JPH11163829A - Spread spectrum communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spread spectrum communication equipment by suppressing output power of an undesired signal other than a transmission signal frequency band without deteriorating a reception automtically and losing a transmission signal output power to realize improvement of a communication available distance. SOLUTION: An undesired signal outputted from a power amplifier section 51 is only harmonics generated by the power amplifier section 51 by providing a band pass filter between a transmission mixer 53 and the power amplifier section 51 to suppress the undesired signal at transmission due to a leakage of a local signal and an intermediate frequency signal or the like, and the undesired signal is sufficiently suppressed even when a simple low pass filter 2 only is adopted for a filter between a transmission reception changeover circuit 3 and an antenna connection terminal 1. As a result, a loss of the transmission signal power amplified and outputted by the power amplifier section 51 to the antenna connection terminal 1 is reduced and the communication available distance is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum communication apparatus for performing transmission and reception using a spread spectrum communication system.

[0002]

2. Description of the Related Art A conventional example of a spread spectrum communication apparatus is described in, for example, Japanese Patent Application Laid-Open No. 8-163068.

FIG. 3 shows a block diagram of a conventional spread spectrum communication apparatus. In FIG. 3, reference numeral 901 denotes an antenna;
02 is a bandpass filter, 903 is a transmission / reception switching circuit, 904 is a low noise amplifier, 905 is a reception mixer, 90
6 is a local oscillator for reception, 907 is an intermediate frequency (IF)
Filter, 908 is an IF amplifier, 909 is a detection circuit, 9
10 is an RSSI circuit, 911 is an AGC circuit, 914 is a transmission local oscillator, 916 is a transmission mixer, 917 is a pre-amplifier, 918 is a power amplifier, 925 is an A / D converter, 925 is a latch circuit, and 927 is a data holding signal. , 9
28 is a D / A converter, 929 is a reference signal generation circuit, 93
0 is a comparison circuit, and 931 is a level adjustment circuit.

Hereinafter, the operation of the conventional example will be described. First, transmission will be described. Transmission data input terminal 91
5 is multiplied by the transmission local signal from the transmission local oscillator 914 in the transmission mixer 916 to be frequency-converted from an IF signal to a radio frequency transmission signal. The signal is amplified through a power amplifier 918 and transmitted and output through a transmission / reception switching circuit 903, a band-pass filter 902, and an antenna 901.

Next, the operation at the time of reception will be described. The received signal is received by an antenna 901, and after an unnecessary signal is removed by a band-pass filter 902, the signal is input to a low-noise amplifier 904 via a transmission / reception switching circuit 903. After being amplified by the low-noise amplifier 904, the signal is multiplied by the reception local signal output from the reception local oscillator 906 by the reception mixer 905 and frequency-converted into an IF signal.
The data is output from the reception data output terminal 912 via the terminal 09.

[0006]

In the above configuration, a local signal, an IF signal, and an intermodulation signal used for frequency conversion of an IF signal into a transmission signal during transmission are leaked to the output of the transmission mixer. You. When an unnecessary signal other than the frequency band of the transmission signal is output from the antenna terminal 901, when the receiver receives a signal including such an unnecessary signal, normal reception may not be possible. In addition, since it may act on radio communication equipment or electronic equipment other than the spread spectrum communication apparatus to cause malfunctions such as malfunctions, it may be out of the frequency band of such transmission signals due to regulations of the Radio Law. Must be suppressed below the specified value.

In order to deal with such a problem, in the conventional spread spectrum communication apparatus shown here, a band-pass filter 902 is inserted between the transmission / reception switching circuit 903 and the antenna 901 so that unnecessary parts other than the frequency band of the transmission signal are unnecessary. Only necessary transmission signals are output by suppressing the waves.

However, since the band-pass filter 902 has a considerable insertion loss, in this configuration, the transmission signal passes through the band-pass filter 902, and is amplified by the power amplification unit including the pre-amplifier 917 and the power amplifier 918. The transmission output power thus deteriorated. The transmission output power is an important factor related to the communication distance of the spread spectrum communication apparatus, and the transmission output power is deteriorated, so that the communicable distance is reduced.

As a means for preventing this problem, a means for preventing the deterioration of the transmission output power by increasing the gain of the power amplifying unit can be considered. However, this is a preferable method because the circuit is complicated and the problem due to an increase in current consumption is large. Absent. As another means, a means for reducing the insertion loss of the band-pass filter 902 can be considered. However, in order to reduce the insertion loss, it is necessary to sacrifice the steepness of the frequency characteristic. There is a disadvantage of deterioration. In addition, when this means is used, the input power of an unnecessary signal at the time of reception also increases at the same time, which affects the reception characteristics and deteriorates the reception characteristics.

