JPH02174343A - Orthogonal modulator - Google Patents

Abstract

PURPOSE:To improve the accuracy of orthogonal modulation by applying a variable phase shifter as a phase shifter used for forming a carrier signal, detecting a phase difference of two carrier signals in the case of being given to each modulator and controlling the phase shift of the variable phase shifter in response to the phase difference. CONSTITUTION:A carrier signal is given to a variable phase shifter 11 to form 1st and 2nd carrier signals, they are given respectively to corresponding 1st and 2nd modulators 3, 4, and 1st and 2nd modulation signals and the 1st and 2nd carrier signals are subject to modulation processing. The phase difference of the corresponding 1st and 2nd carrier signals given to the 1st and 2nd modulators 3, 4 is desired to be a reference phase difference pi/2. The phase difference of the 1st and 2nd carrier signals is detected by a phase comparator 10 to give it to the variable phase shifter 11 as a phase shift control signal so as to form a feedback loop thereby making the phase difference of the 1st and 2nd carrier signals to be pi/2 at all times independently of the change in the carrier frequency. Thus, the modulation accuracy is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a quadrature modulator, for example, a so-called I''DMA (Fre
Quc, ncy Division Multiple
It can be applied to a transmitting device of a transmission system (Access).

Conventional technology 1 FI for digital data M A (Four phase 1 which is one aspect of orthogonal modulation as a modulation method for p transmission) S K (Pt+asc 5hift Ke
ying) modulation method is used. Figure 2 shows an example of a conventional 4-phase PSK transformer, supervised by Moriji Kuwahara.
"Digital Microwave Communication", published by Kikaku Center Co., Ltd., May 1980, ppl O-111).

In FIG. 2, first and second modulated signals consisting of digital data are input to input terminals 1 and 2, respectively;
Each of these first and second modulators has a corresponding O
/π modulators 3 and 4.

On the other hand, a carrier wave signal having a predetermined frequency is input to the input terminal 5. This input carrier wave signal is given to a branching circuit 6, where it is branched into two identical carrier wave signals and output. One branched carrier wave signal (first carrier wave signal) is directly given to the first 0/π modulator 3. The other branched carrier signal (second carrier signal) is π/
The phase is shifted by π/2 through the two-phase shifter 7 and the second 0/π
is applied to modulator 4.

Thus, the phases of the first and second carrier signals for each 0/π modulator 3.4 differ by a reference phase difference of π/2.

Each of the 0/π modulators 3, .1 is composed of, for example, a ring modulator. Each 05/π change j, l device 3.4 respectively receives the input first or second change, il! , l signal 1), the carrier wave signal obtained by °ζ,'j- is outputted as is, or the phase of the carrier wave body is outputted with a shift of π. Each 0/π change'';, the changed JjJ signals from the single unit 3.4 are both sent to the synthesis circuit 8, and are synthesized by this synthesis circuit 8, resulting in a 4-phase 11) S K change''! It is output from output terminal 0 as an output signal of the 11 devices.

In other words, the phase changes by 0, π/2, π, or 3π/2 depending on the combination of logic levels of the first and second modulation signals input to the input terminals] and 2. 144
11) The SK variable-ara signal is output.

[Problem to be Solved by the Invention 1 The above-mentioned four-phase)] In a quadrature modulator such as an S K modulator,
Two carrier signals whose phases differ by a reference phase difference of π/2 are used as a core, and in the case of many quadrature modulators, the carrier wave signal of l flail is branched as described above and 211! l
By forming a carrier wave signal and shifting the phase of one of them by π/2, two orthogonal carrier waves No. 16 are formed.

π used to form two orthogonal carrier signals
As the /2 phase shifter, a delay circuit, a π/2 branch line coupler, or the like is actually used.

π formed by such delay circuits and branch line couplers, etc.
In the /2 phase shifter, the amount of phase shift generally varies from the reference amount of phase shift π/2 due to changes in carrier frequency.

For example, in FDMA transmission, the above-mentioned orthogonal variation J! , when applying an I-device, it is necessary to vary the carrier wave frequency in response to channel changes, but in this case, usually, a phase shift of π/2 with respect to the carrier wave frequency of the center channel is used. Apply the device. If this π/'2 phase shifter is formed, for example, by a delay line such as a coaxial cable, this delay line is I? Since an attempt is made to achieve the same delay time when changing the carrier frequency involved in DMA transmission, the amount of phase shift deviates by π/2 in channels other than the central channel. Now, assume that the carrier wave frequency is changed by about 10% from the carrier wave frequency of the center channel A. In this case, the phase shift error of the phase shifter is (π/2)Xo.

It becomes 1.

The present invention has been made in consideration of the following points,
An object of the present invention is to provide a quadrature modulator that can increase the precision of variation by suppressing the phase shift error of a phase shifter provided for forming two carrier signals that differ by a reference phase difference of π/2. It is something.

