JPH0795128A - Spread spectrum communication receiver - Google Patents

Abstract

(57) [Summary] [Purpose] To reduce the power consumption and size of a spread spectrum communication receiver. A secondary demodulation signal obtained by despreading and demodulating a received spread spectrum signal is primary demodulated by a quad ratcher demodulation circuit including a 90 ° phase shifter 51, a mixer 52 and a low pass filter 53.

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 receiver with reduced power consumption and reduced size.

[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, first the digital data to be transmitted is FSK.
After performing primary modulation such as modulation, a PN (pseudo noise) code is used to spread (that is, spread-modulate) in a wide frequency band and transmitted. This spread modulation is also called secondary modulation.

On the side of the spread spectrum communication receiver (SSC receiver), the correlation between the PN code on the transmitter side and the received PN code in an image relationship is obtained to obtain a series of correlation peaks. Obtaining the correlation peak sequence by taking the correlation is called secondary demodulation or 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. Next, the correlation peak string is detected, the waveform is shaped, and demodulated. Detecting the correlation peak train is called primary demodulation. Known detection methods for primary demodulation include, for example, an envelope detection method, a synchronous detection method, and a delay detection method.

Among these detection methods, the envelope detection method has a low detection efficiency and a large bit error rate, and the synchronous detection method has a complicated circuit structure and high cost. The differential detection method used was mainly used.

That is, in the past, S was used as a secondary demodulation circuit.
A despreading circuit using an AW convolver and a differential detection circuit using a SAW delay line as a primary demodulation circuit have been generally adopted.

[0006]

However, SAW
The output level of the secondary demodulation circuit using the convolver is a weak level, and the delay detection circuit using the SAW delay line has a large insertion loss in the SAW delay line. Therefore, as shown in FIG. High frequency amplifier (RF.AM
P) 64-66 are required. As a result, the power consumption is increased and the mounting area (the area of the printed wiring board) is increased, which hinders the low power consumption and the downsizing of the SSC receiver and the SSC communication device using the SSC receiver. . In FIG. 4, 61 is a two-way divider, 62
Is a SAW delay line, 63 is a mixer (double balanced modulator), 6
7 is a filter.

The present invention has been made in view of the above problems in the conventional example, and an object thereof is to reduce the power consumption and the size of a receiver for spread spectrum communication.

[0008]

In order to achieve the above object, a spread spectrum communication receiver according to the present invention has a secondary demodulation signal obtained by despread demodulating a received spread spectrum signal and then a primary demodulation signal. A quadratcher demodulation circuit (quadrature phase detection circuit) is used as a circuit for doing so.

In the preferred embodiment of the present invention, a surface acoustic wave convolver is used as a correlator for despreading and demodulating a received signal.

[0010]

The quad ratcher demodulation circuit uses a 90 ° phase shifter instead of the delay line. A commercially available wide band 90 ° phase shifter having a band of 100 MHz or more can be used as the 90 ° phase shifter. However, since such a phase shifter has a small insertion loss, a high frequency amplifier is provided especially in the primary demodulation circuit. No need. Also, the shape of the phase shifter itself is relatively small. Therefore, the spread spectrum communication receiver can be configured to have a small size and low power consumption.

[0011]

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

FIG. 1 is a block circuit diagram of an SSC receiver according to an embodiment of the present invention. The SSC receiver shown in the figure receives a spread spectrum (SS) signal in the 2.4 GHz band, and includes a receiving antenna 21, a first receiving amplifier 22 in the RF stage, a bandpass filter (BPF) 23, and a second receiving amplifier 21.
A reception amplifier 24, a mixer (double balanced modulator) 25, a local oscillator 26, an IF stage amplifier 27, a BPF 28, a SAW device convolver 30, which is a correlator, a buffer amplifier 31, a local oscillator 32, a mixer 33, an attenuator ( ATT) 34, BPF 35, correlator output amplifier 3
6, a BPF 37, and a primary demodulation circuit 50 including a quadratcher demodulation circuit that is a feature of the present invention.

Next, the operation of the receiver thus configured will be described. Here, a case will be described in which a primary modulation signal obtained by PCMizing an acoustic signal is FSK-modulated, and a transmission signal obtained by SS spread modulation is received and reproduced.

In this receiver, the receiving antenna 21 receives a signal transmitted from a transmitter (not shown). The reception signal is amplified by the first reception amplifier 22 at the front end, then the side lobe noise is removed by the BPF 23, and is input to the second reception amplifier 24. The reception signal amplified by the amplifier 24 is input to one input terminal of the mixer 25. A 2.2 GHz band oscillation signal is input from the local oscillator 26 to the other input terminal of the mixer 25. Thereby, the received signal in the 2.4 GHz band is frequency-converted into the intermediate frequency (IF) signal in the 200 MHz band. By adopting a PLL synthesizer oscillation circuit as the local oscillator 26, the frequency of the oscillation signal can be switched to appropriately select the center frequency of the reception signal.