An object of the present invention is to suppress the output power of unnecessary signals other than the transmission signal frequency band and perform communication without causing such deterioration of the reception characteristics and without losing the transmission signal output power. It is an object of the present invention to provide a spread spectrum communication device that can improve the distance.

[0011]

In a spread spectrum communication apparatus according to the present invention, a band pass filter provided between an antenna and a transmission / reception switching circuit in a conventional example is replaced with a low pass filter, and a transmission mixer and a power supply are used in a transmission circuit. A bandpass filter is provided in the middle of the amplifying unit.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to an embodiment shown in the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention. In FIG. 1, 1 is an antenna connection terminal, 2
Is a low-pass filter, 3 is a transmission / reception switching circuit, 4 is a reception circuit, 5 is a transmission circuit, 6 is a demodulation circuit, 7 is a modulation circuit,
8 is a signal processing circuit, 9 is a transmission / reception data input / output terminal, 41
Is a low-noise amplifier, 42 is a band-pass filter, 43 is a reception mixer, 44 is a local oscillator for reception, 51 is a power amplifier, 52 is a band-pass filter, 53 is a transmission mixer,
Reference numeral 54 denotes a local oscillator for transmission.

Hereinafter, the operation of the embodiment shown in FIG. 1 will be described in detail. First, the operation at the time of transmission will be described. The transmission data input from the transmission / reception data input / output terminal 9 is output to the signal processing circuit 8 by, for example, BPSK modulation, QPS
It becomes a data signal that has been subjected to narrow band modulation such as K modulation. Further, the narrow-band modulated data signal is multiplied by a digital code sequence having a frequency bandwidth wider than the data signal bandwidth called a pseudo-noise code in a modulation circuit 7 to become a spread IF modulated transmission IF signal. .

The transmission IF signal is multiplied by a transmission local signal output from a transmission local oscillator 54 in a transmission mixer 53 in the transmission circuit 5 to be converted into a transmission signal of a desired radio frequency. The transmission mixer 53 leaks and outputs unnecessary signals such as a transmission local signal, an IF signal, and an intermodulation wave in addition to the transmission signal. When these unnecessary signals are transmitted and output from the antenna connection terminal 1, an interference wave that causes deterioration of reception characteristics on the receiver side and malfunctions such as malfunctions in communication devices other than the spread spectrum communication device or other electronic devices. Since the output signal of the transmission mixer 53 is passed through the band-pass filter 52 before being amplified by the power amplifier 51, unnecessary signals other than the frequency band of the desired transmission signal are suppressed. .

The transmission signal from which the unnecessary signal has been removed is amplified in the transmission output level by the power amplifying section 51 and transmitted and output through the transmission / reception switching circuit 3, the low-pass filter 2, and the antenna connection terminal 1.

Hereinafter, the reason why the band-pass filter 52 is provided between the transmission mixer 53 and the power amplifier 51 will be described.
In the configuration in which the band-pass filter is provided after the power amplifying unit 51, the power amplifying unit 51 has no frequency selectivity.
Not only the transmission signal but also a signal of an unnecessary frequency component other than the frequency band of the transmission signal leaked and output from the transmission mixer 53 is amplified. As a result, if the band-pass filter is located downstream of the power amplifying unit 51, such unnecessary signals cannot be sufficiently suppressed, and the unnecessary signals amplified by the power amplifying unit 51 are connected to the antenna connection as interference waves. It is conceivable that the signal is transmitted via the terminal 1. In addition, since the transmission signal power amplified by the power amplification unit 51 is lost due to the insertion loss of the bandpass filter, it is not desirable to provide the bandpass filter after the power amplification unit 51. As a countermeasure, it is conceivable to increase the gain of the power amplifying unit 51 so that a band-pass filter having a steep characteristic is installed at the subsequent stage of the power amplifying unit 51 to suppress unnecessary signals and maintain the transmission signal power. However, in order to increase the gain of the power amplifying unit 51, it is also necessary to set the output power of the power amplifying unit 51 higher, which is not preferable because the circuit becomes complicated and the current consumption increases. On the other hand, the band-pass filter 52 is connected to the transmission mixer 53 and the power amplifier 5.
By installing the signal in the middle of 1, unnecessary signals such as a transmission local signal, an IF signal, and an intermodulation wave leaked and output from the transmission mixer 53 can be easily suppressed before being amplified by the power amplifier 51. In addition, unnecessary signals can be prevented from being output from the antenna connection terminal 1. For the above reason, the band-pass filter 52 is connected to the power amplifying section 51.
Installed in front of

