JP2650555B2 - Synchronous spread spectrum modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronous spread spectrum modulator, and more particularly, to a spread spectrum (hereinafter abbreviated as "SS") modulation using carrier modulation, a carrier and a spread code have a synchronous relationship. And a synchronous spread spectrum modulator.

[0002]

2. Description of the Related Art Recently, in SS communication, mobile communication using a multiple access method based on SS technology has reached a practical range. As is well known, radio resources are finite, so it is necessary to use frequencies effectively. In that respect, the SS signal can contribute to the improvement of the frequency use efficiency in principle. Because of that,
Since the SS signal is spread over a wide frequency band and the power spectrum density of the modulated wave is very small, it has little effect on other conventional communication radio waves, etc., and can be mixed in the existing communication frequency band. The utility in that respect is also great. For the above reasons, wireless communication by SS is also becoming familiar, and in the future, applications such as inter-mobile communication applications mounted on vehicles etc.
The future and development are expected.

[0003]

2. Description of the Related Art As shown in FIG. 1, a conventional synchronous type spread spectrum modulation apparatus has an output of a local oscillator (OSC) 9.
C (t) is converted to a phase locked loop (PLL) type angle modulation circuit 10.
And a clock signal of a spread code generator (PNG) 8, and are widely used. The configuration and operation of such a conventional device will be described with reference to the block diagram of FIG.

[0004] Information S (t) is supplied from an input terminal In to a voltage controlled oscillator (VCO) 13 via an adder 2, where angle modulation by an information signal is performed. The VCO output becomes an angle-modulated output signal fm (t) that is angle-modulated (here, a type of frequency modulation) by information, and supplied to a frequency divider 5 and a multiplier 7 for spread modulation. The frequency divider 5 is used to reduce the frequency shift in advance so as not to exceed the phase comparison range of the phase comparator 6, and functions to reduce the frequency of the input signal by the frequency division number N in principle. Phase comparator 6
Is widely used from a phase comparison range of ± π / 2 radians of an analog multiplication type to ± 2π radians of a digital type.

Since the frequency deviation Δf of the angle modulation output signal fm (t) is generally ± several tens of kHz, the phase comparison between the angle modulation output signal fm (t) and the local oscillation signal C (t) as it is is PLL (Phase Locke
d Loop) Synchronization becomes impossible, and correct angle modulation cannot be performed. Therefore, the frequency divider 5 having the frequency division number N is indispensable. The output signal fd (t) of the frequency divider 5 is supplied to the phase comparator 6, where the phase is compared with the output C (t) of the local oscillator (OSC) 9.

[0006] In angle modulation, since the modulation index m _f is represented as divided by the frequency shift Δf at the modulation frequency fm, in the phase comparator 6, when the phase comparison range in this case between ± [pi / 2, The modulation frequency fm at which the modulation index _MF is maximized is the lowest modulation frequency _fmL (for example, 30 Hz in the audio frequency). Therefore, the frequency deviation Δf / N of the frequency divider 5 is (ΔF / N ) ≦ (π /
2) Set to * f _mL . To explain with a practical example, VCO1
If the frequency shift of the angle modulation output from 3 is 8 kHz,
When the minimum modulation frequency f _mL is 30 Hz, the frequency division number N is about 170
Becomes

The output of the phase comparator 6 is a loop filter (L
F) VC as error signal Er (t) via 4 and adder 2
O13. Generally, the response of the loop is designed to respond in a frequency region lower than the information frequency band. Therefore, the VCO 13 performs frequency modulation by the information signal. The angle-modulated output signal fm (t) obtained in this way maintains a synchronous relationship with the local oscillation signal C (t).

The local oscillation signal C (t) is supplied to the spread code generator 8 as a clock signal to generate a spread code P (t). The obtained spread code P (t) is supplied to a multiplier 7, where spread modulation is performed by multiplication with the angle modulation output signal fm (t), and a spread spectrum (SS) modulated wave P (t) fm. (t)
Is output from the terminal Out. In the present device, the fact that the spread code P (t) in the SS modulated wave and the angle modulation carrier are kept in a synchronous relationship as described above is the reason why the device is called a synchronous SS modulator.

[0009]

As described above, the synchronous type S
When configuring the S modulator, the PLL angle modulation circuit 10 is used, and the frequency division number N of the frequency divider is essential in the PLL circuit. That is, since the frequency divider 5 exists between the VCO 13 and the phase comparator 6, the local oscillation output frequency supplied to the phase comparator 6 is multiplied by N to become the angle modulation output signal of the VCO 13, so that the local oscillation output Since the jitter in the signal and the output jitter of the VCO 13 are multiplied by N (here, 170 times) and increased, it is better not to increase the frequency division number N as much as possible.
There is a problem in that a device design with a shallow modulation factor, which is disadvantageous in terms of N, cannot be omitted.

