JPH10303858A - Spread spectrum communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spread spectrum communication equipment where no deterioration in a reception characteristic is caused, a transmission signal output level is not lost and improvement of a communication available range is realized. SOLUTION: Only an LPF 2 is provided between a transmission reception changeover switch 3 and an antenna connection terminal 1, an HPF 41 is provided between the switch 3 and a low noise amplifier 42, and an undesired wave with a high frequency is eliminated by the LPF 2 and an undesired wave with a low frequency is eliminated at the HPF 41 at the reception. A BPF 53 is provided between a transmission mixer 54 and a pre-stage amplifier 52 at transmission, then undesired waves from a power amplifier 51 are only harmonics, which are eliminated by the LPF 2. As a result, an output is obtained from an antenna connection terminal 1 without losing the transmission signal level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a 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 switch, 904 is a low noise amplifier, 905 is a reception mixer,
906 is a local oscillator, 907 is an IF filter, 90
8 is an IF amplifier, 909 is a detection circuit, 910 is RSSI
Circuit, 911 is an AGC circuit, 914 is a carrier oscillator,
916 is a modulation mixer, 917 is a pre-stage amplifier, 918 is a power amplifier, 925 is an A / D converter, 926 is a latch circuit, 927 is a data hold signal, 928 is a D / A converter,
929 is a reference signal generation circuit, 930 is a comparison circuit, 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
The spread spectrum signal input to 5 is converted into a radio frequency by the carrier signal from the carrier oscillator 914 and the transmission mixer 916, amplified by the pre-stage amplifier 917 and the transmission power amplifier 918, and transmitted / received by the switch 903 and the band pass filter 902. , Antenna 901
Is transmitted and output.

Next, the operation at the time of reception will be described. The received signal is received by an antenna 901, an unnecessary signal is removed by a band-pass filter 902, and then input to a low-noise amplifier 904 via a transmission / reception switch 903. After being amplified by the low noise amplifier 904, the frequency is converted into an IF signal by the reception mixer 905 and the local oscillator 906, and the data is output from the reception data output terminal 912 via the detection circuit 909.

[0006]

At the time of reception, signals of all frequencies are input to the antenna terminal 901. However, if a signal with a frequency other than the desired received signal is input to the detection circuit 909, the error rate of the demodulated data increases and the normal reception state cannot be maintained.
Unwanted signals other than the desired frequency band that cause such deterioration of the demodulation characteristics must be sufficiently suppressed before the received signal reaches the demodulation circuit.

Further, even during transmission, 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 is performed. May be impossible, and may act on wireless communication equipment or electronic equipment other than the spread spectrum communication equipment and cause interference such as malfunctions. Signals other than the frequency band of the transmission signal must be suppressed below a specified value.

In order to deal with such a problem, in the conventional spread spectrum communication apparatus shown here, a bandpass filter 902 is inserted between the transmission / reception switching circuit 903 and the antenna 901, so that an unnecessary signal at the time of reception is eliminated. Suppression and interference waves during transmission are suppressed.

However, since the bandpass filter 902 has a considerable amount of insertion loss, the transmission signal passing through this bandpass filter 902 during transmission deteriorates the transmission output level amplified by the pre-stage amplifier 909 and the power amplifier 908. Resulting in. The transmission output level is an important factor that affects the communication distance of the spread spectrum communication device, and the communicable distance is deteriorated by the deterioration of the transmission output level. It is conceivable to increase the output level of the power amplifier in order to increase the transmission output level. However, this is not a preferable method because the circuit is complicated and the problem due to the increase in current consumption is large.

When the insertion loss of the bandpass filter 902 is reduced, the steepness of the frequency characteristic must be sacrificed, so that the degree of suppression of unnecessary waves is deteriorated. Even if a bandpass filter that suppresses the suppression of unnecessary waves is used to suppress the insertion loss, the input level of the unnecessary signal at the time of reception becomes large, and the reception characteristics deteriorate.

