JPH03104357A - Multi-value polyphase modulator - Google Patents

Abstract

PURPOSE:To eliminate the need for the adjustment of a phase of a carrier and an amplitude of a base band signal by providing a carrier address generating section generating an m-bit carrier address, an ROM outputting a multi-value polyphase digital modulation wave in response to an input address of an n-bit data series and a D/A converter. CONSTITUTION:A carrier address generating section 1 generates an m-bit carrier address of a prescribed sampling period and an ROM 2 receives an n-bit data series consecutive timewise and an m-bit carrier address and outputs a multi- value polyphase digital modulation wave accordingly and a D/A converter 3 applies D/A conversion to the multi-value polyphase digital modulation wave. Moreover, two orthogonal amplitude components are calculated from n-bit data series in advance and a sine wave component and a cosine wave component represented by an m-bit carrier address are multiplied with the result for the synthesis and the result is stored input address to the ROM 2.

Description

[Detailed description of the invention] [Summary] Quadrature amplitude modulation (QAM) and phase modulation (PSI) of communication equipment
Regarding the multilevel multiphase phase modulator in C), the purpose is to eliminate the need to adjust the amplitude of the baseband signal and the phase of the carrier wave in the modulator, and to enable output of a modulated wave at a higher frequency, with a constant sampling period. a carrier wave address generation unit that generates an m-bit carrier wave address, and a multi-level multiphase digital modulated wave corresponding to the human-powered address, using the m-bit carrier wave address and a temporally continuous n-bit data sequence as a manual address. and a D/A converter that D/A converts the multivalued multiphase digital modulated wave output of the ROM,
For M, two orthogonal amplitude components are calculated in advance from the temporally continuous n-bit data series, and a sine wave component and a cosine wave represented by the m-bit carrier address are added to each of the two amplitude components. The m-bit carrier address and the temporally continuous n-bit data series are configured to store a calculated value obtained by multiplying the components and summing the two multiplication results as input addresses, and further, R
The apparatus is configured to include an impulse generation circuit that converts the output of the OM or the output of the D/A converter into an impulse at the sampling period.

[Industrial application field]

The present invention relates to a multilevel multiphase phase modulator using quadrature amplitude modulation (QAM) for a communication device.

[Prior art] The polyphase phase modulation (PSIC) method using QAM independently amplitude modulates carrier waves sin wt and cos wt, which are orthogonal to each other, and then combines them to generate a polyphase phase modulated wave. Among these, selected modulated waves are transmitted, and QPSK, an example of which, is shown in FIG.

In FIG. 11, reference numeral 11 denotes a serial-to-parallel converter that converts two series of digital data, an E-channel (synchronous component) and a Q-channel (orthogonal component), into serial-to-parallel data. ) to generate parallel digital data.

Reference numeral 12.13 is a digital filter for waveform shaping, which is constituted by a ROM, for example, and reference numeral 14.15 is a D/A converter for D/A converting each 8-bit waveform-shaped data. The analog signal D/A converted by the D/A converter 14.15 is sent to a low-pass filter 16.17, where a baseband signal with the same amplitude for I and Q is generated. The carrier wave signal (for example, sin wt) from the reference oscillator 21 and the baseband signal of the ■ series are input to the mixer 18, and the carrier wave signal is amplitude-modulated. A carrier signal (e.g. cos wt) which is the output of the 90° phase shifter 22 which is orthogonal to the signal (e.g. sin wt) and Q
The carrier signal is amplitude modulated by inputting the baseband signal of the series.

These modulated waves with different phases by 90″ are generated by the hybrid circuit 2.
They are combined at 0 to form a four-phase modulated wave. Note that 23 is a bandpass filter that selects and transmits only a modulated wave in a desired frequency band from among the four-phase modulated waves.

[Problem to be solved by the invention]

However, in the conventional PSK modulator described above,
In order to perform modulation using an analog circuit, there is a problem in that it is necessary to adjust the amplitudes of the baseband signals of the (1) channel and Q channel and the phase of the carrier wave.

Therefore, it is an object of the present invention to provide a multilevel multiphase phase modulator that eliminates the need to adjust the amplitude of a baseband signal and the phase of a carrier wave.

Another object of the present invention is to obtain higher modulated waves.

[Means to solve the problem]

Means for solving the above problems are shown in FIGS. 1A and IB.

