JPH098698A - Spread spectrum signal generation circuit - Google Patents

Abstract

PURPOSE: To provide the spread spectrum signal generation circuit which can be miniaturized without using a digital multiplier. CONSTITUTION: Serial transmission digital data are transformed to parallel data of a prescribed number of symbols by a shift register 1, and this parallel data has the polarity inverted in accordance with a spreading signal pattern by a polarity inverter 2 and is inputted to a waveform generation ROM 3 as address input. Primary modulation waveform obtained by subjecting transmission data to primary modulation and band limitation of one symbol section is preliminarily stored in the waveform generation ROM 3 as a digital signal, and this stored data is read out synchronously with the scan address signal from a scanner 4 with data inputted from the polarity inverter 2 as the address. It is reproduced into an analog signal by a D/A converter 5 and passes a band pass filter 6 to obtain a spread spectrum signal. In distinction from a conventional circuit, it is unnecessary to use a digital multiplier which makes the circuit scale larger.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum signal generation circuit used in a spread spectrum communication device, and more particularly to a spread spectrum signal generation circuit having a simplified structure and a reduced size.

[0002]

2. Description of the Related Art A spread spectrum communication system is used in a communication field requiring high confidentiality because it has excellent characteristics such as high confidentiality and interference resistance compared to other communication systems. It has been done. FIG. 4 shows a basic configuration example in such a spread spectrum communication system, and this configuration example will be described below with reference to the same figure.

The configuration shown in FIG. 4 has a direct diffusion (Di
1 is a configuration example of a spread spectrum communication device in a rect sequece system, the device including a multiplier 10 for multiplying a carrier by transmission digital data and modulating the carrier, and a primary modulation for removing an unnecessary signal component from a multiplication result. Filter 11
And a multiplier 12 for modulating the output signal of the primary modulation filter 11 with a spread signal (spread signal pattern).
And a bandpass filter (denoted as “BPF” in FIG. 4) 13 for removing unnecessary signals from the multiplication result.
Is provided.

A so-called primary modulated wave is obtained by the multiplier 10 and the primary modulation filter 11, and a so-called secondary modulated wave is further obtained by the multiplier 12 and the band pass filter 13.

[0005]

In such a structure,
When the multiplier 10 used for the primary modulation and the multiplier 12 used for the secondary modulation are mainly composed of digital elements, the circuit configuration tends to be relatively complicated and the power consumption tends to be relatively large. . On the other hand, when an analog type multiplier is used, a typical example thereof is a balanced modulation circuit, but it is not suitable for use as an IC and does not satisfy the demand for miniaturization of the device.

[0006] Further, as an analog type filter used as a primary modulation filter, a low pass filter for band limitation is generally used in a high order structure, and the circuit scale inevitably becomes large, and the device There was a problem that it became a factor to prevent miniaturization. Furthermore, the analog type circuit has a characteristic change due to aging compared to the digital type,
There is a problem that characteristics change easily occurs due to environmental changes, and reliability is poor.

The present invention has been made in view of the above circumstances, can be miniaturized without using a digital type multiplier having a large circuit scale, and can be aged by an aging or an environmental change which occurs in an analog circuit. It is an object of the present invention to provide a spread spectrum signal generation circuit which is stable in operation and has high reliability without fluctuations in electrical characteristics.

[0008]

A spread spectrum signal generation circuit according to the present invention comprises a data format conversion means for converting transmission data externally input in serial format into parallel data of a predetermined number of symbols, and the data. The data value of the output data output from the format conversion means is input to the polarity inversion means for changing it according to the pattern of the spread signal input from the outside, and to the address specified by the data input from the polarity inversion means. Primary modulation wave storage means in which a primary modulation wave obtained when the transmission data is subjected to primary modulation is stored in advance as a digital signal, and a digital signal output from the primary modulation wave storage means is converted into an analog signal. Digital-analog conversion means, and the digital
A band pass filter for limiting a predetermined band to the output signal of the analog converting means.

In particular, the primary modulated wave storage means performs primary modulation on the transmission data having the predetermined number of symbols at the address represented by the transmission data having the predetermined number of symbols output from the data format conversion means, and The primary modulation waveform obtained when the band limitation of one symbol section is performed is stored in advance in the digital signal format, while the transmission data having the predetermined number of symbols output from the data format conversion means is changed by the polarity inversion means. The address represented by the data obtained by the primary modulation is obtained by subjecting the data obtained by inverting the transmission data before being changed by the polarity inverting means to the primary modulation and applying the band limitation of one symbol section. It is preferable that the waveform is pre-stored in a digital signal format.