[Means for Solving the Problems 1] In order to solve the problems, the present invention includes a first transformer that transforms the first modulated signal by a first carrier signal, and a second A quadrature modulator that is separated from a second modulator that modulates a modulated signal by a second carrier signal by at least pjh is provided with the following parts.

That is, the phase comparator detects the phase difference between the first and second carrier signals, and the phase comparator detects the phase difference between the first and second carrier signals so that the reference phase difference is π/2. A variable phase shifter is provided which shifts the phase of the first and/or second carrier signal according to the phase difference obtained and outputs the phase to the first and/or second modulator.

[Operation] By passing the carrier wave signal through the variable phase shifter, first and second carrier wave signals are formed and applied to the corresponding first and second modulators, respectively. 1jf
At 74, the first and second modulation signals and the first and second carrier signals are modulated.

It is desired that the phase difference between the corresponding first and second carrier signals given to the first and second modulators is a reference phase difference of π/2. Therefore, a phase comparator detects the phase difference between these first and second carrier signals and supplies it to the variable phase shifter as a phase shift amount control signal, forming a feedback loop that is related to changes in carrier frequency. No, the first
and the second carrier waves 1 and 1 so that the phase difference is always π/2.

[Embodiment] Hereinafter, an embodiment in which the present invention is applied to four-phase (1) SK modulation (1) will be described with reference to the drawings.

Here, FIG. 1 is a block diagram showing the configuration of this embodiment, and parts corresponding to those in FIG. 2 described above are designated by the same reference numerals. Further, FIG. 3 is a characteristic curve diagram showing the human output characteristics of the phase comparator of this embodiment, and FIG. 4 is a characteristic curve diagram showing the input/output characteristics of the variable transfer device of this embodiment.

As shown in FIG.
7.1 device also basically uses first and second modulated signals inputted through input terminals 1 and 2, and first and second carrier waves whose phase is 5'4 by π/2 with respect to each other. The signals are modulated by first and second 0/π modulations 21) 3 and 4, and the modulated signals from j:) to tt f, - are synthesized by a synthesis circuit 8, and an 11-phase PsK is generated from an output terminal 9. It is sent 111 as the output signal of the modulator.

In the case of this embodiment, a configuration is provided for controlling so that the difference of the order of 4 (1) between the first and second carrier signals becomes accurate to the required reference phase difference π/2.

That is, the first and second carrier signals given to the first and second 0/π modulators 3 and 4 are input, and the
A phase comparator 10 is provided to detect a phase difference between the carrier signal and the second carrier signal. This phase comparator 10 outputs a voltage signal of 1E'' according to the phase difference.

FIG. 3 shows the phase delay (phase difference) of the second carrier signal with respect to the first carrier signal input to the phase comparator 10;
It is a characteristic curve diagram which shows the relationship with the voltage signal which phase comparison 'a10 outputs. As shown in Fig. 3, when the phase difference is the required reference phase difference π/2, O
When the phase difference is smaller than the reference phase difference π/2, it outputs a voltage signal that increases positively along the cosine wave shape as the phase difference becomes smaller, and the phase difference becomes the reference phase difference π/2. When it is larger than /2, a voltage signal that becomes negative along a cosine wave shape as the phase difference becomes larger is output. Although FIG. 3 also shows a case where the phase difference is greater than or equal to π, which is significantly different from the reference phase difference π/2, in practice, such a phase difference rarely poses a problem.

In this way, the voltage signal output from the mu gamma phase ratio 1 articulator 10 is the second carrier wave 1. -Used as a control signal to adjust the phase of the ζ signal.

In this embodiment, the second carrier signal is formed by shifting the phase of one of the carrier signals branched out by the branching circuit 6 by approximately π/2 via the variable phase shifter 11. The voltage signal output from the phase comparator 10 is applied to the variable phase shifter 11 as a phase shift amount control signal via a loop filter circuit 12 consisting of 18 fM V-pass filter circuits. 11 varies the amount of phase shift according to the applied voltage signal.

That is, as shown in FIG. 4, the variable transfer device 11 sets the reference value π/2 as the phase shift amount when the voltage signal from the loop filter circuit 12 is 0, and sets that value when the voltage signal is positive. As becomes larger, the phase shift amount is made larger than the reference phase shift amount π/2, and when the voltage signal is negative, as the value becomes smaller, the phase shift amount is made smaller than the reference phase shift amount π/2.

Note that the voltage signal output from the phase comparator 10 is not directly applied to the variable phase shifter 11, but instead is applied to the loop filter circuit 12.
The reason why the phase comparator 10 is provided through the loop filter circuit 12 is to remove unnecessary spectra generated by the phase comparator 10, noise mixed in, etc.
This is because the control speed of the loop described above for controlling the phase difference of the second carrier signal to the reference value is not a core response or a slow response, but a response of an appropriate speed.

