JP3259100B2 - Modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulator used in digital communication, and more particularly to a four-phase quadrature phase modulator.

[0002]

2. Description of the Related Art As is well known, in a four-phase quadrature phase modulator for forming a multi-channel transmission modulation wave having different frequencies of respective channels, it is necessary to maintain orthogonality in all of the multiple channels, that is, to maintain orthogonality. Bandwidth is required. Therefore, conventionally, for example, a configuration as shown in FIG.

In FIG. 2, P applied to an input terminal 1
The channel data is waveform-shaped by a low-pass filter (LPF) 3 and becomes one input of a mixer 5. The Q-channel data applied to the input terminal 2 is shaped by a low-pass filter (LPF) 4 and becomes one input of a mixer 6.

On the other hand, the output of the local oscillator 31 is branched into two by an in-phase distributor 32, one of which is output to the other input of the mixer 5, and the other is output to a 90 ° phase shifter 3
The phase is shifted by 90 ° at 3 and becomes the other input of the mixer 6.

That is, the P-channel data and the local oscillator 31
Is multiplied by the mixer 5, and the Q-channel data is multiplied by 90 ° in phase with the output of the local oscillator 31 by the mixer 6 to perform quadrature phase modulation.

The outputs of both mixers are combined by an in-phase combiner 34 to form a four-phase modulated wave, which is multiplied by the output of a synthesizer 36 by a mixer 35 to produce an IF signal having a frequency corresponding to the channel. This is subjected to a spurious elimination process by the band-pass filter 37 and transmitted to the transmission stage.

As described above, in the conventional four-phase quadrature phase modulator, the 90 ° phase shifter 33 controls the 90
Since it is very difficult to guarantee °, it is possible to handle multiple channels while maintaining 90 ° quadrature modulation by first performing 90 ° quadrature modulation at a fixed frequency and then setting the desired frequency by the synthesizer 36. To obtain a wide band output frequency.

[0008]

However, in the conventional four-phase quadrature phase modulator, spurious as an unnecessary wave is unavoidable in the mixer 35 for widening the band, so that the band for removing the spurious is unavoidable. Although it is necessary to provide the pass filter 37 at the output stage, spurious components coming into the band cannot be removed, and spurious components outside the band may not be sufficiently removed. That is, in the conventional four-phase quadrature phase modulator, there is a problem that spurious always exists in the modulator output, and in some cases, the line quality is adversely affected.

It is an object of the present invention to provide a modulator which enables an orthogonal wide band without generating unnecessary spurious.

[0010]

In order to achieve the above object, a modulator according to the present invention has the following configuration. That is, the modulator of the first invention is a modulator that performs four-phase quadrature phase modulation on P-channel data and Q-channel data waveform-shaped by a low-pass filter; A synthesizer for generating a frequency; a variable 90 ° phase shifter for performing an operation of shifting the output of the synthesizer by 90 ° in accordance with a correction signal; a first mixer for multiplying the P-channel data and the output of the synthesizer A second mixer for multiplying the Q-channel data by an output of the variable 90 ° phase shifter; a four-phase quadrature combining an output of the first mixer and an output of the second mixer; phase phase combiner and for outputting a phase-modulated wave signal; the phase error detecting circuit comprises a; detecting a quadrature phase error and the phase error detection circuit for output as the correction signal
Is the output of the first mixer and the output of the second mixer
A third mixer for multiplying and outputting the third mixer; and the third mixer
A loop filter for filtering the output of the filter;
The correlation between the P channel data and the Q channel data is
An exclusive OR circuit to take; and an output of the loop filter
And the output of the exclusive OR circuit, and the multiplication is performed.
A multiplier for outputting a result as the correction signal;
It is characterized by having.

[0011]

[0012]

Next, the operation of the modulator according to the present invention having the above structure will be described. In the present invention, four-phase quadrature phase modulation for P-channel data and Q-channel data is directly performed for each channel using a synthesizer. At this time, the 90 ° phase shifter is of a variable type, and the quadrature phase error is zero. The variable 90 ° phase shifter is controlled so as to be as follows.

As a result, since the four-phase quadrature-phase modulated wave signal of each channel is directly formed, unnecessary spurious as in the prior art can be prevented. Further, since the orthogonality is always maintained by controlling the variable 90 ° phase shifter, a wide band of the orthogonality is guaranteed, and the orthogonality variation due to temperature and aging during operation is always maintained. Since the correction operation is performed, the orthogonal accuracy is well compensated.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a modulator according to one embodiment of the present invention. In FIG. 1, a P-channel data applied to an input terminal 1 is shaped by a low-pass filter (LPF) 3 and becomes one input of a (first) mixer 5. Also, input terminal 2
Is applied to the low-pass filter (LP).
F) The waveform is shaped at 4 and becomes one input of the (second) mixer 6. The above is the same as the conventional case (FIG. 2).