In FIG. IA, a carrier wave address generator generates an m-bit carrier wave address with a constant sampling period, and a ROM 2 uses an m-bit carrier wave address and a temporally continuous n-bit data sequence as an input address, and The D/A converter 3 outputs a multi-value multi-phase digital modulated wave according to the input address, and D/A converts the multi-value multi-phase digital modulated wave output from the ROM 2. In this ROM2, in advance,
Two orthogonal amplitude commands are calculated from the temporally continuous n-bit data series, each of the two amplitude components is multiplied by a sine wave component and a cosine wave component represented by an m-bit carrier address, and The calculated value obtained by combining the two multiplication results is input using the above-mentioned m-bit carrier wave address and a temporally continuous n-bit data series as input addresses.

In FIG. IB, an impulse generating circuit 4 is further provided which converts the output of the ROM 2 or the output of the D/A converter 3 into an impulse at a sampling period.

[For production]

According to the means shown in FIG. IA, modulated waves are generated or digitally performed, and analog circuits for baseband signal amplitude adjustment and carrier wave phase adjustment are not required.

According to the means shown in FIG. 1B, the frequency distortion of the modulated wave accompanying digital modulation is reduced.

〔Example〕

FIG. 2 is a block circuit diagram showing a first embodiment of a multilevel multiphase phase modulator according to the present invention. In FIG. 2, the serial-to-parallel converter 11 and bandpass filter 23 are the same as those in FIG. The output frequency of this serial-to-parallel converter 11, that is, the symbol data rate fsy* is, for example, I MHz.
It is. Also, 1 is the frequency fe (for example, 2 MHz)
A carrier wave address generation section that generates an address signal Ao''=A2 for generating a carrier wave of the reference oscillator I.
A and a frequency divider IB. The frequency divider IB receives a 3-bit address signal A in order to set the sampling number to 8 (=23), for example. - Send A2. In other words, Ao is alternately "0'" and "1" at frequency 4 fc (= 22 AC).
”, and A is alternately “0” and “1” at frequency 2fc.
Therefore, A2 becomes "0" and ""1" alternately at the frequency fc. In this case, the sampling frequency f, is 4f
It is c.

ROM2 is, for example, an IM with an access time of 100 ns.
It has a byte structure, and its input addresses are a 7-bit data sequence for the ■ channel, a 7-bit data sequence for the Q channel, and a carrier wave address A. , A1, A2, a total of 11 bits are given, and the output is given by 8 pits. That is, the values shown in Table 1 are stored.

Table 1 The results of these two multiplications are combined and stored in each corresponding memory location. To explain more simply, the input data is
■Assuming 1-bit data for the channel and 1-bit data for the Q channel, the calculations shown in Figure 4 are as follows.
That is, the four-phase modulated wave component is (I, Q). The 8-bit data in the ROM 2 is calculated in advance as follows. That is, the amplitude component (synchronous component) is calculated from the 7-bit data sequence of the ■ channel, the amplitude component (orthogonal component) is calculated from the 7-bit data sequence of the Q channel, and then these two orthogonal components are calculated. The amplitude component includes a sine wave component s+n wt and a cosine wave component cos w represented by carrier wave addresses A0, A, .A2 shown in FIG.
Multiply by t, and further. Therefore, in this case, the values shown in Table 2 are stored in ROM2.

Table 2 R OM 2 will be further explained with reference to FIG. 5. In Fig. 2, the symbol ray}f, y
, has the frequency spectrum shown in Figure 5(A) (in case of 100% root roll-off characteristic)
On the other hand, since the carrier wave has a frequency fc, it has a frequency spectrum shown in FIG. 5(B).

In ROM2, the multiplication of the baseband signal having the frequency spectrum shown in FIG. 5(A) and the carrier wave having the frequency spectrum shown in FIG. 5(B) is the convolution integral of these, so ) has the frequency spectrum shown in Furthermore, the digital output of ROM2 is
Frequency 1/f. Since it is a value sampled in FIG. 5(C), the frequency spectrum shown in FIG. 5(C) is convolved with the sampling spectrum, and the digital output value of the ROM 2 has the frequency spectrum shown in FIG. 5(D).

In this way, the modulated wave output having the frequency spectrum shown in FIG. 5(D) is obtained at the output of the ROM 2, that is, the output of the D/A converter 3, so that only the desired frequency components are selected by the bandpass filter 23. It turns out.

However, in reality, in the frequency spectrum shown in FIG. 5(D), the waveform of the ROM 2 output changes stepwise, so the higher the frequency, the more the modulated wave becomes distorted. That is, the frequency spectrum shown in Fig. 6 (B) is applied to the amplitude signal proportional to the digital value having the frequency spectrum (ROM output is impulse-like) shown in Fig. 6 (A) (same as Fig. 5 (D)). The multiplication with the rectangular wave is the convolution of these spectra when expressed on the frequency axis, so the sixth
The result is as shown in Figure (C). As a result, the higher the frequency, the more the modulated wave is attenuated and distorted, making it impossible to obtain a modulated wave of a higher frequency.