[0010]

The present invention has been made in view of the above-mentioned problems.
It has been made Te, Re for adjusting the level of the information signal
Bell adjuster and angle modulator for primary modulating the information signal
And dividing the output signal from the angle modulator by 1 / N
A divider for obtaining a divided output, and a divided output from the divider
A phase comparison with the clock signal from the voltage controlled oscillator
A phase comparator and a loop filter from the phase comparator.
Output from the level adjuster and the output
Output an error signal of the
Subtraction for unmodulating the clock signal from the voltage controlled oscillator
And the unmodulated clock from the voltage controlled oscillator.
A spread code generator for generating a spread code by a clock signal;
The spreading code from the spreading code generator and the spreading code from the frequency divider
Multiplies the divided output to output a spread spectrum modulated signal
A synchronous spectrum, comprising:
A spread-spectrum modulator.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the synchronous spread spectrum modulator according to the present invention will be described with reference to the block diagram of FIG. In this figure, 12 is an angle modulator, 14 is a subtractor (subtraction circuit), 16 is a level adjuster, and other components that are the same as those of the conventional device shown in FIG. A detailed description thereof will be omitted.

The information S (t) from the input terminal In is supplied to the angle modulator 12 and the negative input terminal of the subtractor 14 via the level adjuster 16, respectively. If, for example, a voltage controlled oscillator (VCO) is used as the angle modulator 12, frequency modulation can be easily performed. The output signal fm (t) from the angle modulator 12 is
It is supplied to the frequency divider 15 and the multiplier 7 for spread modulation. A frequency-divided output fd (t) obtained by dividing the frequency by 15 is obtained from the frequency divider 15 and supplied to the phase comparator 6 constituting the inverse modulation circuit.

The phase comparator 6 compares the phase with the output of the VCO 11, and the phase comparison output is output from the loop filter 4 to the error signal of the loop and the divided frequency deviation Δf / N of the divided output fd (t). , And is supplied to the positive input terminal of the subtractor 14. Therefore, the subtractor 14
In, subtraction is performed with the information signal whose level has been adjusted by the level adjuster 16. As a result, the demodulated output d (t) is canceled, and only the error signal of the loop is supplied to the VCO 11.

By the canceling operation, the output of the VCO 11 becomes a non-modulated signal C '(t), which is supplied to the spread code generator 8 as a clock signal for generating a spread code. By supplying the obtained spread code P (t) to the multiplier 7, spread modulation is performed by multiplying the output signal fm (t) of the angle modulator 12, and the SS modulated output signal P (t) is obtained. fm (t)
Is generated and output from the output terminal Out.

As described above, a synchronous relationship is established between the carrier frequency of the angle modulation output and the spread code P (t), and the synchronous S
It will operate as an S modulator. The frequency divider 15
Unlike the frequency divider 5 used in the conventional example, the phase comparator 6
The phase comparison between the unmodulated VCO output C ′ (t) and the frequency-division-angle-modulated signal of the frequency divider 15 does not exceed the phase comparison range. Loop filter 4
Has a function of removing high-frequency components (doubled frequency components obtained by multiplying the VCO output frequency and the divided output frequency) from the output of the phase comparator, and a function of setting a loop response.

[0016]

As described in detail above, according to the present invention,
According to the phase spread spectrum modulator,
Spread code by unmodulated clock signal from control oscillator
Since the spread code is generated by the signal generator,
Multiplied by the spread code from the spread code generator
When the spread spectrum is performed by the calculator, the jitter
It is possible to output a spread spectrum modulated signal without components.
Can Ru.

[Brief description of the drawings]

FIG. 1 is a block diagram of a conventional representative synchronous spread spectrum modulation apparatus.

FIG. 2 is a block diagram showing an embodiment of a synchronous spread spectrum modulation apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Synchronous spread spectrum modulator 4 Loop filter (LF) 5, 15 divider 6 Phase comparator 7 Multiplier 8 PNG (Spread code generator) 10 PLL type angle modulation circuit 11, 13 Voltage controlled oscillator (VCO) 12 Angle modulator 14 Subtractor 16 Level adjuster

Claims (1)

(57) [Claims] 1. A level adjuster for adjusting a level of an information signal .
An angle modulator for primary-modulating the information signal;
Divides the output signal from the degree modulator by 1 / N and
A frequency divider, a frequency-divided output from the frequency divider, and a voltage control generator.
Phase comparator that compares the phase with the clock signal from the shaker
And an output of the phase comparator through a loop filter.
The output of the level adjuster is subtracted from the error of the loop.
And outputting the voltage control signal according to the error signal.
A subtractor for unmodulating the clock signal from the oscillator;
The unmodulated clock signal from the voltage controlled oscillator
A spreading code generator for generating a spreading code by
Spreading code from code generator and frequency-divided output from frequency divider
To output a spread spectrum modulated signal by multiplying
DOO synchronization characterized by comprising a type spread spectrum modulator.