JPH0629947A - Correlation circuit unit for receiving spread spectrum signal - Google Patents

Abstract

PURPOSE:To provide the correlation circuit unit for receiving a spread spectrum communication(SSC) signal used simply for a demodulator employing a SAW (surface acoustic wave) convolver. CONSTITUTION:An SSC signal is fed to one terminal of a SAW convolver 4 via an amplifier 1, a BPF(band pass filter) 2, and a matching circuit 3, and an output of an oscillator 6 is modulated (7) by using a PN code and the modulated signal is fed to other terminal of the SAW convolver 4 via an amplifier 8, a BPF 9 and a matching circuit 10. The output is fetched via a matching circuit 11, amplifiers 12, 13 and a BPF 14. The amplifiers 12, 13 are controlled by a voltage from an AGC(automatic gain control) voltage IN terminal 15. The components above are assembled on one printed circuit board as a unit.

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 receiving correlation circuit unit having good characteristics, small size and easy to use.

[0002]

2. Description of the Related Art Conventionally, a so-called spread spectrum communication (SSC) device has been known as a highly confidential communication device. Spread spectrum communication transmitter (SSC transmitter)
Then, for example, digital data to be transmitted is spread (that is, spread-modulated) in a wide frequency band by using a PN (pseudo noise) code and transmitted. On the side of the spread spectrum communication receiver (SSC receiver), the PN code on the transmitter side is correlated with the received PN code in an image relationship,
Obtain a sequence of correlation peaks. Obtaining the correlation peak sequence by obtaining the correlation is usually called despread demodulation. As the correlator that takes the correlation, for example, a SAW device such as a SAW (surface acoustic wave) convolver or a matched filter can be used.

[0003]

By the way, these S
Among the AW devices, the matched filter can demodulate only one type of PN code spread spectrum signal (hereinafter referred to as SSC signal) according to its internal structure. On the other hand, the SAW convolver can demodulate the SSC signal corresponding to the externally input reference PN code,
A plurality of types of SSC signals can be demodulated by changing the reference PN code. Therefore, so-called multi-access can be performed, and multiplex communication by the SSC signal can be realized. SAW convolvers include semiconductor type and elastic type. Of these, the inventors of the present invention filed an application first (Japanese Patent Application No. 3-9
The elastic type SAW convolver has a wide dynamic range and a large BT product (B: diffusion bandwidth, T: processing time) compared to the semiconductor type.

However, the SAW convolver is an SSC
Although it is disclosed in the block diagram and the like that it can be used as a signal demodulator instead of a matched filter or the like,
No specific or detailed circuit configuration that can be operated by actually assembling is disclosed. Further, since the elastic type SAW convolver has an extremely low efficiency (-70 to -80 dBm), it cannot be operated satisfactorily only by replacing it with a matched filter or the like. Therefore, when the SSC signal is used in the field of data transmission, for example, it is almost impossible for engineers involved in data transmission to design and manufacture a demodulator using a SAW convolver.

An object of the present invention is to provide an SSC signal receiving correlation circuit unit which can be easily used as a demodulator of an SSC signal even by a person who is not familiar with communication hardware such as a person in the field of data transmission.

[0006]

In order to achieve the above object, the SSC signal receiving correlation circuit unit of the present invention comprises:
A first amplifier to which the SSC signal is input, a first bandpass filter to which the output of the first amplifier is supplied, a buffer amplifier to which a reference PN code is input, and a frequency corresponding to the carrier frequency of the SSC signal. An oscillator that oscillates, a modulator that modulates the oscillation output with a PN code output from the buffer amplifier, a second amplifier that receives the output signal of the modulator, and an output of the second amplifier. A second bandpass filter, first and second matching circuits respectively connected to output terminals of the first and second bandpass filters, and outputs of the first and second bandpass filters to the first and second matching circuits. SA supplied via the second matching circuit
W convolver, third matching circuit connected to the output terminal of the SAW convolver, automatic gain control voltage input terminal, S
A third amplifier that supplies the output of the AW convolver through the third matching circuit and amplifies the output with a gain according to the voltage supplied to the automatic gain control voltage input terminal; and The third bandpass filter supplied with the output is incorporated into one printed circuit board to form a unit.

