JPH03267831A - Demodulation circuit for spread spectrum signal - Google Patents

Abstract

PURPOSE:To demodulate a spread spectrum signal with a simple circuit by eliminating a harmonic component in the output of a multiplier circuit multiplying a reception signal with the output of a delay circuit. CONSTITUTION:This demodulation circuit for a spread spectrum signal consists of a delay circuit 52 retarding a reception signal R(t) by the period T of a PN(Pseudo Noise) code, a multiplier 50 multiplying the output R(t-T) of the delay circuit 52 with the reception signal R(t) and a low pass filter 54. For example, a delay circuit having one period T of a PN code is formed by an analog delay line 52A and a digital circuit. That is, the reception signal passes through a low pass filter 52a, A/D-converted by an A/D converter 52b and the result is inputted to a shift register 52c. The output of the shift register is converted into an analog signal by a D/A converter 52d and the signal is outputted through a low pass filter 52e. Thus, a PN code synchronizing circuit and a carrier recovery circuit are not required and the spread spectrum signal is demodulated with simple constitution.

Description

[Detailed Description of the Invention] [Summary of the Invention] Regarding a demodulation circuit for a spread spectrum signal, the purpose of this is to demodulate a spread spectrum signal with a simple circuit. A delay circuit delays the received signal of the modulated signal by multiplying the transmitted data by a PN code by one cycle of the PN code, and multiplication that takes the product of the received signal and the output of the delay circuit. The configuration includes a circuit, and a filter that removes harmonic components in the output of the multiplication circuit and outputs transmission data.

[Industrial application field] The present invention relates to a demodulation circuit for spread spectrum signals.

There is spread spectrum communication in which a signal to be sent is multiplied by a P N (Psude No. 1se) code, modulated, and sent. The present invention relates to this demodulation.

[Conventional technology]

Conventionally, a circuit as shown in FIG. 3(a) has been used to demodulate a spread spectrum signal. The received signal R(1) becomes one input of the multipliers 10, 12.14, and the other input of these multipliers is the output bit (n) of the PN generator 30.
1/2 bit shifted by phase shifter 32, bit (n-1) shifted by 1 bit from the output bit, output pitch)
(n). After passing through the IF filter 20, the output of the multiplier IO enters the demodulator 22 and becomes a demodulated output D (t). The output of the multiplier 12.14 is envelope-detected by the detector 16.18 and becomes W,,W! in FIG. 3(C). The output will be like this. These enter the differential amplifier 24 and become an output as shown in the figure W. Point P is the convergence point, and W becomes positive or negative if O5 deviates from this point. After passing through the LPF 26, it enters the clock generator (VCO) 28, and generates the generated clock CLK.
The phase of is delayed or advanced so that point P is maintained.

The clock CLK enters the PN code generator 30 and generates a PN code. This is the same as the transmitter's PN code,
Therefore, when synchronized with the transmitter, the autocorrelation is maximum, and the third
Figure (C) W 1. Wt is the peak. The convergence point is located between these peaks, thus shifted by T/2.

When the PN code generator output shifted by T/2 by the phase shifter 32 is input to the multiplier 10, the transmitting/receiving side PN codes are synchronized and the maximum autocorrelation output is obtained. Received signal R(t)
If the data sent on the transmitting side is D(t) and the PN code multiplied by this is PN(t), then R(t) - 〇(t) ・
PN(t) ・cos(ωct+θ), and the output of the IF filter 20 is obtained by excluding PN(t) (made constant)
However, the output of the demodulator 22 becomes D (t) minus cos (ωct + θ).

The demodulator 22 is called a Gostas loop demodulator, and as shown in FIG. 3(b), it includes multipliers 32, 34, 36, a loop filter 38, an LPF 42 .
44. It consists of a VCO 40 and a 90° phase shifter 46. If the input is ±A cos (ωct+θ), the output of the 1 multiplier 32 is the product D (
t), the demodulated output becomes D(t) after all.

The cosωcL used for this demodulation is obtained by shifting the phase by 90° with a 90° phase shifter 46 to make it sinωct, and applying this to the Q multiplier 3 through a loop filter 38 to the VCO 40.
It can be obtained by setting θ-0. θ = [Problem to be solved by the invention] As shown in Figure 3, demodulation of a spread spectrum signal requires the following steps:
A PN code synchronization circuit such as a DLL and a carrier regeneration circuit such as a Costas loop are required, and there is a problem that the hardware scale increases.

The object of the present invention is to improve these points and demodulate a spread spectrum signal using a simple circuit.

(Means for Solving the Problems) As shown in FIG. 1, in the present invention, the received signal R(t) is
A demodulation circuit for a spread spectrum signal includes a delay circuit 52 that delays the period T of N codes, a multiplier 50 that multiplies the output R(t-T) of the delay circuit 52 and the received signal R(t), and a low-pass filter 54. Configure.

[Operation] With the configuration of this if diagram, it is possible to demodulate a spread spectrum signal. To explain this, the output of the multiplier 50 is R(t)-R(t-T) = D(t)-PN(t).
cos(ωct 10)・D(t-T)・PN(L-T)
・cos(ωc(t-T)10)＼, PN(t)=
PN(t-T), PN(t)・PN(t) = 1
.

If ωcT=n・2π (n is an integer), the above formula becomes = D
(t) ・D (L-T)-cos” (ωct+θ)
become. When this is filtered to remove the cos2ωct component, it becomes =D(t)·D(t-T). Therefore, on the transmitting side, if the data string to be actually transmitted is T(t), D (t) = T (t)・D
If D (t) is determined by performing the operation (t-T) (if the product of the previous transmission data and the data to be transmitted this time is the current transmission data), D (t)・D < t-r )−T (t)・D (t
-T)·D (t-T)=T (t), and the receiving side obtains the transmission data T (t). In other words, demodulation is possible.

[Example] FIG. 2 shows an example of the present invention. In (a), a delay circuit for one cycle T of the RN code is configured with an analog delay line 52A.

(Matara) consists of digital circuits. That is, after passing the received signal through a low-pass filter 52a, the A/D converter 52b
The signal is A/D converted and input to the shift register 52c. The output of this shift register is converted into analog by a D/Ai converter 52d and outputted through a low-pass filter 52e. The delay time is, of course, determined by the number of stages through which data is shifted through the shift register and the period of the shift clock.

On the transmitting side, differential logic between data having the same delay time as the period of the PN code and current data may be used.

It becomes possible to demodulate a spread spectrum signal with this configuration.

[Brief explanation of drawings]

FIG. 1 is a principle diagram of the present invention, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a block diagram and waveform diagram showing a conventional example. In Figure 1, R(t) is the received signal, D(t) is the demodulated output,
50 is a multiplication circuit, and 54 is a filter.

Claims (1)

[Claims] 1. The product of the data sent in the previous cycle and the data sent this time is taken as the transmission data of the current cycle, multiplied by a PN code, and the received signal (R( t)), P
A delay circuit (52) that delays the N code by one period (T), a received signal (R(t)) and an output of the delay circuit (R(t-T))
); and a filter (54) that removes a modulated wave component in the output of the multiplication circuit and outputs transmission data. .