JP3091385B2 - Phase modulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase modulation circuit used in a radio communication device, and more particularly, to an exclusive OR of a most significant bit (MSB) of a phase signal .theta. And each bit of a 2-bit gray code. The present invention relates to a phase modulation circuit that inverts the polarity of θ to generate a phase modulation wave.

[0002]

2. Description of the Related Art FIG. 1 is a block diagram showing an example of a configuration of a conventional circuit. In the figure, 1 is a cosine wave table, 2 is a sine wave table, 3 and 4 are carrier wave generation circuits, 5 and 6 are multipliers, 7 is an adder, 8 is a D / A converter, and 9 is a band pass filter (BPF). ). In the figure, a cosine value (cos θ) and a sine value (sin) are respectively obtained from a cosine wave table 1 and a sine wave table 2 by a phase signal θ input from the outside.
θ). These are input to multipliers 5 and 6, respectively, and carrier wave components sinω output from carrier wave generation circuits 3 and 4
_c t, multiplied with cos .omega _c t, is added by the adder 7. Since the output f (t) is expressed by the following equation (1), a phase modulation signal based on the phase signal θ is obtained.

[Number 1] _{f (t) = sinω c t} · cosθ + cosω c t · sinθ = sin (ω c t + θ) ......... (1) which was converted into an analog signal by a D / A converter 8, B
By extracting only necessary signals by the PF 9, a modulated wave can be obtained.

[0003]

[0006] However, in the conventional circuit configuration, the carrier _{(sinω c t, cosω c t} ) generation circuit 3, 4 and a multiplier 5 and 6 reduction in circuit scale due to the need for a low There is a limit in terms of power consumption, which is disadvantageous.

[0004] The present invention provides a phase modulation circuit which can solve the problems of the circuit scale and power consumption that occur in the conventional circuit configuration and can realize a reduction in circuit scale and a reduction in power consumption by simplifying the circuit. The purpose is to provide.

[0005]

SUMMARY OF THE INVENTION A phase modulation circuit according to the present invention receives an input phase signal .theta.
To output a phase modulation signal based on the input phase signal θ.
A phase modulation circuit that outputs 2-bit alternating binary code
A gray code generator that generates the input phase signal θ.
The most significant bit representing the polarity and the gray code generator
For each of the upper and lower bits of the 2-bit output
First and second Ex-Os that take exclusive OR and output
R circuit and the most significant bit of the input phase signal θ
1 of the phase signal φc replaced with the output of the Ex-OR circuit.
A cosine wave table for obtaining a cosine value ;
Placing the most significant bit at the output of the second Ex-OR circuit
A sine wave table for obtaining a sine value of the replaced phase signal φs,
An adder for adding combining the outputs of the sine wave table and the cosine wave table, a D / A converter for converting the adder output into an analog signal and spurious harmonics of the multiplied waves, etc. of the D / A converter output it is characterized in that a band-pass filter for extracting the phase modulated signal to remove.

[0006]

【Example】

(Configuration) FIG. 2 is a block diagram showing a configuration example of the present invention. In the figure, 21 is a gray code generator, 22 and 2
3 is an exclusive OR circuit (Ex-OR circuit), 24 is a cosine wave table, 25 is a sine wave table, 26 is an adder, 2
7 is a D / A converter and 28 is a BPF. FIG. 3 is a timing chart of the output of the gray code generator 21 of the present invention, in which indicates upper bits and indicates lower bits.

[0007] Gray code is a continuous number.
Is expressed in binary, the adjacent numbers are
It is an alternating binary code made to differ only in
You. Therefore, as shown in FIG.
1 is 1 / (4f), where f is the carrier frequency.
The upper bit is 1 higher than the lower bit
2 bits delayed by / (4f) (π / 2 in terms of phase)
Output the signal of

(Operation) The operation of the present invention based on the configuration example shown in FIG. 2 will be described below. Polarity of phase signal θ (data) given from outside
MSB (Most Significant Bit)
And an exclusive OR circuit 22 for each of the upper bit and the lower bit of the bit output of the gray code generator 21.
Ex-OR is taken at 23. And the polarity of the phase signal θ is displayed.
Only to MSB in the output of the Ex-OR circuits 22 and 23
Replace each . A phase <br/> signal the MSB is replaced respectively phi _c, and phi _s. That is, the phase signal
φ _c and phase signal φ _s are mutually 互 い _に of the carrier frequency.
This is a signal whose polarity is inverted at intervals. Lower phase signal θ
Bits correspond to the phase from the angle start value of each quadrant
I do.

[0009] The thus obtained carrier frequencies
The phase signal φ _c and the phase signal φ _s whose polarities are inverted at quarter intervals are input to a cosine wave table 24 and a sine wave table 25, respectively, to obtain a cosine value and a sine value. Are added and synthesized. Cosine wave tape
Cosine value (co
sφ _c ) and the sine value (sin φ _s ) are obtained by changing the polarities of the cosine value (cos θ) and the sine value (sin θ ) of the input phase signal θ to 1 / (2
f), the signal is inverted at a timing shifted by 1 / (4f) (π / 2 in terms of phase ).
A modulated wave is obtained through the addition and addition .

