JPH0350445B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] In order to maintain correct orthogonality between digitally orthogonally modulated signal components, a means for generating a 90° phase shifter error offset is provided in the orthogonal modulation input stage. .

[Industrial application field]

The present invention relates to a digital quadrature modulation circuit that can maintain orthogonality by canceling errors occurring in a 90° phase shifter.

[Conventional technology]

A conventional digital quadrature modulation circuit is constructed as shown in FIG. Quadrature modulation methods in digital quadrature modulation circuits include quadrature amplitude modulation, which includes 4-value QAM, 8-value QAM, and 16-value QAM, which are equivalent to 4-phase PSK. The operation of the quadrature amplitude modulation circuit will be explained below using 16-value QAM as an example.

16-value QAM simultaneously transmits 4 bits at each transmission time (clock cycle).The 4 bits are divided into 2 series of 2 bits each, and the value of each 2 bits of each series is determined. At one time, 4
Convert each digital signal into a digital signal that takes one of the values, and input each of the converted digital signals as digital modulation signals X and Y to one input terminal of mixers (balanced modulators) 2 and 3 shown in FIG. is input.
On the other hand, the carrier wave is input to the other input terminal of mixers 2 and 3, but the 90° phase shifter 1 is input to mixer 2.
A carrier wave delayed by 90° is input via Incidentally, in practice, it is common to provide the digital modulation signals X and Y with a low-pass filter to limit the band, but even in that case, the signals converge to four values every clock cycle.

If the carrier wave to mixer 2 is sinωt and the carrier wave to mixer 3 is cosωt, mixers 2 and 3
The outputs are Xsinωt and Ycosωt. These output signals are synthesized by the hybrid circuit 4, and Xsinωt
+Ycosωt. The signal arrangement is as shown in FIG. In other words, the carrier wave is changed according to the 4-bit signal.
The phase and amplitude indicated by one of 16 points are output.

In such an operation, if an error of δ occurs in the phase of the output signal of 90° phase shifter 1 with respect to the phase of the carrier wave to mixer 2, the output of mixer 3 will be Ycos (ωt + δ) = Ycosδcosωt −
Ysinδsinωt. Here, when δ is sufficiently small, it can be approximated by cos δ≒1 and sin δ≒δ. In that case, Ycos(ωt+δ)≈Ycosωt−Yδsinωt, and δ·Y arises as the sin component. Therefore,
The composite signal (orthogonally modulated signal) A is (X-δ・Y)
sinωt+Ycosωt, and an error of (-δ·Y) occurs in the X component of the transmitted signal, that is, the received signal. This situation is shown in FIG.

[Problem that the invention seeks to solve]

Adjustment of orthogonality by such means is difficult or impossible due to manufacturing reasons for the 90° phase shifter, such as modularization and mass production of modulation circuits. Naturally, this means that the degree of orthogonality between the orthogonally modulated signal components cannot be maintained at 90°.
This means that the desired orthogonally modulated signal cannot be transmitted.

The present invention was created in view of such problems, and provides a digital quadrature modulation circuit that can maintain orthogonality between signal components to be quadrature modulated even if there is an error in the 90° phase shifter. The purpose is to

[Means for solving problems]

FIG. 1 shows a block diagram of the principle of the present invention. In this figure, 7 is a coefficient unit, and 8 is an adder circuit. The digital modulation signal The circuit of the present invention is configured such that the signal is supplied to the quadrature modulation section 10. Note that the orthogonal modulation section 10 is equipped with a 90° phase shifter 1 for a carrier signal to be subjected to orthogonal modulation, as in the prior art.

[Effect]

The amount of weighting given to the digital modulation signal Y by the coefficient multiplier 7 is a value sufficient to generate an antiphase component with respect to the error component generated in the 90° phase shifter 1 of the quadrature modulation section 10. Therefore, even if an error occurs in the 90° phase shifter 1 and the degree of orthogonality between the orthogonally modulated signal components collapses, the above-mentioned weighting amount can be applied to the digital modulated signal Y. If a canceling component for the above-described error is generated in the modulated signal X, the degree of orthogonality between orthogonally modulated signal components is maintained.