An object of the present invention is to provide a spread spectrum communication apparatus which can improve the communicable distance without causing such deterioration of the reception characteristics and without losing the transmission signal output level. .

[0012]

According to a spread spectrum communication apparatus of the present invention, a band pass filter provided between an antenna and a transmission / reception switch in a conventional example is replaced with a low pass filter, and a transmission / reception switch is provided in a receiving circuit. A low-pass amplifier and a high-pass filter, and a transmission circuit is provided with a band-pass filter after the transmission mixer.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the embodiments shown in the drawings.

FIG. 1 is a block diagram showing an 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 switch, 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 high-pass filter, 42 is a low-noise amplifier, 43 is a band-pass filter, 44 is a reception mixer, 45 is a local oscillator for reception, 51 is a power amplifier, 52 is a pre-amplifier, 5
3 is a band-pass filter, 54 is a transmission mixer, and 55 is a local oscillator for transmission.

The operation of the embodiment shown in FIG. 1 will be described in detail below. 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 subjected to, for example, BPSK modulation, QPS in the signal processing circuit 8.
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 generate a spread-spectrum-modulated transmission intermediate frequency signal. Become.

The transmission intermediate frequency signal is multiplied by the transmission local signal output from the transmission local oscillator 55 in the transmission mixer 54 in the transmission circuit 5 and frequency-converted into a transmission signal of a desired radio frequency. In addition to this transmission signal, a transmission local signal and a signal such as an intermediate frequency signal are leaked from the transmission mixer 54, and when these are transmitted and output from the antenna connection terminal 1, communication devices other than the present spread spectrum communication device or other The output signal of the transmission mixer 54 may be a band-pass filter 5
3, unnecessary frequency components other than the desired radio frequency transmission signal are suppressed.

Further, the transmission signal has its transmission output level increased by the pre-amplifier 52 and the power amplifier 51 in the transmission circuit 5, and the transmission / reception switch 3, the low-pass filter 2,
The signal is transmitted and output from an antenna (not shown) via the antenna connection terminal 1.

Here, in the configuration in which the bandpass filter 53 is provided in the subsequent stage of the pre-stage amplifier 52, the pre-stage amplifier 52 does not have frequency selectivity, so that it is amplified including a signal of an originally unnecessary frequency component. As a result, sufficient suppression may not be obtained by the bandpass filter 53, and the interference wave amplified by the pre-stage amplifier 52 may leak directly to the antenna connection terminal 1 and be transmitted. In addition, since the gain obtained by the pre-amplifier 52 is lost due to the passing loss of the band-pass filter 53, it is not desirable to provide the band-pass filter 53 after the pre-amplifier 52. By increasing the gains of the pre-amplifier 52 and the power amplifier 51, it is conceivable to install the band-pass filter 53 after the pre-amplifier 52. However, increasing the gains of the pre-amplifier 52 and the power amplifier 51 requires an output level. Is also set higher, which increases circuit complexity,
It is not preferable because it increases current consumption. For the above reason, the bandpass filter 53 is not installed even after the power amplifier 51.

Unwanted waves that may be generated in the subsequent stage of the bandpass filter 53 are the pre-stage amplifier 52 and the power amplifier 5.
Although harmonics such as a second harmonic, a third harmonic, and the like that may occur in 1 are conceivable, these harmonics are suppressed by the low-pass filter 2. Since these harmonics have a higher frequency than the desired radio frequency, the low-pass filter 2 does not require steep characteristics, so a simple configuration is sufficient. As a result,
The insertion loss is also reduced, and the transmission signal is supplied from the output level of the power amplifier 51 to the antenna connection terminal with almost no deterioration.

Next, the operation at the time of reception will be described. Since the received signal input from the antenna has various frequency components, the low-pass filter 2 in the latter stage of the antenna connection terminal 1 removes unnecessary high-frequency waves, and further passes through the transmission / reception changeover switch 3 to the receiving circuit 4. The high-pass filter 41, which is input, removes unnecessary waves in the low frequency range of the desired radio frequency signal. The received signal from which unnecessary high and low frequency waves have been removed is input to the low noise amplifier 42.