This is converted into an analog signal by the D / A converter 27. This waveform is output by the carrier wave sinω of the carrier generation circuits 3 and 4 in the conventional circuit shown in FIG.
_c t, is the same as that obtained modulated wave in the case of using the rectangular wave respectively cos .omega _c t. The output f (t) is as shown in FIG. 4 to that shown in FIG., The level 33 of the multiplier wave (3f _c in FIG. 4, 5f _c) odd carrier frequency f _c greater harmonic spurious exits. This can be expressed by the following equation: D / A converter 2
7, the output f (t) is as follows.

[0011]

(Equation 2)

[0012] Here, sgn [sinω _c t] and sgn [cosω _c t]
It is and sin .omega _c t respectively, from a waveform obtained by shaping the cos .omega _c t to a rectangular wave of 2 values can be Fourier expansion as follows.

[0013]

(Equation 3)

FIG. 4 shows the spectrum of the equation (2). From the expressions (3) and (4), the spectrum of the expression (2) is as shown by the hatched portion in FIG. That spectrum entire envelope is (sinx / x) shape, (cosine wave of the angular frequency omega _c, sine wave component) fundamental wave component and its odd multiple harmonics appear. The fundamental wave component of f (t) obtained by substituting the above equations (3) and (4) into the equation (2) is f ₁ (t)
If (k = 1), the following equation is obtained for f ₁ (t).

[0015]

(Equation 4)

This is equivalent to f (t) = sin (ω _c
(t + θ), but the waveform is the same but different.
That is, if harmonic components are removed by the BPF, a waveform similar to that using a sine wave and a cosine wave can be obtained even when a rectangular wave is used as a carrier wave. Therefore, a BPF 28 having a narrow-band characteristic 32 as shown in FIG. 4 is inserted after the D / A converter 27 in FIG. Spurs). As a result, a modulated wave that does not affect adjacent channels can be obtained.

FIGS. 5A and 5B are comparison diagrams of a modulated wave spectrum. FIG. 5A shows a modulated wave spectrum in the conventional circuit, and FIG. 5B shows a modulated wave spectrum in the circuit of the present invention. The measurement conditions are as follows. Modulation method: 4-level FSK Carrier frequency: f _c = 455 kHz Characteristics of BPF used: center frequency 455 kHz, pass bandwidth 17 kHz As shown, the experimental results according to the present invention may be equivalent to the results obtained from the conventional circuit. You can check.

[0018]

As described above, conventionally, the cosine value of the phase signal θ is
(cos [theta]), the carrier to the sine value (sinθ) sinω _c t, cosω
_Although the modulated wave is obtained by multiplying each of the _c t by using a multiplier, in the present invention, the MSB of the phase signal θ and 1 / (4f)
Ex with gray code (2 bits) switched every time
By taking -OR, the polarities of the sine and cosine values of θ are inverted every 1 / (2f), and the adder adds and synthesizes to obtain a modulated wave. Therefore, a carrier generation circuit and a multiplier are provided. Is not required, and the circuit scale can be reduced and the power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration example diagram of a conventional circuit.

FIG. 2 is a configuration example showing an embodiment of the present invention.

FIG. 3 is a timing chart of a gray code generator output according to the present invention.

FIG. 4 shows a modulated wave and its multiplied wave when a rectangular wave is used as a carrier wave.

FIG. 5 shows modulated wave spectra of a conventional circuit and a circuit of the present invention.

[EXPLANATION OF SYMBOLS] 1 cosine wave table 2 Sine wave table 3 sin .omega _c t generation circuit 4 cos .omega _c t generator 5,6 multiplier 7 adder 8 D / A converter 9 BPF 21 Gray code generator 22, 23 Ex −OR 24 Cosine wave table 25 Sine wave table 26 Adder 27 D / A converter 28 BPF 31 Modulated wave 32 Characteristics of bandpass filter (BPF) 33 Level of multiplied wave

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03C 3/00 H04L 27/12 H04L 27/20

Claims (1)

(57) [Claims] 1. An input phase signal represented by a digital value.
θ to output a phase modulation signal based on the input phase signal θ.
Gray code for generating a 2-bit output of an alternating binary code
A generator, a most significant bit indicating the polarity of the input phase signal θ, and
Upper bit, lower bit of 2-bit output of Gray code generator
Exclusive OR with each of the bits and output
The first and second Ex-OR circuits and the most significant bit of the input phase signal θ to the first Ex-OR circuit.
Obtain cosine value of phase signal φc replaced with output of OR circuit
Cosine wave table, and the most significant bit of the input phase signal θ is stored in the second Ex-
Obtain the sine value of the phase signal φs replaced with the output of the OR circuit
A sine wave table, an adder for adding and combining outputs of the cosine wave table and the sine wave table, and a D / A converter for converting the output of the adder to an analog signal.
Phase modulation circuit characterized in that a band-pass filter to remove spurious harmonics of the multiplied waves, etc. of the D / A converter output retrieving the phase modulation signal.