On the other hand, the synthesizer 13 generates a frequency for each channel. A frequency signal of a certain channel is branched into two by the in-phase phase distributor 8, and one branch output becomes the other input of the mixer 5 and the other branch output. The branch output is phase-shifted by 90 ° by the variable 90 ° phase shifter 7 and becomes the other input of the mixer 6.

In short, the baseband data (P, Q) of each channel is quadrature-phase modulated, and directly converted to an IF signal of a frequency corresponding to each channel.

The output of the mixer 5 (6) is split into two by the in-phase splitter 16 (17), and one of the split outputs is synthesized by the in-phase synthesizer 9 to become a four-phase quadrature modulated wave. Since the above route has no spurious factors,
The output of the in-phase synthesizer 9 has no spurious as in the prior art. Therefore, the output of the in-phase synthesizer 9 is sent directly to a transmission stage (not shown).

Here, the variable 90 ° phase shifter 7 is controlled so that the phase shift operation thereof is exactly 90 ° as described later. , The orthogonality of the four-phase quadrature modulated wave is accurately maintained. Hereinafter, the operation of compensating the orthogonality by the phase error detection circuit will be described.

The other branch output of the in-phase distributor 16 (17) becomes the input of the (third) mixer 10. Here, assuming that the other branch output of the in-phase distributor 16 is Pcos ω ₀ t, the quadrature phase error is θ, and the other branch output of the in-phase distributor 17 is Q sin (ω ₀ t + θ), The output is as shown in Equation 1. Since the harmonic component contained in the output of the mixer 10 is removed by the loop filter 11, the signal [(PQ) from which the harmonic component has been removed is input to one input of the multiplier 12. / 2) sin θ] is input.

[0020]

P cos ω ₀ t · Q sin (ω ₀ t + θ) = (PQ / 2) sin 2ω ₀ t cos θ + PQ sin θ ｛(1 + cos 2ω ₀ t) / 2｝

On the other hand, P and Q, which are baseband channel data, are signals taking ± 1, respectively. The correlation between the two is obtained by an exclusive OR circuit 14, and the correlation result is output to the other end of the multiplier 12. Input.

Thus, the multiplier 12 removes the uncertain data component due to the P-channel data and the Q-channel data included in the output of the loop filter 11, and corrects only the quadrature phase error θ which is a DC analog amount. The signal is supplied to the variable 90 ° phase shifter 7 as a signal.

In the variable 90 ° phase shifter 7, the multiplier 12
, The operation phase shift amount with respect to the output of the synthesizer 13 is adjusted so that the phase becomes a predetermined value of 90 ° or less when the quadrature phase error θ is on the plus side, and When the error θ is on the negative side, the phase is 90.
It is variably set to a predetermined value of not less than °. The above correction operation controls the quadrature phase error θ to be always zero.

[0024]

As described above, according to the modulator of the present invention, four-phase quadrature phase modulation of P-channel data and Q-channel data is directly performed for each channel using a synthesizer. The phase shifter is of a variable type, and controls the variable 90 ° phase shifter so that the quadrature phase error becomes zero.

Therefore, according to the present invention, 4
Since the quadrature phase modulated wave signal is directly formed, it is possible to prevent generation of unnecessary spurious as in the related art. Further, since the orthogonality is always maintained by controlling the variable 90 ° phase shifter, a wide band of the orthogonality is guaranteed, and the orthogonality variation due to temperature and aging during operation is always maintained. Since the correcting operation is performed, there is an effect that the orthogonal accuracy is favorably compensated.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of a modulator according to an embodiment of the present invention.

FIG. 2 is a configuration block diagram of a conventional modulator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input terminal 2 Input terminal 3 Low-pass filter 4 Low-pass filter 5 Mixer 6 Mixer 7 Variable 90 ° phase shifter 8 In-phase phase distributor 9 In-phase phase synthesizer 10 Mixer 11 Loop filter 12 Multiplier Reference Signs List 13 synthesizer 14 exclusive OR circuit 16 in-phase distributor 17 in-phase distributor

Claims (1)

(57) [Claims] 1. A modulator for performing four-phase quadrature phase modulation on P-channel data and Q-channel data waveform-shaped by a low-pass filter; this modulator generates a frequency for each channel. A variable 90 ° phase shifter that performs an operation of shifting the output of the synthesizer by 90 ° according to a correction signal; a first mixer that multiplies the P-channel data by the output of the synthesizer; A second mixer for multiplying data by the output of the variable 90 ° phase shifter; and combining the output of the first mixer and the output of the second mixer to form a quadrature phase modulated wave signal. an output in-phase phase combiner; detecting a quadrature phase error and the phase error detection circuit for output as the correction signal; the phase error detecting circuit comprises a can, the
Multiplying the output of the first mixer by the output of the second mixer
A third mixer for outputting; and an output of the third mixer.
A loop filter for performing a filtering process;
Exclusion that takes the correlation between the channel data and the Q channel data
An OR circuit; an output of the loop filter and the output
Multiplies with the output of the other OR circuit and the multiplication result is
And a multiplier for outputting as a correction signal.
Modulator to be characterized.