[0007]

According to the above configuration, the SAW convolver multiplies the SSC signal input via the first amplifier, the first bandpass filter and the first matching circuit by the modulator input via the buffer amplifier. Correlation with the reference PN code that is multiplied and supplied through the second amplifier, the second bandpass filter and the second matching circuit is detected to generate its convolution output. That is, when a PN code that has an image relationship with the PN code used to create the SSC signal is input as the reference PN code, the SSC signal is despread and demodulated. The despread demodulation output is amplified by the third amplifier and then transmitted.

The matching circuit connected to the input / output circuit of the SAW convolver reduces the insertion loss of the SAW convolver. Especially when a chip-type inductor is used as the inductor of the matching circuit, a matching circuit using a toroidal coil or a variable coil with a bobbin (for example, Japanese Patent Laid-Open No. 10181718).
No.), the band can be broadened and the entire size can be reduced.
Further, by performing automatic gain control in the output amplification stage of the SAW convolver, side lobe noise caused by non-linearity of AGC in the RF or IF stage is suppressed, and reception sensitivity is improved. In addition, the unit is partially or wholly sealed with a metal package to provide a compact demodulation circuit that is resistant to disturbance.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an SSC receiving correlation circuit unit according to an embodiment of the present invention. The unit in Figure 1 is
Amplifier 1, band pass filter (BPF) 2, matching circuit 3, SAW convolver 4, buffer comparator 5,
Local oscillator 6, mixer 7, amplifier 8, BPF 9,
Matching circuits 10 and 11, amplifiers 12 and 13, and BPF1
4 is provided.

2 and 3 show examples of block configurations of an SSC transceiver to which the unit of FIG. 1 is applied. The SSC transmitter shown in FIG. 2 includes an FSK modulator (frequency shift modulator) 21, an amplifier 22, a mixer 23, a PN code generator 24, a bandpass filter (BPF) 25, and a transmission antenna 26. The FSK modulator 21 may use a direct digital synthesizer. The transmission signal is digital data created by a computer or the like, but if a microphone and an A / D converter are connected in front of the FSK modulator 21 and converted into PCM data, sound such as voice can also be transmitted.

The SSC receiver shown in FIG. 3 includes a receiving antenna 28, a BPF 29, an RF stage receiving amplifier 30, a mixer 31, a local oscillator 32, a BPF 33, an IF stage amplifier 34, a correlation circuit 35, and a correlation output buffer 36. A differential detection circuit 37, a pulse amplifier 38, and a waveform shaping circuit 39 are provided. The SSC receiver of FIG.
In contrast to the conventional SSC receiver using the matched filter, the correlation circuit unit of FIG. 1 is used instead of the matched filter. In the present embodiment, the mixers 7, 23, 31 all use balanced modulators. The delay detection circuit may be changed to a quadrature (quadrature phase) detection circuit.

Next, the operation of the SSC transceiver having the above structure will be described.

First, in the transmitter of FIG. 2, FSK (M
The modulator 21 (including SK) is serially input with digital data created by a computer or the like on the transmission side, and signals of different frequencies (f1 and f2) according to the binary signal level of each bit of the data. To generate the FSK signal. Here, the transmission rate of the digital data input to the FSK modulator 21 is, for example, 523 Kbps.
The frequency of the FSK signal is, for example, 289 MHz for f1 (“H” level) and 290 M for f2 (“L” level).
Hz.

