JPS60219856A - Demodulation circuit for digital modulation wave - Google Patents

Abstract

PURPOSE:To simplify the constitution by constituting the titled circuit with a phase detector comprising an amplitude limit circuit, a frequency detector and an integration device and with a decider deciding an output of the phase detector in response to a prescribed phase. CONSTITUTION:A digital modulation wave signal received by a reception antenna 710 is inputted to the phase detector 745 via the amplitude limit circuit 730. The phase detector 745 consists of the frequency detector 740 inputting an output of the amplitude limit circuit 730 and detecting the frequency and of the integration circuit 750 integrating the output by a repetitive period of a transmission digital signal. An output of the phase detector 745 is inputted to a deciding circuit 760 and the deciding circuit 70 decides an output proportional to the phase of the phase detector 745 according to the phase to modulus 2pi.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a digitally modulated wave demodulating circuit having a simple circuit configuration for demodulating a received signal modulated by a digital signal.

(Prior art and its problems) Among the technical issues in digital communication, modulation and demodulation technology is very important in wireless communication.

In particular, among the modulation and demodulation characteristics, the transmission spectrum and power utilization efficiency are important on the transmission (modulation) side, and the error rate characteristics are important on the reception (demodulation) side. In addition, the feasibility of transmitter and receiver circuits is also a major practical issue. Among these, the linear modulation method, in which the band is determined in principle only by a band-limiting filter in the baseband l, is the most superior in terms of the transmission spectrum. Conventionally, linear modulation methods, such as microwave multiplex communication, are somewhat difficult to implement in circuits and are expensive overall, but because multiplexing is performed, the price per channel is not much of a problem. Such systems have been adopted. However,
Usually, in a one-channel D system such as in mobile communication, an increase in cost due to the difficulty in realizing the circuit is a major problem. In particular, in mobile communications, in addition to the feasibility of using one transmission circuit, the receiving power fluctuates by, for example, 80 dB, so an automatic gain control circuit with a large dynamic range is required on the receiving side. In addition, since the demodulation method requires a complex circuit configuration such as synchronous detection, the linear modulation method has not been used so far.

In fact, this article was adopted, for example, by Hirata et al., in the February 1980 issue of the Journal of the Institute of Electronics and Communication Engineers, pages 192 to 198, entitled ``Digital Transmission Technology for Mobile Communications.'' Among the technology outlook articles published in
Since the band of the baseband signal also depends on the modulation index l, it is inevitable that the frequency band will be wider than in the linear modulation method.

(Object of the Invention) An object of the present invention is to provide a demodulation circuit with a simple receiving circuit configuration in order to realize a linear modulation method in mobile communication.

(Structure of the Invention) According to the present invention, a digital modulation wave demodulation circuit demodulates a linear modulation wave that has been modulated to take a predetermined phase point corresponding to a digital signal to be transmitted. ,
A phase detector that performs phase detection of the linearly modulated wave, the amplitude limiting circuit receiving the linearly modulated wave as an input, the amplitude limiting circuit, and a frequency detector performing frequency detection using the output of the amplitude limiting circuit as an input. a phase detector consisting of an integrator that uses the output of the frequency detector as input and divides the repetition period of the transmitted digital signal; and a determiner that uses the output of the phase detector as input to determine the digital signal. There it is,
A demodulating circuit for digitally modulated waves is obtained, which includes a determiner that determines the output proportional to the phase of the phase detector in correspondence with the phase modulo 2π.

(Example) The present invention is as described above! Among NIhy, the amplitude limiting circuit can cope with large fluctuations in the input power with a simple circuit. Furthermore, by using a frequency detector as a wave detector, detection (b) can be easily realized. Furthermore, by performing signal determination in accordance with the phase modulo 2π, the deterioration of error rate characteristics caused by the IC due to the use of a frequency detector is improved.

