

FIG. 4 is a variable bandpass filter characteristic diagram showing the overall characteristics of FIG.

FIG. 5 is a characteristic diagram of a variable capacitance diode.

FIG. 6 is a block diagram of a software defined radio communication apparatus according to an embodiment of the present invention.

FIG. 7 is a block diagram of a software defined radio communication apparatus according to another embodiment of the present invention.

FIG. 8 is a block diagram of a conventional software defined radio communication device.

[Explanation of symbols]

1: band variable filter circuit, 2: variable low pass filter circuit, 3: wide band low noise amplifier circuit, 4: variable high pass filter circuit, 5: wide band antenna, 6: RF high frequency signal output terminal, 7: communication system switching terminal, 8-11: surface acoustic wave resonator, 12-16: variable capacitance diode, 1
7 to 23: coil, 24 to 33: capacitor, 34: transistor, 35 to 41: resistance, 42: transistor voltage application terminal, 50: low-pass filter characteristic, 60: high-pass filter characteristic, 51, 61: cut-off frequency, 52, 6
2: trap frequency, 70: overall filter characteristic, 81,
109-111: transmission / reception switching circuit, 82: reception mixer circuit, 83: transmission mixer circuit, 84: wide band local oscillation circuit, 85, 120-122: A / D converter, 86, 1
23 to 125: D / A converter, 87: Broadband power amplifier, 88: Wireless communication system switching voltage, 100: PHS
Communication system, 101: CDMA communication system, 10
2: wireless LAN communication system, 103 to 105: antenna, 106 to 108: BPF, 112 to 114: low noise amplifier, 115 to 117: power amplifier, 118: mixer circuit, 119: local oscillation circuit, 126: DSP, 12
7: CPU

Continuation of front page    F term (reference) 5J098 AA02 AA05 AA14 AA16 AB01                       AB09 AB31 AC02 AC03 AC10                       AC15 AD14 AD25 CA05 CB02                       CB06                 5K052 BB08 DD04 EE02 EE03 EE07                       FF07 FF34 GG03

Claims (6)

[Claims] 1. A variable low-pass filter circuit combining a resonator for blocking a band and a variable capacitance element, a variable high-pass filter circuit, and a wide-band amplifier disposed between the two filter circuits. Forming a signal pass band for passing only a desired signal between cutoff frequencies, and a communication system switching terminal for applying a communication system switching voltage to the variable capacitance element corresponding to a plurality of wireless communication systems; A variable band filter circuit wherein a center frequency and a bandwidth corresponding to a wireless communication system are made variable. 2. The band variable filter circuit according to claim 1, wherein a surface acoustic wave resonator is used as said resonator. 3. The band variable filter circuit according to claim 1, wherein a dielectric resonator is used as said resonator. 4. The band variable filter circuit according to claim 1, wherein an LC resonator is used as said resonator. 5. A communication device using the variable-bandwidth filter circuit according to claim 1. 6. A variable low-pass filter circuit combining a resonator for blocking a band and a variable capacitance element, a variable high-pass filter circuit, and a wide-band amplifier disposed between the two filter circuits. A variable band type having a communication system switching terminal for forming a signal pass band for passing only a desired signal between cutoff frequencies and applying a communication system switching voltage to the variable capacitance element corresponding to a plurality of wireless communication systems. A filter circuit, and a CPU for generating a communication system switching voltage corresponding to a plurality of wireless communication systems, wherein a switching voltage corresponding to the wireless communication system from the CPU is applied to a communication system switching terminal of the band variable filter circuit. A center frequency and a band of the signal pass band based on the wireless communication system switching voltage. Communication device characterized by the variable.