As described in the operation of the transmitting section, the low-pass filter 2 has a simple structure and reduces the insertion loss, so that the noise characteristic of the receiving section of the present spread spectrum communication apparatus is good. Undesired waves included in the received signal are mostly in the low band rather than the high band. Therefore, the characteristics of the high-pass filter 41 need to be steep, but it is not necessary to suppress high frequencies, so that the insertion loss can be reduced as compared with the case where the band-pass filter is used. In this embodiment, it is assumed that unnecessary waves in the vicinity of a desired radio frequency are not sufficiently suppressed, and a band-pass filter 43 having a steep characteristic is provided downstream of the low noise amplifier 42 in order to improve demodulation characteristics. Has been arranged. Since the band-pass filter 43 is provided at a stage subsequent to the low-noise amplifier 42, it has little effect on deterioration of noise characteristics. The insertion loss is equal to that of the low noise amplifier 42.
Can be dealt with by increasing the gain. Increasing the gain of the low-noise amplifier 42 is equivalent to the pre-amplifier 52,
This can be easily realized as compared with an increase in the gain of the power amplifier 51.

The reception signal output from the band-pass filter 43 is multiplied by the reception local signal output from the reception local oscillator 45 by the reception mixer 44, frequency-converted to an intermediate frequency, and output to the demodulation circuit 6 as a reception intermediate frequency signal. Is done. In the demodulation circuit, the spread spectrum modulation is demodulated by despreading the spread spectrum received intermediate frequency signal. 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 this embodiment, unnecessary waves included in the received signal at the time of reception are removed by removing low-frequency unnecessary waves with the low-pass filter 2 and removing high-frequency unnecessary waves with the high-pass filter 41. By removing unnecessary waves in the band, good demodulation characteristics can be realized without inputting unnecessary waves to the demodulation circuit.

At the time of transmission, a band-pass filter 53 is provided at the subsequent stage of the transmission mixer 54 so that a signal which becomes an interference wave when transmitted from an antenna such as a transmission local signal and an intermediate frequency signal can be transmitted to the preamplifier 52 and the power amplifier. It is suppressed at the stage before 51. As a result, only the higher harmonics such as the second harmonic wave, the third harmonic wave, etc. which can be generated in the amplifier can be the interference waves generated in the latter stage of the front stage amplifier 52 and the power amplifier 51. Suppression can be achieved by using only the low-pass filter 2 having a simple configuration as the filter after the power amplifier 51.

As a result, the pre-stage amplifier 52 and the power amplifier 5
It is possible to reduce the loss of the transmission signal output from the filter 1 by the filter, and to output the transmission output level at a level substantially equal to the output level of the power amplifier 51, thereby extending the communicable distance of the spread spectrum communication apparatus. It becomes possible.

FIG. 2 is a block diagram showing a second embodiment of the present invention, in which 46 is 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 intermediate frequency signal output from the modulation circuit 7 and the frequency of the reception intermediate frequency signal input to the demodulation circuit 6 are the same frequency, the transmission local frequency in FIG. The functions of the oscillator 45 and the receiving local oscillator 55 can be the same,
The function can be performed by one local oscillator 46. In this case, the local signal output from the local oscillator 46 is supplied to the transmission mixer 54 at the time of transmission to convert the transmission intermediate frequency signal into a radio frequency signal, and supplied to the reception mixer 44 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,
Only one local oscillator is needed, and it becomes possible to realize a spread spectrum communication device with a simpler configuration.

[0029]

As described above, according to the present invention, in the operation at the time of transmission, the filter provided downstream of the power amplifier 51 can reduce the insertion loss by using only the low-pass filter 2 having a simple configuration. As a result, the transmission output level increases, and the communicable distance of the spread spectrum communication apparatus can be extended. In addition, by providing the high-pass filter 41 in addition to the low-pass filter 2 at the time of reception, it is possible to remove a signal unnecessary for demodulation, and to maintain good demodulation characteristics.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a spread spectrum communication apparatus according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a spread spectrum communication device according to the present invention.