Embodiments of the present invention will be described in detail below with reference to the drawings.
I will explain this. FIG. 1 shows a professional diagram of a modulator that generates a first example of a linearly modulated wave that is the target of the demodulator of the present invention, and FIG. 2 shows the phase point and frequency of the modulated wave in this case. The signal trace is shown on the complex amplitude plane. A digital signal to be transmitted is inputted from input terminals 111 and 112 and inputted to low-pass filters 121 and 122. The output signals of the low-pass filters 121 and 122 are input to mixers 131 and 132, respectively, and the locally generated signal input at the same time is modulated in amplitude by f. The local oscillation signal is obtained by inputting the output of the local oscillator 140 to a 90° phase difference separation circuit, and the phases between the two local oscillation signals differ by 90°. Mixa 131, 13
The output of 2 is inputted to the adder circuit 160, and then outputted to the output terminal 170 and sent to the output terminal 170. Strange things like this *
'a is well known as a quadrature modulator. This modulator uses the baseband (
It is a linear modulator because it is a signal obtained by converting the frequency of signal g by one carrier wave band. Therefore, in principle, the transmission spectrum is determined only by a low-pass filter, and the spectral band can be narrowed.On the other hand, in nonlinear modulation methods such as frequency modulation, the spectrum is determined by the modulation index as well as the baseband signal spectrum. Therefore, it is inevitable that the spectrum band will be wider than that of the linear modulation method.

The phase points of the modulated signal are the points indicated by the Ω mark and the N mark in FIG. Here, depending on the binary signal input to the input terminal 111, one of the phases indicated by the N mark is input to the input terminal 111.
Depending on the binary signal input to 12, one of the phases indicated by the Q mark is selected. Here, by shifting the timings of the two digital signals, the phase points indicated by the 0 mark and the N mark are alternately taken. This t signal trajectory is troubling as roughly indicated by the straight line in the same figure. Such a modulation method is known as π/2 shift 1-B)'SK.

FIG. 3 is a block diagram of a modulator that generates a second example of a linearly modulated wave to which the present invention is applied. A pair of binary digital signals inputted simultaneously to input terminals 311 and 312 are passed through a pair of low-pass filters 321 and 322 and a pair of low-pass filters 323 and 324 by a switch circuit 320.
! l# are input alternately. Low pass filter 321
, 322, 323, and 324 are input to mixers 331, 332, 333, and 334, respectively, to amplitude-modulate the simultaneously input local oscillation signals. The local oscillation signal is obtained from the output of the local oscillator 340 as the output of the phase difference separation circuit of 0°, 90°, 45°, and 135°. The f-tone signal is input to the adder circuit 360 and then output to the output terminal 370.

In this case as well, since a linearly modulated wave is obtained in the same way as shown in FIG. 1, the band of the transmission spectrum is narrow.

Figure 2F\4 is a complex amplitude plan view showing signal points and loci in this case. The point marked with p is mixer 333,
The point marked N is given by the set of mixers 331 and 332.

Since the two sets of alternating mixers are selected by the switch circuit, the signal trajectory is approximately as shown by the straight line in the same figure. Which of the four signal points D-inkata and flash is selected is determined by the combination of two binary signals. Such a modulation method is well known as "/4 shift QPSK."

FIG. 7 is a block diagram showing an example of the configuration of a receiver using the helium adjuster of the present invention. The linear harmonics received by input antenna 710 are band-limited by bandpass filter 720 and then input to amplitude limiting circuit 730 . The amplitude limiting circuit may be one used in conventional mobile radio equipment for frequency modulated waves. Even if an automatic gain control circuit is used instead of the amplitude limiting circuit, the same effect can be obtained in principle, but as mentioned above, the circuit configuration inevitably becomes complicated. The signal is input to a phase detector 745. Frequency detectors may also be those used in conventional mobile radio equipment. It is a well-known fact that the frequency detector is six times easier to construct than, for example, a synchronous detector. The principle of phase detection in the present invention will be explained using the complex amplitude plan view shown in FIG. 5 and the @harmonic waveform diagram shown in FIG. Here, we will consider the case of shift 13P8, and consider the case where the signal point changes from A to B in Figure 5. When there is no noise, the signal trajectory of the input modulated wave 11 points A to point B
It becomes a trajectory a that goes directly on the bulge. By inputting this signal to the amplitude limiting circuit 730, the output signal trajectory becomes trajectory #b on the circumference. The frequency detector 740 outputs an instantaneous angular frequency that is the rate of change of the phase angle with respect to the origin 0 of the trajectory. The output is input to an integral discharge circuit 750 and integrated. Therefore, the output of the integral discharge circuit 750 has a phase difference from the signal point A to the signal point B, that is, "/2" in this case.
A circuit 745 in which 0 and the integral discharge circuit 750 are connected forms a phase detection circuit. If the signal point A changes to 0, the output of the phase detection circuit 745 will be as follows, in the same way as before.
A phase difference of /2 is obtained. Therefore, the 2 to send
Depending on the value signal, the phase change is f/ or -”/2
If the modulation is performed so that ξ, the output of the phase detector becomes
By making the determination at 70, transmission data is obtained at the output terminal 780.