The IF signal is amplified by the amplifier 27 in the IF stage, and is input to one input terminal of the SAW convolver 30 which is a correlator for performing secondary demodulation (SS spread demodulation) via the BPF 28. The SS reference signal is input to the other input terminal of the SAW convolver 30. The SS reference signal is transmitted from the PN code generator (not shown) at the TTL level and is input via the buffer amplifier 31.
The PN code having an image relationship with the N code and the 200 MHz band oscillation signal output from the local oscillator 32 are mixed by the mixer 33 and are obtained through the ATT 34 and the BPF 35.

The SAW convolver 30 has a function as a BPF in addition to a function as a correlator, and detects the correlation between the received signal and the PN code to generate a convolution output. This convolution output is SAW
It is amplified by the output amplifier 36 of the convolver 30, and the BPF3
It is input to the primary demodulation circuit 50 via 7.

FIG. 2 shows a more detailed structure of the primary demodulation circuit in FIG. In FIG. 2, 51 is a 90 ° phase shifter,
Reference numeral 52 is a mixer, and 53 is a low-pass filter (LPF). The convolution output secondarily demodulated by the SAW convolver 30 shown in FIG.
Enter 1. The phase shifter 51 divides the convolution output into two and outputs the phase of one output Q (90 °) by shifting the phase of the other output I (0 °) by 90 °. The two signals output from the phase shifter 51 and having phases different from each other by 90 ° are input to the two input terminals of the mixer 52, respectively. The mixer 52 mixes these input signals. The mixing output is output via the LPF 53. As a result, the primary demodulation (quad ratcher detection) of the convolution output is performed.

Since this primary demodulation circuit can use a 90 ° phase shifter having an insertion loss smaller than that of the SAW delay line, it is not necessary to use an amplifier for high frequency amplification in the demodulation circuit. Therefore, the SSC receiver and the S using the SSC receiver
The power consumption and shape of the S communication device can be reduced.

A signal OUT obtained by demodulating the convolution output by the primary demodulation circuit 50 is amplified by a pulse amplifier in a reproduction circuit (not shown), waveform-shaped by a waveform-shaping circuit, and converted into analog data by a D / A converter. ,
Sound is output from the speaker through the low frequency amplifier and the LPF. FIG. 3 is a detailed circuit diagram of the pulse amplifier 55 that amplifies the signal OUT of FIG. The pulse amplifier 55 is a DC amplifier having a differential amplifier in the first stage for amplifying the signal OUT of the minute level signal.

Returning to FIG. 1, the amplifier 24, I of the RF circuit
Amplifier 27 of F circuit, amplifier 3 of the latter stage of convolver 30
6 and the SS reference signal input level to the convolver 30 is automatically gain controlled (AGC). The AGC control signal may be generated according to the level of the acoustic signal output from the D / A converter of the reproduction circuit, for example.

[0021]

As described above, according to the present invention,
Since the quadrature detection circuit is used to perform the primary demodulation in the spread spectrum communication receiver, it is possible to realize lower power consumption and miniaturization compared to the conventional example in which the primary demodulation is performed using the differential detection method. .

[Brief description of drawings]

FIG. 1 is a block diagram of an SSC receiver according to an embodiment of the present invention.

FIG. 2 is a more detailed block diagram of the primary demodulation circuit shown in FIG.

FIG. 3 is a circuit diagram showing a specific example of a pulse amplifier following the primary demodulation circuit of FIG.

FIG. 4 is a block diagram of a delay detection circuit which is a conventional primary demodulation circuit.

[Explanation of symbols]

21: receiving antenna, 22, 24, 27, 36: amplifier, 23, 28, 35, 37: BPF, 25, 33: mixer, 26, 32: local oscillator, 30: SAW convolver, 31: buffer amplifier, 50: Primary demodulation circuit,
51: 90 ° phase shifter, 52: mixer, 53: low pass filter (LPF), 54: differential amplifier, 55: pulse amplifier.

Claims (2)

[Claims] 1. A spread spectrum communication receiver using a quadratcher demodulation circuit as a circuit for primary demodulating a secondary demodulated signal obtained by despreading and demodulating a received spread spectrum signal. 2. A surface acoustic wave convolver is used as a correlator for performing the despread demodulation.
The receiver for spread spectrum communication described.