Further, the polarity reversing means has an exclusive OR circuit of a number corresponding to the number of symbols of the parallel data input from the data format converting means, and the parallel data input from the data format converting means. Each symbol is input to the corresponding exclusive OR circuit, and simultaneously, the spread signal input from the outside in serial form is also input to each exclusive OR circuit, and the logical value and spread of each symbol It is preferable that the exclusive OR with the logical value of the signal is output from each exclusive OR circuit.

[0011]

The transmission data input to the data format conversion means is converted from serial data into parallel data of a predetermined number of symbols, and the polarity reversing means changes the value of each symbol according to the spread signal pattern. While the primary modulated wave is output as an address of the primary modulated wave storage means, the primary modulated wave storage means outputs the primary modulated wave as digital data when the primary modulation of the transmission data output from the data format conversion means is performed. Is stored in advance in a storage area designated as the address data.

Since the data from the polarity reversing means input as address data to the primary modulated wave storage means changes according to the speed of the spread signal pattern, the primary modulated wave read from the primary modulated wave storage means. Is substantially equivalent to what is called secondary modulation by a spread signal, and a spread spectrum signal as an analog signal can be obtained through a digital-analog conversion means and a bandpass filter. There is.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a spread spectrum signal generating circuit according to the present invention will be described below with reference to FIGS. Here, FIG. 1 is a configuration diagram showing a configuration example in one embodiment of the spread spectrum signal generation circuit according to the present invention, and FIG. 2 is a polarity inversion used in the spread spectrum signal generation circuit shown in FIG. FIG. 3 is a circuit diagram showing an example of a circuit configuration of a power supply device, and FIG. 3 is a waveform diagram showing waveforms in a main part for explaining the operation of the spread spectrum signal generation circuit according to the present invention. The members, arrangements, and the like described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention.

As shown in FIG. 1, the spread spectrum signal generating circuit in this embodiment comprises a shift register 1 for serial-parallel converting transmission digital data, and a polarity inverter 2 for inverting the polarity of the output data of the shift register 1. A waveform generation ROM 3 that is a read-only memory in which the primary modulated wave is stored in advance; a scanner 4 that generates a scan address signal as a kind of enable signal that enables data read from the waveform generation ROM 3; A digital-to-analog converter that converts the digital signal from the generation ROM 3 into an analog signal (refer to "D /
In addition to being represented by "A", it will be hereinafter referred to as "D / A converter". ) 5 and a bandpass filter (denoted as "BPF" in FIG. 1) 6 for limiting the band of the output wave.

First, it is premised that the transmission digital data input to this circuit is input in a serial format, and the shift register 1 as the data format conversion means converts such transmission digital data into The data is sequentially shifted according to the symbol timing and is output as parallel data of K symbols. Here, K is an inter-symbol interference symbol length due to band limitation.

The polarity reversing device 2 as the polarity reversing device is for subjecting the parallel data of the K symbols input from the shift register 1 to the polarity reversing process according to the spread signal pattern. That is, when each symbol value forming the parallel data input from the shift register 1 has one of the logical values “1” or “0”, the symbol value is input according to the spread signal pattern input. The values are all inverted to the logical value "1" or "0". The spread signal is a digital signal represented by a PN sequence, which is used for so-called secondary modulation in the conventional DS system.

FIG. 2 shows a circuit example of the polarity reversing device 2. The circuit example will be described below with reference to FIG. The number of exclusive OR circuits 7 corresponding to the number K of symbols of data input from
~ ORk "). One of the input terminals of each exclusive OR circuit 7 is connected together so that the spread signal pattern is input at the same time.

On the other hand, the other input terminal of each exclusive OR circuit 7 is connected to the corresponding output terminal of the shift register 1. So, for example,
When the input data from the shift register 1 to the exclusive OR circuit 7 at a certain time point has the logical value “1” and the spread signal has the logical value “1”, the exclusive OR circuit 7 outputs When the spread signal has a logical value of "0" while the logical value of "0" is output, data of the logical value of "1", which is the input data from the shift register 1 from the exclusive OR circuit 7, is output. Is output as it is. This is exactly the same in the other exclusive OR circuits 7 as well, and the description of the individual circuits will be omitted.