In the above configuration, the second carrier signal has a phase difference φ1 larger than the reference phase difference π/2 with respect to the first carrier signal.
Suppose that it has a.

At this time, the phase comparator 10 outputs a voltage signal with a negative value via corresponding to the phase difference φ1a according to the characteristic curve shown in FIG. This voltage signal (via) is applied to the variable phase shifter 11 after being filtered through the loop filter circuit 12 . At this time, the variable phase shifter 11 is
The input voltage signal (-vlb;-vll) is -V L
After filtering Fi), set the phase shift amount according to
The value φ1. shown in FIG. 4 is smaller than the reference phase shift amount π, /2.
l).

Thus, the first. Conversely, when the phase difference between the second carrier signal and the second carrier signal is larger than the reference phase difference π/2, the variable phase shifter 1
The phase shift 1ti of 1 is set to a value smaller than the reference phase shift amount π/2, and the feedback 1ri1 is determined so that the phase difference becomes -L(quasi-phase difference π/2).

Moreover, the second carrier wave body with respect to the first carrier wave signal is
Assume that the phase difference φ221 is smaller than the reference phase difference π/2. At this time, the phase comparator 10
Not shown in the figure 1. According to the ν characteristic curve, a voltage signal having a positive value v 2 a corresponding to the phase difference φ2 Q is output. This voltage signal (v 2 a ) is filtered through the loop filter circuit 12 and then applied to the variable phase shifter]1. At this time, the variable phase shifter 11 outputs the input voltage 1
3 (v2b; V21] is the value obtained by filtering V2a), the phase shift amount is varied to a value φ2b shown in FIG. 4, which is larger than the reference phase shift rat π/2.

Thus, when the phase difference between the first and second carrier signals is smaller than the reference phase difference π/2, the phase shift amount of the variable phase shifter 11 is set to a value larger than the reference phase shift amount π/2, Feedback control is performed so that the reference phase difference is π/2.

Therefore, according to the above-described embodiment, the phase difference between the first and second carrier signals can be feedback-controlled to the reference phase difference of π/2, and from this point the accuracy of orthogonal modulation can be improved. be able to.

Furthermore, even if this embodiment is applied to a l''DMA1 transmission system in which the carrier wave frequency frequently changes, the phase difference control loop will function, so the phase difference will not change despite the fluctuations in the carrier wave frequency. can be controlled to a reference phase difference of π/2, and modulation accuracy can be improved.

Note that in the above embodiment, the second
Although the configuration is shown in which the variable phase shifter 11 is provided in order to form the first carrier signal, a configuration in which the variable phase shifter is provided in order to form the first carrier signal on the phase leading side may also be used. In addition, a configuration may be adopted in which a variable phase shifter of 2 ([7!1) is provided to form the first and second carrier signals. In short, two carrier waves with a phase difference of π/2 The present invention can be applied to devices having a configuration in which a phase shifter is interposed so as to form a signal.

In addition, in the above-mentioned embodiment, the present invention is applied to a four-phase P S
Although the embodiment has been shown to be applied to a K modulator, it is of course applicable to other types of orthogonal modulation 2:).

Furthermore, although the present invention is particularly effective when applied to a transmitting device in which the carrier frequency is switched in response to switching of the transmission channel, it can also be applied to a transmitting device with a fixed channel.

[Effects of the Invention] As described above, according to the present invention, a variable phase shifter is applied as a phase shifter used to form at least one carrier wave signal, and two carrier waves are applied to each modulator. Since the phase difference of 1 word V) is detected and the phase shift amount of the variable phase shifter is controlled according to the phase difference, the phase difference between the two carrier signals can be used as the reference phase difference that is constantly determined. π/2, and the accuracy of orthogonal modulation can be improved compared to the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a quadrature modulator according to the present invention, FIG. 2 is a block diagram showing a conventional quadrature modulator,
FIG. 3 is a curve diagram showing the input/output characteristics of the phase comparator 10 of the above embodiment, and FIG. 4 is a v curve diagram showing the input/output characteristics of the phase comparator 10 of the above embodiment.
FIG. 1 is a characteristic curve diagram showing the input/output characteristics of No. 1; 1.2...Modulation signal input terminal, 3.4...0/π modulator, 5...Carrier signal input terminal, 6...Branch circuit, 8...Composition circuit, 9... Transduced 1 signal output terminal,
10... Phase comparator, 11... Variable phase shifter. Patent applicant Oki Electric Industry Co., Ltd.

Claims (1)

Claims: At least a first modulator that modulates a first modulation signal with a first carrier signal; and a second modulator that modulates a second modulation signal with a second carrier signal. a phase comparator for detecting a phase difference between the first and second carrier signals; and a phase difference between the first and second carrier signals is a reference phase difference π.
/2, according to the phase difference detected by the phase comparator, and outputs the phase-shifted first and/or second carrier signal to the first and/or second modulator. A quadrature modulator comprising a phase shifter.