〔Example〕

FIG. 2 shows an embodiment circuit of the present invention. This circuit 6 supplies one digital modulation signal Y to be orthogonally modulated to one input of an adder circuit 8A via a coefficient unit 7, and supplies the other digital modulation signal X to the other input of the adder circuit 8A. and synthesize it,
The composite signal and one digital modulation signal are supplied to respective inputs of the orthogonal modulation circuit 5 shown in FIG. 3. In this circuit 6, the coefficient multiplier 7 is preferably constructed as a weight-adjustable coefficient multiplier capable of adjusting the weighting applied to the digital modulation signal.

Next, the operation of the circuit of the present invention having the above configuration will be explained.

When there is no error in the 90° phase shifter 1 of the circuit shown in FIG. 2 and the output of the coefficient multiplier 7 is also adjusted to zero, the digital modulation signals X and Y are converted to the conventional orthogonal modulation shown in FIG. This is similar to orthogonal modulation in the circuit 5, and the output of the hybrid circuit 4, that is, the orthogonally modulated signal A is expressed as A=X+Ye ^{j x/2} , and the degree of orthogonality is maintained at 90°.

Assuming that an error of δ occurs in the 90° phase shifter 1 of the modulation circuit that generates such orthogonal modulation, the orthogonally modulated signal A′ is A′=X+Ye ^{j(x/2 +} 〓 ⁾ , and the orthogonality of the orthogonally modulated signal shifts by δ.

At this time, the weighting amount of the coefficient unit 7 on the signal Y is set to sinδ
When adjusted so that, the orthogonally modulated signal A'' at that time becomes A''=X+Ysin δ+Ye ^{j(x/2 +} 〓 ⁾ =X+Y jcosδ. In other words, the degree of orthogonality between the orthogonally modulated signal components is maintained at 90 degrees (see FIG. 6).

Thus, maintenance of orthogonality according to the invention is achieved without any adjustment of the 90° phase shifter 1.
Therefore, even if the 90° phase shifter 1 has no adjustment function at all, or even if it is placed in an environment where adjustment using the adjustment function is difficult or impossible, the orthogonality between the orthogonally modulated signal components can be adjusted to 90°. can be maintained at any time.

〔Effect of the invention〕

As described above, according to the present invention, the degree of orthogonality between orthogonally modulated signal components can be maintained at 90 degrees without any adjustment of the 90 degree phase shifter. This is particularly useful when quadrature modulators become modular and integrated circuits and can no longer rely on adjustment by a 90° phase shifter.

[Brief explanation of drawings]

Fig. 1 is a principle block diagram of the present invention, Fig. 2 is an embodiment circuit diagram of the present invention, Fig. 3 is a conventional circuit diagram, and Fig. 4 is a block diagram of the principle of the present invention.
The figure shows the signal point arrangement when the degree of orthogonality is 90°, Figure 5 shows the signal point arrangement when the degree of orthogonality is 90° + δ, and Figure 6 shows the signal point arrangement when the degree of orthogonality is 90° + δ. It is a signal point arrangement diagram in the case of In Figures 1 and 2, 1 is a 90° phase shifter;
7 is a coefficient unit, 8 is a synthesis circuit (addition circuit 8A), 1
0 is a quadrature modulation section.

Claims (1)

[Claims] 1. Two carrier waves different by 90 degrees from each other are created by a 90 degree phase shifter 1, the two carrier waves are modulated with two digital modulation signals, and the modulated signals are combined and output. In the digital quadrature modulation circuit, one digital modulation signal is transferred to the 90° phase shifter 1.
The coefficient corresponding to the phase shift error is supplied to the adder circuit 8 through the coefficient unit 7 and added to the other digital modulation signal, and the added signal and the above-mentioned one digital modulation signal are used for quadrature modulation. A digital quadrature modulation circuit characterized by: 2. The digital orthogonal modulation circuit according to claim 1, wherein the coefficient multiplier 7 is constructed as a weight-adjustable coefficient multiplier.