The FSK signal output from the FSK modulator 21 is amplified by the amplifier 22 and then input to one input terminal of the mixer 23. A predetermined PN code signal is input from the PN code generator 24 to the other input terminal of the mixer 23. As a result, the FSK modulated signal is spread spectrum (SS) modulated. SS modulated signal (S
The BPF 25 attenuates unnecessary side lobe components, and the SC signal) is transmitted from the transmission antenna 26.

Next, in the receiver shown in FIG. 3, the receiving antenna 28 receives the SSC signal transmitted as described above. The received signal has side lobe noise attenuated by the BPF 29 and is input to the front end amplifier (RF stage amplifier) 30. The received signal amplified by the amplifier 30 is input to one input terminal of the mixer 31. An oscillation signal is input from the local oscillator 32 to the other input terminal of the mixer 31. The frequency of the oscillation signal from the local oscillator 32 is, for example, 41.5 MHz.
Center frequency is 289MHz (“H” level) and 290M
The RF SSC signal of Hz (“L” level) has center frequencies of 247.5 MHz and 248.5 MHz, I
F SSC signal. Such an SSC signal has side lobe noise attenuated in the BPF 33, amplified by the IF amplifier 34, and then input to the correlation circuit unit 35 shown in detail in FIG.

In the correlation circuit unit of FIG. 1, the S
The SC signal is amplified by the amplifier 1, attenuated the side lobe noise by the BPF 2, and then input to one input terminal of the SAW convolver 4, which is a correlator for performing despread demodulation, through the matching circuit 3. On the other hand, the buffer comparator 5 has a P
Enter the N code. The PN code is mixed with the output of the local oscillator 6 (for example, 247.5 MHz) by the mixer 7, and is converted into a signal having an image relationship with the SSC signal (hereinafter referred to as ISSC signal). The buffer comparator 5 is provided in order to reduce the load of the PN code supply system as a waveform shaping and a 50 ohm external buffer corresponding to the low input impedance (for example, 50Ω) of the mixer 7. The ISSC signal is amplified by the amplifier 8, the side lobe noise is attenuated by the BPF 9, and then input to the other input terminal of the SAW convolver 4 via the matching circuit 10. Matching circuit 3, 1
A spread signal passing through 0 has a wide frequency bandwidth and is
When the toroidal coil or the variable coil with bobbin as disclosed in No. 01718 is used, the insertion loss of the SAW convolver 4 cannot be sufficiently reduced due to impedance mismatch. In the present embodiment, the inductors L ₁₁ , L ₁₂ , L ₁₃ , L ₂₁ , L ₂₂ , L ₂₃ that form the matching circuits 3 and 10 are used.
By using a chip type inductor, the pass band width of the matching circuits 3 and 10 is widened and the insertion loss of the SAW convolver 4 is reduced.

The SAW convolver 4 has an SSC signal and an IS.
The correlation with the SC signal is detected and a convolution (convolution integration) output of both signals is generated. The convolution output is input to the amplifier 12 through the matching circuit 11, amplified by the amplifiers 12 and 13, and side lobe noise is attenuated by the BPF 14, and then, as a despread demodulation signal of the SSC signal, the FSK demodulation circuit of FIG. 37 is input.

Returning to FIG. 3, the despread demodulated signal is F
It is input to the SK demodulation circuit 37. This FSK demodulation circuit 3
Reference numeral 7 is a delay detection circuit using a SAW convolver similar to the SAW convolver 4 as a delay line, and delay-detects the despread demodulation signal. The detected output is amplified by the pulse amplifier 38 and waveform-shaped by the waveform shaping circuit 39 to obtain a pulse train of "0, 1" which is the same as digital data created and transmitted by a computer on the transmission side.