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

[Explanation of symbols]

1 ... Antenna connection terminal 2 ... Low pass filter 3 ... Transmission / reception changeover switch 4 ... Reception circuit 41 ... High pass filter 42 ... Low noise amplification circuit 43 ... Band pass filter 44 ... · Receiving mixer 45 ··· Receiving local oscillator 5 ··· Transmission circuit 51 ··· Power amplifier 52 ··· Pre-amplifier 53 ··· Bandpass filter 54 ··· Transmission mixer 55 ··· 6 demodulation circuit 7 modulation circuit 8 signal processing circuit 9 transmission / reception data input / output terminal 901 antenna 902 bandpass filter 903 transmission / reception switch 904・
Low-noise amplifier 905 reception mixer 909 detection circuit 918 power amplifier 917 pre-amplifier 916 transmission mixer 906 reception local oscillator 914 carrier oscillator

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuhide Tamizu 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture

Claims (5)

[Claims] 1. A spread spectrum communication device, comprising at least an antenna terminal, a transmission circuit, a reception circuit, a modulation circuit for performing spread spectrum modulation, and a demodulation circuit for despreading and demodulating spread spectrum modulation. Data transmission / reception to / from the spread spectrum communication device, a signal processing circuit for connecting the modulation circuit and the demodulation circuit, and the transmission circuit is at least a spread spectrum transmission intermediate signal output from the modulation circuit. A receiving intermediate frequency signal suitable for the operation of the demodulation circuit, the receiving circuit including at least a means for converting a frequency signal into a radio frequency, and a power amplifying means. In the spread spectrum communication device having means for frequency conversion according to the above, according to the frequency of the signal input to the transmission circuit, Means for selectively suppressing the signal are provided, and means for selectively suppressing the signal according to the frequency of the input signal is provided between the antenna terminal and the receiving circuit, and the signal is input to the receiving circuit. A spread spectrum communication device, comprising means for selectively suppressing a signal in accordance with the frequency of the signal. 2. The spread spectrum communication device according to claim 1, wherein the means for selectively suppressing the signal according to the frequency of the input signal, which is provided in the transmission circuit, is configured by a bandpass filter, The means for selectively suppressing the signal according to the frequency of the input signal, which is provided between the antenna terminal and the receiving circuit, is composed of a low-pass filter, and has a frequency of the input signal provided in the receiving circuit. A spread spectrum communication apparatus, wherein the means for selectively suppressing a signal in response to the signal is a high-pass filter. 3. The spread spectrum communication device according to claim 2, wherein the frequency conversion means of the transmission circuit outputs the transmission local signal output from the transmission local oscillator circuit to the transmission intermediate frequency signal output from the modulation circuit. To obtain a transmission signal of a radio frequency, and the frequency conversion means of the reception circuit, the reception local signal output from the reception local oscillator circuit, the reception signal of the radio frequency input from the transmission / reception changeover switch. A spread spectrum communication device, characterized in that a received intermediate frequency signal output to a demodulation circuit is obtained by multiplying by. 4. The spread spectrum communication apparatus according to claim 2, wherein the frequency conversion means of the transmission circuit multiplies a transmission intermediate frequency signal output by the modulation circuit by a local signal output by a local oscillation circuit. A transmission signal that is a radio frequency is obtained, and the frequency conversion means of the reception circuit demodulates the radio signal by multiplying the local signal output from the local oscillation circuit by a radio frequency reception signal input from the transmission / reception switch. A spread spectrum communication device characterized in that it receives a reception intermediate frequency signal to be output to a circuit. 5. The spread spectrum communication device according to claim 1, further comprising a transmission / reception changeover switch, wherein the transmission / reception changeover switch includes the transmission circuit and the low-pass when the spread spectrum communication device is transmitting. A spread spectrum communication device having a transmission / reception switching function for connecting a filter and connecting the low-pass filter and the receiving circuit during reception.