However, it is necessary to newly provide a means for suppressing an unnecessary signal generated in the power amplifying section 51 by providing a filter before the power amplifying section 51. As unnecessary signals that may be generated in the subsequent stage of the band-pass filter 52, harmonics such as a second harmonic and a third harmonic generated in the power amplifying unit 51 can be considered, and the low-pass filter 2 is used as a means for suppressing these harmonics. It is installed after the transmission / reception switching circuit 3. Since these harmonics have a higher frequency than the frequency band of the transmission signal, the low-pass filter 2 can be suppressed without requiring a steep characteristic. Therefore, the low-pass filter 2 can suppress these harmonics with a simple configuration. In addition, since steep characteristics are not required, the insertion loss can be reduced, and the transmission signal can be supplied to the antenna connection terminal 1 from the output power of the power amplification unit 51 with almost no deterioration.

Next, the operation at the time of reception will be described. The filter at the subsequent stage of the antenna connection terminal 1 is a low-pass filter 2
By doing so, the insertion loss is reduced as compared with the band-pass filter shown in the conventional example, and as a result, the noise figure at the time of reception is reduced and the reception characteristics can be improved.
Conversely, by using a low-pass filter, an unnecessary wave lower than the frequency band of the received signal is input to the spread spectrum communication apparatus. As described in the operation at the time of transmission, the filter provided in this portion is It is necessary to reduce the insertion loss in order to prevent the loss of the transmission signal output power, and it is impossible to configure a filter having a large suppression degree and a sharp characteristic on the antenna connection terminal 1 side from the transmission / reception switching circuit 3 in the first place. For a stable reception operation, a steep filter having a large suppression degree for removing unnecessary signals other than the reception signal frequency band is required in the reception circuit 4 subsequent to the transmission / reception switching circuit 3. Even if a signal whose frequency is not required is input, the reception characteristics are not affected.

The received signal input to the receiving circuit 4 is amplified by the low noise amplifier 41, the unnecessary signal is suppressed by the band-pass filter 42, and the receiving local oscillator 44 is received by the receiving mixer 43.
After being frequency-converted into a reception intermediate frequency by multiplying the reception local signal output from the reception local signal, the signal is output to the demodulation circuit 6 as a reception IF signal. The demodulation circuit demodulates the spread-spectrum modulation by despreading the received IF signal that has been spread. Further, in the signal processing circuit 8, the narrow band modulation such as BPSK and QPSK described in the description at the time of transmission is demodulated and output from the transmission / reception data input / output terminal 9 as reception data.

As described above, according to the present embodiment, at the time of reception, unnecessary signals other than the frequency band of the desired received signal are suppressed by the low-pass filter 2 in the high-frequency band. Since unnecessary signals are suppressed by a filter having a large suppression degree and a steep characteristic in the circuit 4, only the frequency band of the received signal is input to the demodulation circuit, and good demodulation characteristics are realized.

At the time of transmission, a band-pass filter 52 is provided between the transmission mixer 53 and the power amplifying unit 51, so that a signal which becomes an interference wave when transmitted from an antenna such as a transmission local signal and an IF signal is transmitted to the power amplifying unit. It is suppressed at the stage before 51. As a result, the transmission local signal, the IF signal, and the like leaked from the transmission mixer are not amplified by the power amplification unit 51, and only the second harmonic, the third harmonic, and the like generated by the power amplification unit 51 are output from the antenna. This is an unnecessary signal that may be generated. However, these harmonics can be suppressed by providing the low-pass filter 2 having a simple configuration.

As a result, it is possible to reduce the loss of the transmission signal output from the power amplification unit 51 in the filter at the subsequent stage of the power amplification unit 51, and to output the transmission output power at a power substantially equal to the output power of the power amplification unit 51. Is possible, and the communicable distance of the spread spectrum communication apparatus can be extended.

As for the operation at the time of reception, by using the low-pass filter 2 between the antenna connection terminal 1 and the transmission / reception switching circuit 3, the noise figure can be suppressed and good demodulation characteristics can be obtained.

FIG. 2 is a block diagram showing a second embodiment of the present invention. Reference numeral 55 denotes a local oscillator. The same reference numerals are given to the same functional blocks as those in FIG. 1, and the description of the operation is omitted.

Hereinafter, the operation of this embodiment will be described in detail. In the embodiment shown in FIG. 1, if the frequency of the transmission IF signal output from the modulation circuit 7 is the same as the frequency of the reception IF signal input to the demodulation circuit 6, the transmission local oscillator 54 shown in FIG. The function of the local oscillator 44 for reception can be the same as that of the local oscillator for reception, and the function can be substituted by one local oscillator 55. In this case, the local signal output from the local oscillator 55 is supplied to the transmission mixer 53 at the time of transmission to convert the transmission intermediate frequency signal into a radio frequency signal, and supplied to the reception mixer 43 at the time of reception. To a received intermediate frequency signal. Other functions are the same as those of the embodiment shown in FIG.