In FIG. 1, the amplifiers 12 and 13 are under automatic gain control (AGC). That is, the amplifiers 12 and 13
Is supplied with an AGC voltage from the AGC voltage input terminal 15, and the gain is controlled thereby. The AGC voltage may be generated, for example, according to the level of the differential detection output output from the FSK demodulation circuit 37 (FIG. 3). Figure 4 shows AGC
An example of a voltage generation circuit is shown. Although not shown, the amplifier 30 of the front end circuit shown in FIG.
Are doing. In the conventional normal AGC circuit, it has been customary to apply the AGC control signal to the front end circuit and the IF circuit. However, in the receiver using the SAW correlator, there is a problem that the side lobe noise with respect to the convolution output waveform increases and the reception sensitivity decreases due to the non-linearity of AGC, especially when the reception signal level is high. It was Therefore, an AGC control signal is applied to the amplifier 30 of the front end circuit and the amplifiers 12 and 13 of the output of the correlator that performs despread demodulation to perform automatic gain control. In this case, IF
No circuit AGC is required.

The differential detection circuit 37 may be replaced with an envelope detection circuit or a synchronous detection circuit. However, a delay detection circuit using a SAW device is preferable in order to provide a simple and low-cost detection circuit with a low bit error rate.

[0022]

As described above, according to the present invention,
It has been possible to provide an SSC signal receiving correlation circuit unit that can replace the despreading demodulator portion of the conventional SSC transmission / reception system using an element other than the SAW convolver such as a matched filter as the despreading demodulator. Therefore,
If the SSC signal receiving correlation circuit unit of the present invention is used, an SSC transmission / reception system using the SAW convolver as the despreading demodulator can be easily performed based on the knowledge of the conventional SSC transmission / reception system that does not use the SAW convolver as the despreading demodulator. It can be constructed and can be easily used as a demodulator for an SSC transmission / reception system even by people who are not familiar with the hardware of communication devices such as those in the field of data transmission. In particular, the elastic type SAW convolver has the advantages of a wide dynamic range and a large BT product, but on the other hand it is difficult for an expert to use it properly because of its large insertion loss. In addition, since these and SAW convolver were made into one unit, S
The despreading demodulator using the AW convolver could be put to practical use.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an SSC signal receiving correlation circuit unit according to an embodiment of the present invention.

2 and 3 are block diagrams of an SSC transmission / reception system using the unit of FIG.

FIG. 4 A for generating the AGC voltage in FIG.
It is a circuit diagram of a GC voltage generation circuit.

[Explanation of symbols]

1, 8, 12, 13: amplifier, 2, 9, 14: bandpass filter, 3, 10, 11: matching circuit, 4: SAW convolver, 5: buffer amplifier, 6: local oscillator,
7: mixer, 15: AGC voltage input terminal, L ₁₁ ,
L ₁₂ , L ₁₃ , L ₂₁ , L ₂₂ , L ₂₃ : Chip type inductor.

Claims (3)

[Claims] 1. A first amplifier to which an SSC signal is input,
A first bandpass filter supplied with the output of the first amplifier, a buffer amplifier input with a reference PN code, an oscillator oscillating at a frequency corresponding to the carrier frequency of the SSC signal, and the oscillation output buffered with the buffer. P output from the amplifier
Modulator that modulates with N code, second amplifier to which output signal of the modulator is input, second bandpass filter to which output of the second amplifier is supplied, first and second bandpass filters SAW convolver that supplies the outputs of the first and second matching circuits and the first and second bandpass filters connected to the output terminals of the SAW convolver and the SAW, respectively. A third matching circuit connected to the output terminal of the convolver, an automatic gain control voltage input terminal, the output of the SAW convolver is supplied through the third matching circuit, and the output is supplied to the automatic gain control voltage input terminal. A third amplifier that amplifies with a gain according to the voltage to be generated, and a third bandpass filter to which the output of the third amplifier is supplied are integrated on one printed circuit board to form a unit. Spread spectrum signal receiving correlation circuit unit, characterized in that. 2. The demodulation circuit unit according to claim 1, wherein the first and second matching circuits include chip-type inductors. 3. The demodulation circuit unit according to claim 1, wherein the third amplifier is a cascade connection of two unit amplifier stages having an automatic gain control function.