JPH05153181A - Modulator - Google Patents

Abstract

PURPOSE:To always output a carrier wave whose phase difference is 90 deg. to a modulating part by adjusting the phase difference of the carrier wave automatically without intermediary of manual operation. CONSTITUTION:A first carrier wave C1 outputted from a carrier oscillator 6 is outputted to a first modulator 3, and simultaneously, it is outputted to a phase shifter 7. In the phase shifter 7, a second carrier wave C2 having the phase difference of 90 deg. from the first carrier wave C1 is generated, and this second carrier wave C2 is outputted to a second modulator 4. On the other hand, a detection control circuit 8 controls the phase shifter 7 so that the phase difference between the first carrier wave C1 and the second carrier wave C2 is always orthogonal, and changes the phase of the second carrier wave C2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulator, and more particularly to a modulator used in a digital carrier transmission system.

[0002]

2. Description of the Related Art Generally, a baseband signal obtained by converting a digital code such as voice or image into a signal as it is is not necessarily suitable for transmission on a transmission line. Therefore, conventionally, a modulator that converts this signal into a form suitable for the transmission path has been used. By the way, in the modulator used in the quadrature amplitude modulation method, the signal points corresponding to the input digital data must be correctly arranged on the phase plane, but they are orthogonal to each other as one of the important elements for the correct arrangement. There is carrier orthogonality.

A conventional quadrature amplitude device will be described below with reference to the drawings. FIG. 3 shows an example of a conventional 16-quadrature amplitude modulator. In the figure, input digital signals S1 and S
2, S3 and S4 are input to the digital-analog converters 1 and 2, then converted into four-valued baseband signals A1 and A2 and input to the modulators 3 and 4. The modulators 3 and 4 amplitude-modulate mutually orthogonal carrier waves C1 and C2 by baseband signals A1 and A2. Since the outputs B1 and B2 of the modulators 3 and 4 are obtained by amplitude-modulating mutually orthogonal carrier waves, a 16-value quadrature amplitude modulation wave can be obtained by combining the outputs B1 and B2 with the combiner 5. Further, reference numeral 6 in the figure is a carrier wave oscillator which outputs a carrier wave C1. Reference numeral 18 denotes a phase shifter which inputs the carrier wave C1 and outputs the carrier wave C2 having a phase difference of 90 °.

FIG. 5 shows an arrangement of signal points on the phase plane of 16-value quadrature amplitude modulation. FIG.
1 and C2 have a phase difference of 90 °, and FIG. 5B shows a case where the phase difference is not 90 °. When the phase difference between the carrier waves C1 and C2 is not 90 ° as shown in FIG. 5B, each signal point is not in the correct position as shown in FIG. 5A, which causes deterioration of the error rate characteristic. Therefore, in the modulator of FIG. 3, the phase shifter 18 can be adjusted so as to have the signal point arrangement of FIG.

FIG. 4 is a detailed diagram showing an example of the phase shifter 18 of FIG. In the figure, reference numerals 14 and 15 denote carrier wave input / output terminals, and the capacitors 10 and 12 and the coil 11 are configured so that the phase difference between the input / output terminals 14 and 15 is approximately 90 °. Reference numeral 19 is a variable capacitor, and the phase difference between the input and output terminals 14 and 15 is 90
The output modulated wave of the modulator of FIG. 3 has the signal point arrangement of FIG.

[0006]

In the conventional modulator, the variable capacitor 19 of FIG. 4 is adjusted to obtain the arrangement of FIG. 5A so that the error rate characteristic becomes the best. There is a problem in that the adjustment requires a lot of time by hand, and when the phase difference is changed due to an external factor such as temperature, the adjustment is required each time.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a modulator capable of automatically adjusting the phase difference of carrier waves without human intervention.

[0008]

In order to achieve the above object, the invention according to claim 1 includes a carrier output unit for outputting a carrier and a modulator for modulating the carrier with a baseband signal. In the carrier wave output unit, the carrier wave output unit outputs a first carrier wave, and the phase shifter inputs the first carrier wave and outputs a second carrier wave having a phase difference from the first carrier wave. A detection control circuit that controls the phase shifter to change the phase of the second carrier wave so that the phase difference between the first carrier wave and the second carrier wave is orthogonal to each other. According to a second aspect of the present invention, the modulator includes a pair of digital-analog converters having a plurality of digital data as inputs, and two columns of multi-valued bases output from the pair of digital-analog converters. A pair of modulators, each of which receives a band signal and modulates the first and second carriers by the two columns of multi-valued baseband signals, and an amplitude-modulated wave output from the pair of modulators are combined to be orthogonal to each other. And a combiner that outputs an amplitude-modulated wave.

[0009]

In the present invention configured as described above, the first carrier wave output from the carrier wave oscillator is output to the first modulator and the phase shifter. The phase shifter produces a second carrier having a 90 degree phase difference from the first carrier, and the second carrier is output to the second modulator. On the other hand, the detection control circuit changes the phase of the second carrier by controlling the phase shifter so that the phase difference between the first carrier and the second carrier is always orthogonal.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The same components as those of the conventional technique are designated by the same reference numerals, and detailed description thereof will be omitted. A modulator according to an embodiment of the present invention is configured to include a carrier wave output unit 50 that outputs a carrier wave and a modulator unit 60 that modulates the carrier wave with a baseband signal. Carrier wave output unit 50
Is a carrier wave oscillator 6 which outputs a first carrier wave C1, a phase shifter 7 which inputs the first carrier wave C1 and outputs a second carrier wave C2 having a phase difference from the first carrier wave C1, and The detection control circuit 8 changes the phase of the second carrier C2 by controlling the phase shifter 7 so that the phase difference between the first carrier C1 and the second carrier C2 is orthogonal. The modulator 60 outputs a pair of digital-analog converters 1 and 2 that receive the input digital signals S1, S2, S3, and S4, and outputs 2 from the pair of digital-analog converters 1 and 2.
A pair of modulators 3, 4 for inputting the multi-valued baseband signals A1, A2 of the columns and respectively modulating the first and second carriers C1, C2 with the multi-valued baseband signals A1, A2 of the two columns.
And the amplitude modulation wave B output from the pair of modulators 3 and 4.
1 and B2 and synthesizer 5 which outputs a quadrature amplitude modulated wave. The detection control circuit 8 receives the first carrier wave C1 from the carrier wave oscillator 6 and the second carrier wave C2 from the phase shifter 7.
Is input, and it is detected that the phase difference between the two orthogonal carrier waves C1 and C2 is deviated from 90 °, and a control signal is output to the phase shifter 7.