Next, the waveform generation ROM 3 as the primary modulation wave storage means inputs the parallel data of K symbols whose polarities have been inverted by the polarity inverter 2 as described above as address data and inputs from the scanner 4. The data is read in synchronization with the signal.

In the waveform generation ROM 3, the primary modulation waveform obtained when the transmission digital data is subjected to the primary modulation is converted into a digital signal in a band-limited state and stored in advance. The storage address of the primary modulation waveform is such that the data of K symbols that generate the primary modulation waveform is used as the address data.

The scanner 4 divides a sampling clock input externally and generates a square wave signal of a predetermined frequency called a scan address signal which is a signal for controlling the reading of data from the waveform generation ROM 3. . The repetition period of this scan address is set to N times the carrier frequency (however, N ≧ 2).

Regarding the operation of this circuit in the above configuration,
This will be described below with reference to FIG. First, FIG. 3A shows an example of an eye pattern in one symbol section when the transmission digital data is band-limited to K symbol data. In the figure, only about 10 eye patterns are shown for easy understanding. However, in reality, the eye pattern in the case where the inter-symbol interference symbol length is K symbols and is a binary sequence, The number is
It is 2 to the Kth power.

Here, of the eye patterns shown in FIG. 3 (a), focusing on the signal a shown by the solid thick line, the signal a is a carrier wave sgn consisting of a square wave having an angular frequency ωc.
It is assumed that primary modulation is performed by [sin (ωc · t)]. However, sgn [x] is a function of the following [Equation 1].

[0024]

[Equation 1]

As a result, the modulated signal is a
.Sgn [sin (.omega.c.multidot.t)], the waveform of which is, as shown in FIG. 3 (b), the original signal a which is code-altered alternately at the carrier repetition period. In other words, it is equivalent to multiplying the signal a by a square wave signal that changes by ± 1.

In the waveform generation ROM 3, the primary modulation waveform shown in FIG. 3B is represented by K symbols obtained by passing the modulated transmission digital data through the shift register 1. This data is stored in advance as address data.

On the other hand, FIG. 3C shows the logical value "1",
Although an example of the spread signal pattern S represented by a binary sequence of “0” is shown, in the same figure, for ease of understanding,
One chip length of the spread signal is expressed as twice the carrier wave period and ¼ of one symbol length. In reality, it is appropriately set in consideration of the carrier frequency to be used and the spreading rate.

A spread signal pattern S as shown in FIG. 3C is input to the polarity inverter 2, and the K symbol data output from the shift register 1 has a polarity according to the spread signal pattern S. Upon receiving the inversion, it is output as the address data of the waveform generation ROM 3. That is, when the spread signal pattern S has the logical value "0", the K symbol data is output as it is without undergoing polarity inversion, but when the spread signal pattern S has the logical value "1". In this case, the output for each symbol is different as described above with reference to the circuit example of FIG.

The polarity of the K symbol from the shift register 1 is not inverted by the polarity inverter 2, and the waveform generation ROM 3
In the case of being input to the K symbol, the K symbol becomes the address data as it is, and the signal obtained by performing the primary modulation on the K symbol as described above with reference to FIG. 3B is read from the address.

On the other hand, when the K symbol is polarity-inverted by the polarity inverter 2, the waveform generation ROM 3 specifies the address represented by the K symbol data which is polarity-inverted by the polarity inverter 2. Become.

At the address represented by the K symbol data subjected to the polarity reversal by the polarity reversing device 2, the polarities of all K symbols are reversed and the signal waveform when the primary modulation is performed is stored in advance. This data is used for waveform generation R
It will be read from OM3.

That is, in the example of FIG. 3, the inversion of the polarities of all the K symbols corresponds to the inversion of the signal a (the bar of a) in FIG. From the ROM 3, the signal obtained when the primary modulation is applied to this signal in the manner described above is read out. In FIG. 3, a signal waveform in this case is shown in FIG.

The signal shown in FIG. 3 (d) is converted to the signal shown in FIG. 3 (b).
In the same way as in the explanation of the above, when expressed by a mathematical formula, s · a · sgn [s
in (ωc · t)]. However, s has a value defined by the function of [Formula 2] below.

