JP3316232B2 - MSK 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 an MSK modulation circuit used for satellite communication and mobile communication.

[0002]

2. Description of the Related Art In recent years, as a digital modulation method used for satellite communication and mobile communication, there is MSK (Minimum Shift Keying) modulation that enables narrowband communication with a constant envelope. This MSK modulation is described in, for example, pages 156 to 161 of “Spread Spectrum Communication System” published by Science and Technology Publishing Company.
Page.

FIG. 2 shows a conventional MSK modulation circuit. Input terminal 1 receives binary (± 1) I-axis input data having a transmission rate of ＴT. Input terminal 2 receives Q-axis input data delayed by T from I-axis input data. A first oscillator 3 generates a weighted sine wave having a frequency fs = 1 / 4T, and performs weighting by multiplying the I-axis input data by a third multiplier 4. The output of the first oscillator 3 is phase-shifted by 90 ° by the first phase shifter 5, and the output is multiplied by the Q-axis input data by the fourth multiplier 6 to be weighted. Third
The output of the multiplier 4 is further multiplied by a fifth multiplier 7 with a carrier having a frequency fc generated by a second oscillator 8. The output of the fourth multiplier 6 is multiplied by the sixth multiplier 10 with the carrier wave shifted by 90 ° by the second phase shifter 9. The outputs of the fifth and sixth multipliers are added by the adder 11 and output from the output terminal 12 as an orthogonally modulated MSK signal.

[0004]

In the above-described MSK modulation circuit, a well-known double-balanced operational amplifier is used for each multiplier. By using this double-balanced operational amplifier, the potential of the working pair is balanced, and the modulated wave and the carrier wave leakage can be minimized.

However, when using this double-balanced operational amplifier, the DC bias of the input of the operating pair must be cut because the DC bias of the operating pair is fixed. Therefore, if the binary input does not become 0 on average, MSK can be performed well.
There was a disadvantage that modulation was not possible.

The present invention has been made in view of the above points, and provides an MSK modulation circuit that can apply MSK modulation satisfactorily regardless of the pattern of input binary data.

[0007]

According to the present invention, there is provided a first multiplier having two output terminals having phases different by 180 ° and multiplying a cosine component of a weighted sine wave by a cosine component of a carrier;
A second multiplier having two output terminals having different phases by 80 ° and multiplying a sine component of a weighted sine wave by a sine component of a carrier; and the first multiplier controlled by first input binary data, A first selecting means for selecting one of the two output terminals, a second selecting means controlled by second input binary data and selecting one of the two output terminals of the second multiplier, An MSK modulation circuit comprising an adder for adding an output of the first selection means and an output of the second selection means to output an MSK signal.

[0008]

The MSK modulation circuit of the present invention multiplies the weighted sine wave by the carrier first, and then multiplies the input binary data by a multiplier instead of multiplying the input binary data by a multiplier.
Select the outputs of the multipliers with different phases. Then, an MSK signal is obtained by combining the outputs.

That is, when the cosine component of the weighted sine wave is multiplied by the cosine component of the carrier wave, the output is cos (πt / 2T) cos (2πfct). (2) When the sine component of the weighted sine wave is multiplied by the sine component of the carrier wave, the output is sin (πt / 2T) sin (2πfct). 2πfct) (4)

Then, the output (1) or (2) is selected according to the polarity of the I-axis input data, and the output (3) or (4) is selected according to the polarity of the Q-axis input data, and the two are synthesized. An MSK modulation circuit can be realized completely equivalently to the conventional one. As a result, the input of the multiplier is only a sine wave, and the output signal is always constant and independent of the input data.

[0011]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a quadrature modulation circuit according to this embodiment. The same parts as those in FIG.

In this embodiment, the output of the first oscillator 3 for generating a weighted sine wave and the output of the second oscillator 8 for generating a carrier are constituted by a double balanced operational amplifier having output terminals inverted by 180 ° from each other. Multiplied by one multiplier 13.
The two outputs of the first multiplier are supplied to the first switch 14, and are selected and output according to the I-axis input data.

On the other hand, the outputs of the first and second phase shifters 5 and 9 are also multiplied by a second multiplier 15 having the same configuration as the first multiplier 13 and selected by a second switch 16 based on the Q-axis input data and output. Is done.

The outputs of the first and second multipliers are added by an adder 11 and output as an MSK signal.

With the above configuration, a switch can be used instead of a multiplier for multiplying input data, although the circuit is completely equivalent to the conventional example of FIG.
The input of the second multiplier is a sine wave only, and the output signal is always constant and independent of the input data.

Therefore, the MSK modulation operation can be performed well even if the input data does not become 0 on average.

[0017]

According to the present invention, since the input of the multiplier can be only a sine wave, MSK modulation can be performed well even if the input binary data does not become zero on average.

Although four multipliers using a double balanced operational amplifier have conventionally been used, the present invention can be composed of two multipliers and two switches, so that the circuit configuration is simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram of an MSK modulation circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional MSK modulation circuit.

[Explanation of symbols]

 3 1st oscillator 5 1st phase shifter 8 2nd oscillator 9 2nd phase shifter 11 adder 13 1st multiplier 14 1st switch 15 2nd multiplier 16 2nd switch

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-239245 (JP, A) JP-A-60-208146 (JP, A) JP-A-5-63742 (JP, A) 63741 (JP, A) JP-A-61-39754 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04L 27/00

Claims (2)

(57) [Claims] A first multiplier for multiplying a cosine component of a weighted sine wave by a cosine component of a carrier wave, and two output terminals having a 180 ° phase different from each other; A second multiplier for multiplying the sine component of the weighted sine wave by the sine component of the carrier wave; 1 selecting means, second selecting means controlled by second input binary data and selecting one of two output terminals of the second multiplier, output of the first selecting means and output of the second selecting means And an adder for outputting an MSK signal. 2. The MSK modulation circuit according to claim 1, wherein said first and second multipliers are constituted by a double balanced operational amplifier.