As described above, according to this embodiment,
With only one local oscillator, a spread spectrum communication apparatus can be realized with a simpler configuration.

[0028]

As described above, a band-pass filter is provided between the transmission mixer and the power amplifier in the transmission circuit as in the present invention, so that signals unnecessary for transmission are not input to the power amplifier. By doing so, the filter provided downstream of the power amplifying unit 51 can reduce the insertion loss by using only the low-pass filter 2 having a simple configuration. As a result, the loss of transmission output power is reduced, and the communicable distance of the spread spectrum communication apparatus can be extended.

[Brief description of the drawings]

FIG. 1 shows a first example of a spread spectrum communication apparatus according to the present invention.
It is a block diagram showing an example.

FIG. 2 shows a second embodiment of the spread spectrum communication apparatus according to the present invention.
It is a block diagram showing an example.

FIG. 3 is a block diagram showing a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Antenna connection terminal, 2 ... Low-pass filter, 3 ... Transmission / reception switching circuit, 4 ... Receiving circuit,
41 low noise amplifier, 42 bandpass filter, 43 reception mixer, 44 local oscillator for reception, 5 transmission circuit, 51 power amplifier, 52
... Band pass filter, 53 ... Transmission mixer, 5
4 Local oscillator for transmission 55 Local oscillator 6 Demodulation circuit 7 Modulation circuit 8
Signal processing circuit, 9 ... transmission / reception data input / output terminal, 90
1 ... antenna, 902 ... bandpass filter,
903: transmission / reception switching circuit, 904: low noise amplifier, 905: reception mixer, 909: detection circuit, 918: power amplifier, 917: preamplifier, 916: transmission mixer , 906: Local oscillator for reception, 914: Local oscillator for transmission.

Claims (5)

[Claims] An antenna connection terminal, a transmission circuit, a reception circuit, a modulation circuit for performing spread spectrum modulation, a demodulation circuit for despreading and demodulating spread spectrum modulation, the modulation circuit and the demodulation circuit and spectrum A signal processing circuit for connecting to a data signal input / output to / from a spread communication apparatus, wherein the transmission circuit frequency-converts the transmission intermediate frequency signal output from the modulation circuit to a radio frequency. Frequency converting means, first suppressing means for selectively suppressing a signal in accordance with the frequency of an input signal, and power amplifying means, wherein the receiving circuit is configured to receive the radio signal inputted from an antenna through an antenna connection terminal. Spread-spectrum communication having second frequency conversion means for frequency-converting a received signal of a frequency into a received intermediate frequency signal suitable for the operation of the demodulation circuit. In the transmitting device, the first suppressing means is provided between the frequency converting means and the power amplifying means in the transmitting circuit, and between the antenna connection terminal and the receiving circuit, according to a frequency of a signal inputted. Second to selectively suppress the signal
A spread-spectrum communication device comprising a suppression unit. 2. The spread spectrum communication apparatus according to claim 1, wherein the first suppression means provided in the transmission circuit is constituted by a band-pass filter, and is provided between the antenna connection terminal and the reception circuit. The spread spectrum communication apparatus according to claim 2, wherein said second suppressing means is constituted by a low-pass filter. 3. The spread spectrum communication apparatus according to claim 2, wherein said first frequency conversion means of said transmission circuit transmits a transmission local signal output by a transmission local oscillation circuit to a transmission intermediate signal output by said modulation circuit. Multiplying the frequency signal to obtain a transmission signal that is a radio frequency, wherein the second frequency conversion means of the reception circuit converts the reception local signal output from the reception local oscillation circuit through the antenna connection terminal. A spread-spectrum communication apparatus, which obtains a reception intermediate frequency signal to be output to a demodulation circuit by multiplying an input radio frequency reception signal. 4. The spread spectrum communication apparatus according to claim 2, wherein the first frequency conversion means of the transmission circuit multiplies a local signal output from a local oscillation circuit by a transmission intermediate frequency signal output from the modulation circuit. The second frequency converting means of the receiving circuit receives a local signal output from the local oscillation circuit and receives a radio signal input through the antenna connection terminal. A spread spectrum communication apparatus for obtaining a received intermediate frequency signal to be output to a demodulation circuit by multiplying a signal. 5. The spread spectrum communication apparatus according to claim 2, further comprising a transmission / reception switching circuit, wherein the transmission / reception switching circuit is configured to transmit the transmission circuit and the low-pass filter when the spread spectrum communication apparatus transmits. And a transmission / reception switching function for connecting the low-pass filter and the receiving circuit at the time of reception.