By the way, the frequency spectrum shown in FIG. 6(B) is
As shown in FIGS. 7(A) and 7(B), it depends on the sampling period T (=1/f.). In other words, if the sampling period T is made smaller, the frequency spectrum becomes O
It can be seen that the frequency becomes higher.

This trend remains the same even if the sampling period remains constant or the width of each rectangular wave of the sampling waveform is reduced. A second embodiment of the present invention that takes this into account will be described.

FIG. 8 is a block circuit diagram showing a second embodiment of the multiphase phase modulator according to the present invention, in which an impulse generating circuit 4 is added to the components shown in FIG. The impulse circuit 4 includes delay circuits 41 and 42, an exclusive OR circuit 43, and a high-speed switch 44, and has a sampling period of 1/fs, that is, an address A. - The earliest signal A of A2. operates in sync with In addition, the high speed switch 44
is composed of GaAs} transistors, ECL transistors, and the like.

The operation of the impulse generating circuit 4 of FIG. 8 will be explained with reference to the timing diagram of FIG. 9. That is, the output of the D/A converter 3 has a rectangular waveform as shown in FIG. 9(A). On the other hand, the output of the delay circuit 4l is a sampling pulse (not shown) delayed for a certain period of time, as shown in FIG. 9(B), and the output of the delay circuit 42 is as shown in FIG. 9(C). As shown in , this is further delayed for a certain period of time. As a result, the output of the exclusive OR circuit 43 is the sampling pulse A as shown in FIG. 9(D). It becomes a rectangular wave pulse that is synchronized with and has a small width.

The output of this exclusive OR circuit 43 causes the high-speed switch 4
4 is turned on and off, the waveform shown in FIG. 9(D) is changed, and the output of the switch 44 becomes the waveform shown in FIG. 9(E).

The frequency spectrum of the waveform shown in FIG. 9(E) is
As shown in Figure (Δ), as a result, Figure 10 (B)
As shown in , a high frequency band (for example, indicated by X) can be selected as the modulating wave. Note that the arrow Y indicates an appropriate frequency band in the case of the first embodiment in which the impulse generating circuit 4 is not added. (Figure 10 (C) is the same as Figure 6 (C)) In Figure 8, the impulse circuit is connected after the D/A converter 3, but it is connected after the ROM 2. You can.

Furthermore, the ROM2 can have the same function as the ROM2 by adding a digital circuit to the ROMI.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to eliminate the need for adjusting the amplitude of the baseband signal and the phase of the carrier wave in the modulator due to digitization, and the introduction of the impulse circuit makes it possible to output a modulated wave at a high frequency. becomes possible.

[Brief explanation of drawings]

1A and 1B are block circuit diagrams showing the basic structure of the present invention; FIG. 2 is a block circuit diagram showing a first embodiment of the multilevel multiphase phase modulator according to the present invention; FIG. is a carrier wave timing diagram supplementary explanation of the ROM in Fig. 2, Fig. 4 is a circuit diagram explaining the operation of the ROM in Fig. 2, and Figs. 5, 6, and 7 are diagrams of the ROM in Fig. 2. A diagram showing a frequency spectrum for supplementary explanation, FIG. 8 is a block circuit diagram showing a second embodiment of the multilevel multiphase phase modulator according to the present invention, and FIG. 9 is a timing diagram for explaining the circuit operation of FIG. 8. 10 is a diagram showing the frequency spectrum of the modulated wave characteristics of FIG. 8, and FIG. 11 is a block circuit diagram showing a conventional multi-level multiphase phase modulator. 1A...Reference oscillator, IB...Frequency divider, 2-R
OM, 3... D/A converter, 4... Impulse circuit.

Claims (1)

[Claims] 1. A carrier wave address generator (1) that generates m-bit carrier wave addresses (A_0, A_1, A_2, ...A_m) with a constant sampling period; and the m-bit carrier wave address and time. consecutive n
A ROM that takes a data series of bits as an input address and outputs a multivalued polyphase digital modulated wave according to the input address.
(2); and a D/A converter (3) for D/A converting the multivalued multiphase digital modulated wave output of the ROM, Two orthogonal amplitude components were calculated from the bit data series, each of the two amplitude components was multiplied by a sine wave component and a cosine wave component represented by the m-bit carrier address, and the two multiplication results were combined. A multilevel multiphase phase modulator in which a calculated value is stored as the m-bit carrier address and a temporally continuous n-bit data sequence as an input address. 2. Furthermore, the output of the ROM or the output of the D/A converter,
The multilevel multiphase phase modulator according to claim 1, further comprising an impulse generation circuit (4) that generates an impulse at the sampling period.