FIG. 6 is a diagram for explaining the operation of determining the output of the phase detector. Integrating discharge filter 750 starts integrating from symbol time t1, and the next symbol time t! after symbol period T! A phase change of "now or -"/2 is obtained. Judging the output of C with the judgment error being 0.
Transmission data is thus obtained. Here, the timing of the integral discharge filter and the timing of determination are given by the clock extraction circuit 770. Similarly for the signal point arrangement as shown in FIG. 4, transmission data can be obtained by setting three determination levels.

The above explanation assumes that noise is ignored; however, in reality, noise cannot be avoided. The explanation will be given by returning to FIG. 5 again. When the signal point of transmission changes from A to B, the noise causes the bandpass filter 720
For example, the trajectory of the output may be as shown in C. At this time, the output of the amplitude limiting circuit 730 becomes as shown by the locus d, and the output signal of the integral discharge filter 750 becomes as shown by the broken line in FIG.

In this case, even if the end point of the trajectory is the correct point B, the error rate is improved by adding the error as long as the determination level is set to 0.

This is to consider phase detection output signals obtained by rotating clockwise and counterclockwise with respect to the end point of the same signal trajectory as the same signal point. In other words, the phase change is 2
The determination is made using π as the modulus. In the previous example, the regions R1 and R3 shown in FIG. Since the phase points falling in the region of approximately 4 are determined as the same signal point, even when the signal trajectory is C, the determination will be made correctly. Regarding the signal point arrangement as shown in FIG. 4, the decision error rate can be improved in the same manner.

(Effects of the Invention) As already mentioned, the present invention has the effect of simplifying the demodulation circuit because the amplitude limiting circuit and the frequency detection circuit can be used. Furthermore, as an effect of the decision circuit of the present invention that makes decisions modulo 2π, for example, when the signal point arrangement is as shown in FIG. (It was found that an improvement of 3 dB can be obtained by converting the ratio f of carrier power to noise power, which is r3.

[Brief explanation of drawings]

1 and 3 are diagrams respectively showing first and second configuration examples of a modulator that generates a linearly modulated wave targeted by the demodulation circuit of the present invention, and FIGS. FIG. 5 is a complex amplitude plan view showing signal points and trajectories of the modulator shown in FIGS. A diagram showing an example of a signal waveform for explaining the operation of the circuit, and FIG. 7 is a block diagram showing an example configuration of a receiver using the demodulation circuit of the present invention. In these figures, 121 , 122 , 321 ,
322323, 324 are low pass filters, 131
, 132.331332, 333, 334 are mixers, 160, 360 are adder circuits, 140, 340 are local oscillators, 145, 345 are phase difference separation circuits, 320
is a switch circuit, 710 is a receiving antenna, 720 is a band pass filter, 730 is an amplitude limiting circuit, 740 is a frequency detector, 745 is a phase detector, 750 is an integral discharge filter, 760 is a determination circuit, 770 is a clock regeneration circuit, 7
80 is the judgment output signal output terminal 1 and a half times 3 Figure & σ 〃θ

Claims (1)

[Claims] Corresponding to the digital signal to be transmitted, a digital modulated wave transposing circuit demodulates a linearly modulated wave modulated to take a predetermined phase point. A phase detector that performs phase detection on a linearly modulated wave, comprising an amplitude limiting circuit that receives the linearly modulated wave as an input, a frequency detector that performs frequency detection using the output of the amplitude limiting circuit as an input, and an output of the frequency detector. and an integrator that integrates the transmission digital signal over the repetition period of the transmitted digital signal; and a determiner that determines the digital signal by inputting the output of the phase detector, the phase detector comprising: 1. A demodulation circuit for a digital modulated wave, comprising a determiner that determines an output proportional to l in correspondence with a phase modulo 2π.