JPS6357982B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to switching of transmission output used in time division communication systems, single channel per carrier (SCPC), etc., and particularly when data signals are band-limited in the base band. The present invention relates to a modulator that removes unnecessary waves caused by burst signals by adding a specific bit and changing the offset voltage of a modulator driver.

In the time-division communication system, the signal is transmitted during the allocated time period of the own station, so the modulated output is switched by the burst signal of the own station, as shown in FIG. 1, and the signal is transmitted during the allocated time period of the own station.

However, since it is turned on and off by a switch, unnecessary waves are generated by the instantaneous pulses shown in b at the leading and trailing edges of a in Fig. 2.

In order to prevent the generation of unnecessary waves, transmission systems that utilize the amplitude characteristics of signals have been proposed.

In other words, it takes advantage of the characteristic that amplitude components are superimposed on signals such as phase modulation and amplitude modulation, and adds specific bits to prevent instantaneous unnecessary waves from being generated by switching even when using a simple switch. be.

For example, to explain two-phase modulation, as shown in Figure 1, the baseband signal is band-limited in advance using a low pass filter 1 (LPF).
In the IF or RF band, the modulated signal is subject to a narrow band limit even if the transmission path is not band limited.

The amplitude characteristics waveform-shaped in this way are used as they are as the transient characteristics of the switch.

However, when the signal in Figure 3 a is turned on at position b,
If it is turned OFF, the output will have a steep rise as shown in c in the same figure, so to obtain a waveform like e,
The burst position must be set to point d.

Therefore, as shown in FIG. 7, the same inventor has already proposed a method of adding 2 bits or several bits before and after the burst length of the own station so as to always cause a change of π/0 or 0/π like c.

Here, the burst signal is input at the position shown in Figure 7 d.
By turning ON/OFF, a modulated burst signal as shown in Fig. 3e can be obtained, and no unnecessary waves are generated. However, this is not a problem in the case of relatively simple modulators such as two-phase modulators, but with four-phase, eight-phase... n-phase modulators, due to mismatching of the constituent elements themselves, the best band system alone cannot achieve a perfect 100 % amplitude modulation will not occur and carrier leakage will occur. For example, in the case of four phases, if the modulators 6 and 7 and the hybrid 9 in FIG. 4 are ideal elements, the PN signals I and Q are set to a in FIG. A complete four-phase modulated wave can be obtained as shown below.

That is, since complete π/0, 0/π modulation is achieved here, the modulated wave output is switched from zero as shown in FIG. 4a, and no unnecessary waves are generated.

However, in reality, the balance mixer used in the modulators 6 and 7 is configured as shown in Figure 8.
It is used as a π modulator. Also, due to imperfections in hybrids and carrier delays, the amplitude and offset voltage of the modulated wave are intentionally shifted to ensure equivalent four-phase modulation with the output of the four-phase modulator. .

Therefore, the output is not 100% amplitude modulated as shown in FIG. 5b, and carrier leakage often occurs. Then, by turning the modulation wave ON/OFF, the fifth
As shown in c in the figure, only part aa responds instantaneously.
Therefore, unnecessary waves due to the above-mentioned burst signal are generated.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, an object of the present invention is to provide a modulation circuit that can completely reduce the amplitude of a modulated wave to zero when a burst signal is turned ON/OFF, thereby preventing the generation of unnecessary waves. There is.

Further, an object of the present invention is to transmit data transmitted from the own station in a time-division call in which transmission is performed during the allocated time of the own station.
means for adding specific bits before and after the burst;
This is achieved by a modulation circuit characterized by comprising means for changing the offset voltage only before and after the data burst, and causing the amplitude of the data transmitted by the local station to cross zero when transmitting the data bust ON/OFF signal. Ru.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 6 shows the configuration of the present invention.

Here, a specific signal with two or more bits added before and after the burst is band-limited by an LPF, then modulated and switched at a predetermined burst length. Here, the controller 14 switches the driver circuit 10 during additional bits or times other than burst data. In other words, during data, the DC bias voltage is adjusted so that the modulated wave has the specified characteristics.
The modulator 12 is configured so that the amplitude of the modulated wave crosses zero only during the time when the additional bits π/0 and 0/π are included.
The input offset voltage is intentionally shifted.

With such a configuration, the modulated wave during ON/OFF always crosses zero, so if the burst ON/OFF signal is transferred from the controller 15 at this point, unnecessary waves will not occur as shown in Figure 5a. You can get burst signals.

FIG. 9 shows a specific example of the circuit of the present invention, and its operation will be explained below using FIG. 10 showing its output signals.

The offset voltage in FIG. 9 is set to Va at the time of data, and at this point, the balance mixer AV1 is used to adjust the amplitude of the burst hand signal to correct imperfections in each element and obtain a modulated signal.

Then the switching time, for example π/0 as shown in Figure 10c.
Alternatively, switch SW is switched to Vb and Vb is adjusted so that the 0/π modulated wave always crosses zero.

At this time, as shown in FIG. 10b, the amplitude component becomes unbalanced due to the phase, amplitude, etc. of the modulated wave, but this bit can be ignored because it can be regarded as a card bit.

Then, the controller 15 shown in FIG.
If you switch at the position d in Figure 0, it will start from zero as shown in e.
Since it is switched according to the transfer function of the LPF 11, no unnecessary waves are generated.

As described above, according to the present invention, unnecessary waves caused by switching can be completely removed by controlling the offset voltage of the modulator for several bits before and after the switching point.

In addition, the switch in the microwave band can be turned on/off 100% using a pin diode, just like in the past. That is, sufficient effects can be obtained in terms of cost and difficulty without controlling the current of the pin diode and shaping the waveform of the ON/OFF signal.

Note that although the present invention has been explained in the case of two phases, there are also four phases.
It can also be applied to modulation circuits such as multi-phase phase modulation and amplitude modulation such as phase modulation and 8-phase modulation.

[Brief explanation of drawings]

Figures 1 and 4 show conventional modulation circuits, Figure 2,
Figures 3 and 5 show each signal during a conventional data bust, Figure 8 shows a balance mixer, Figure 6,
FIG. 9 shows an embodiment of the present invention, and FIGS. 7 and 10 show respective signals at the time of data burst in the present invention. In the figure, 1, 5, 11 are LPF, 2, 6, 7,
12 is a modulator, 3, 13 is a switch, 4, 10
indicates a driver, 9 indicates a hybrid, 8 indicates a phase shifter, 14 and 15 indicate a controller, and AV1 indicates a balance mixer.

Claims (1)

[Claims] 1. In a time-division call in which transmission is performed during the allocated time of the own station, the transmitter is equipped with means for adding specific bits before and after the data burst transmitted by the own station, and means for changing an offset voltage only before and after the data burst, A modulation circuit characterized by zero-crossing the amplitude of local station transmission data during data burst ON/OFF signal transfer.