Now, the phase difference between the carrier waves C1 and C2 is (90
Considering the case of + θ) °, C1 = Asin wt, C
2 = Asin (wt + π / 2 + θ) = Acos (wt + θ)
Is represented. Here, A is the amplitude of the carrier wave, w is the angular frequency of the carrier wave, and θ is a deviation from 90 °. When C1 * C2 is calculated in the detection control circuit 8, C1 * C2 = A2 sin wt * cos (wt + [theta]) = A2 / 2 {sin (2 wt + [theta])-sin [theta]} (1).

The sin (2wt + θ) term in the equation (1) refers to a frequency component twice the carrier frequency, and the sin θ term corresponds to the error from 90 ° in the phase difference between the carrier waves C1 and C2. .. Therefore, in the detection control circuit 8, C1 × C2
After the calculation of, the low-pass filter is used to calculate the sin (2wt + θ) component of Eq.
When the doubled component is removed, only the -sin θ term in the equation (1) remains, and the term representing the error component remains, so this can be used as the control signal D for correcting the error from 90 °. on the other hand,
The phase shifter 7 changes the phase of the carrier wave C2 so that the phase difference between the carrier waves C1 and C2 is 90 °, and changes the phase amount according to a control signal from the detection control circuit 8.

FIG. 2 shows a detailed circuit of the phase shifter 7, and the same components as those in the prior art have the same reference numerals. Figure 2
13 is a variable capacitance diode, the capacitance of which is changed by the voltage applied across the variable capacitance diode. Therefore, the detection control circuit 8 generates the control signal D corresponding to the error θ from the phase difference 90 °, and this is When added to the control terminal 17, the capacitance value of the variable capacitance diode 13 changes, and the phase difference between the terminals 14 and 15 changes. Here, the terminal 16 and the resistor 9 are for giving a DC bias to the variable capacitance diode 13.

As described above, by providing the detection control circuit 8 and the phase shifter 7 for detecting the error of the phase difference between the carrier waves C1 and C2 from 90 °, the modulators 3 and 4 of the modulator of the present invention are provided. C1 and C2 having a mutual phase difference of 90 ° are always input.

In the above embodiment, the case of 16-value quadrature amplitude modulation has been described, but the present invention is not limited to this, and can be applied to all modulation detecting devices for modulating orthogonal carrier waves. is there.

[0016]

As described above, according to the present invention, a carrier wave oscillator that outputs a first carrier wave and a first carrier wave that is input and a second carrier wave that has a phase difference from the first carrier wave is output. Since the phase shifter and the detection control circuit that changes the phase of the second carrier by controlling the phase shifter so that the phase difference between the first carrier and the second carrier are orthogonal to each other, Even if the phase difference deviates from 90 ° due to external factors such as the above, the detection control circuit detects it and controls the phase shifter to correct the phase difference to 90 °, so it is automatically performed without human intervention. Since the phase difference of the carrier wave is adjusted, it becomes possible to always output the carrier wave having the phase difference of 90 ° to the modulator.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of a phase shifter according to an embodiment of the present invention.

FIG. 3 is a block diagram of a conventional modulator.

FIG. 4 is a circuit diagram of a phase shifter used in a conventional modulator.

5A is an explanatory diagram of a signal point arrangement in which the phase difference is 90 ° in the case of 16-value quadrature amplitude modulation, and FIG. 5B is the phase difference in the case of 16-value quadrature amplitude modulation, which is not 90 °. It is explanatory drawing of a signal point arrangement.

[Explanation of symbols]

 1, 2 ... Digital-analog converter 3, 4 ... Modulator 5 ... Combiner 6 ... Carrier oscillator 7 ... Phase shifter 8 ... Detection control circuit 9 ... Resistor 10, 12 ... Capacitor 11 ... Coil 13 ... Variable capacitance diode 14 Input terminal 15 Output terminal 16 Bias terminal 17 Control terminal 18 Phase shifter 19 Variable capacitor

Claims (2)

[Claims] 1. A modulator including a carrier wave output unit for outputting a carrier wave and a modulator unit for modulating the carrier wave with a baseband signal, wherein the carrier wave output unit outputs a first carrier wave. , A phase shifter which inputs the first carrier wave and outputs a second carrier wave having a phase difference with the first carrier wave, and a phase difference between the first carrier wave and the second carrier wave is orthogonal to each other. And a detection control circuit that changes the phase of the second carrier by controlling the phase shifter. 2. The modulator includes a pair of digital-analog converters having a plurality of digital data as inputs, and 2 output from the pair of digital-analog converters.
The multivalued baseband signal of the column is input, and the first and second
A pair of modulators for respectively modulating the carrier waves of the two columns with the multi-valued baseband signals, and an amplitude modulation wave output from the pair of modulators,
The modulator according to claim 1, further comprising a combiner that outputs a quadrature amplitude modulated wave.