[0034]

[Equation 2]

The signal thus represented is, in other words,
It can be said that the spread signal is mapped to a binary value of ± 1. Therefore, the signal read from the waveform generation ROM 3 can be regarded as equivalent to the one that is secondarily modulated by the spread signal pattern S, and this signal is converted into an analog signal by the D / A converter 5. Then, unnecessary signal components are removed by the bandpass filter 6 to obtain an analog spread spectrum signal.

As described above, in this embodiment, the primary modulation and the secondary modulation are performed without using the multiplier. Further, by using the waveform generation ROM 3, the baseband is different from the conventional one. Since the band limiting filter for the signal is unnecessary, it is possible to provide a spread spectrum signal generation circuit which can be stabilized and downsized and which is more economical than the conventional one.

In the configuration of this embodiment, the D / A converter 5
The carrier wave frequency component is included in the output signal of, but in reality, the carrier wave frequency that can be reproduced is limited depending on the conversion speed of the D / A converter used. In such a case, that is, in the case where the required carrier frequency is not compatible with the conversion speed of the D / A converter, the present invention is applied to the intermediate frequency component generation part of the transmitter. By additionally using a so-called up-converter of the frequency so as to obtain a spread spectrum signal at the finally required carrier frequency, it is possible to sufficiently cope with a higher carrier frequency.

[0038]

As described above, according to the present invention,
The primary modulated wave storing means in which the primary modulated wave is stored in advance is addressed according to the pattern change of the spread signal, so that the read primary modulated wave is substantially subjected to the secondary modulation by the spread signal. As a result, the circuit can be configured without the need for a multiplier, so that the size can be reduced, and further, the configuration can be achieved without using an analog circuit for the part that performs the primary and secondary modulation.
The present invention has an effect that it is possible to provide a highly reliable spread spectrum signal generating circuit with stable operation without causing secular change in electrical characteristics peculiar to an analog circuit.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration example in an embodiment of a spread spectrum signal generation circuit according to the present invention.

FIG. 2 is a circuit diagram showing a circuit configuration example of a polarity inverter used in the spread spectrum signal generation circuit shown in FIG.

FIG. 3 is a waveform diagram showing waveforms in a main part for explaining the operation of the spread spectrum signal generation circuit according to the present invention.

FIG. 4 is a configuration diagram showing a basic configuration example of a conventional spread spectrum communication device.

[Explanation of symbols]

1 ... Shift register, 2 ... Polarity inverter, 3 ... Waveform generation ROM, 4 ... Scanner, 5 ... D / A converter, 6
… Bandpass filters

Claims (3)

[Claims] 1. A data format conversion means for converting transmission data input in a serial format from the outside into parallel data having a predetermined number of symbols, and a data value of output data output from the data format conversion means Polarity inversion means for changing according to the pattern of the spread signal inputted from the primary polarity obtained by subjecting the transmission data input to the address specified by the data inputted from the polarity inversion means to the primary modulation. Primary modulated wave storage means in which modulated waves are stored in advance as digital signals, digital / analog conversion means for converting the digital signal output from the primary modulated wave storage means into an analog signal, and output of the digital / analog conversion means A spread spectrum signal generation circuit, comprising: a band pass filter for subjecting a signal to a predetermined band limitation. 2. The primary modulated wave storage means, for an address represented by the transmission data having a predetermined number of symbols output from the data format conversion means, performs primary modulation on the transmission data having the predetermined number of symbols, and The primary modulation waveform obtained when the band limitation of one symbol section is performed is stored in advance in the digital signal format, while the transmission data having the predetermined number of symbols output from the data format conversion means is changed by the polarity inversion means. The address represented by the data obtained by the primary modulation is obtained by subjecting the data obtained by inverting the transmission data before being changed by the polarity inverting means to the primary modulation and applying the band limitation of one symbol section. 2. The spread spectrum signal generation circuit according to claim 1, wherein the waveform is stored in advance in a digital signal format. 3. The polarity inverting means comprises exclusive OR circuits of the number corresponding to the number of symbols of the parallel data input from the data format conversion means, and the polarity inversion means converts the parallel data input from the data format conversion means. Each symbol is input to the corresponding exclusive OR circuit, and simultaneously, the spread signal input from the outside in serial form is also input to each exclusive OR circuit, and the logical value and spread of each symbol 3. The spread spectrum signal generation circuit according to claim 1, wherein the exclusive OR with the logical value of the signal is output from each exclusive OR circuit.