JPS6357983B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention utilizes a time division communication system and a single channel communication system.
The present invention relates to a transmission output switch used in a Par Carrier, etc., and particularly relates to a modulation circuit that removes unnecessary waves when transmitting or stopping a data signal when the data signal is band-limited in the baseband.

FIG. 1 is a principle diagram of the time division communication system, and FIG. 2 is a time chart of the waveforms of burst signal A and unnecessary wave B for turning on and off switches.

In the figure, 1 is a low-band filter, 2 is a modulator, and 3 is a switch.

In the time-division communication system, the input signal is band-limited by the low-band transmitter 1, modulated by the modulator 2, and the modulated signal is transmitted in the time slot allocated to the own station.
The switch 3 is turned on and off using a burst signal as shown in FIG. However, in this case, as shown in B, unnecessary waves of instantaneous pulses are generated at the leading and trailing edges of the burst signal. In order to prevent this, there is a conventional method described below.

Figure 3 is a time chart of the waveforms, A and E are envelope waveforms of phase modulated waves, B is on/off signal,
C and D are waveforms obtained by turning on and off the waveform of A, and F is an enlarged view of the waveform obtained by turning on and off the waveform of E.

This method utilizes the characteristic that amplitude components are superimposed, such as phase modulation and amplitude modulation, and uses a method in which switching is performed when the amplitude is 0, so that unnecessary waves are not generated. For example, in the case of two-phase phase modulation, if the baseband signal is band-limited by passing it through the low-frequency wave generator 1 as shown in Figure 1, the envelope waveform of the modulated wave becomes a smooth waveform as shown in Figure 3A. . However, if the switch 3 shown in FIG. 1 is turned on and off using the signal shown in B at point A, the rise will become steep as shown in C. For this reason, if the baseband signal is turned on and off in response to the burst signal and the switch 3 shown in FIG. is obtained, and unnecessary waves are no longer generated. This is not a problem in the case of relatively simple modulators such as two-phase modulation circuits, but in 4-phase, 8-phase,...N-phase modulation circuits, due to mismatching of the modulator elements, carrier leakage occurs as shown in Figure 3E. It has the disadvantage that there is no place where it occurs and becomes completely zero.

Figure 4 is a block diagram of a conventional four-phase time division multiplex communication system, Figure 5 is a circuit diagram of a modulator, and Figure 6 is a diagram of the baseband signal voltage and modulated wave in the case of Figure 5. It is a figure showing a phase.

In the figure, 1-1, 1-2 are low frequency devices, 2-1, 2
-2 is a modulator, 4-1 and 4-2 are driver circuits, 5 is a 90 degree phase shifter, and 6 is a hybrid circuit.

In this case, if the modulators 2-1, 2-2 and the hybrid circuit 6 are ideal elements, the input signals are given equal amplitude by the driver circuits 4-1, 4-2, and a perfect 4-channel signal with an offset voltage of 0. It becomes a phase modulated wave, and if the input signal is cut off by switches SW1 and SW2 and the inputs of modulators 2-1 and 2-2 are set to 0, the modulated wave output is switched from 0 as shown in Figure 3D, so it is unnecessary. No waves occur. That is, modulators 2-1, 2-2
The balance mixer used in the system is constructed as shown in FIG. 5, and when the baseband signal input is set to 0 as shown in FIG. 6, the carrier wave and modulated wave are completely separated. However, in reality, due to imperfections in the mixer and other elements such as the hybrid circuit 6, carrier leakage, etc., the modulators 2-1 and 2-2
The amplitude of the signal entering the driver circuit 4-1, 4
-2 offset voltage is shifted and adjusted so that equivalent four-phase modulation is performed by the output of the four-phase modulation circuit. Therefore, switch the baseband signal to SW1 and SW2.
When it is turned on and off, carrier leakage occurs as shown in Figure 3E, and there is no point where it becomes completely zero. Therefore, if the modulated wave shown at E is turned on and off, only the portion aa' corresponding to the carrier leakage responds instantaneously, as shown at F, resulting in the generation of unnecessary waves.

SUMMARY OF THE INVENTION An object of the present invention is to provide a modulation circuit that eliminates unnecessary waves during switching in order to eliminate the above-mentioned drawbacks.

In order to achieve the above object, the present invention switches the input signal of the driver circuit at the front stage of the modulator at a predetermined burst signal length to 0 or a constant voltage at the time of sending and stopping the transmission data burst of the own station, and sets the offset voltage to the data burst. It is characterized in that it is set to a voltage at which the modulated wave has predetermined characteristics at times, and is switched to a voltage at which carrier leakage is zero at times other than data bursts.

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

FIGS. 7 and 8 are principle diagrams of a time division communication system according to an embodiment of the present invention.

In the figure, 7 and 14 are driver circuits, 8 and 15 are low frequency devices, 9 and 16 are modulators, 10 is a switch,
11, 13, 19, and 20 are limiters, 12, 17 are carrier wave oscillators, and 18 is a switch.

The driver circuits 7, 14 switch the input signal by passing it through the limiters 11, 19 at a predetermined burst length, and the driver circuits 7, 14
The offset voltage of the data burst is also changed at other times. That is, the offset voltage is set so that the modulated wave has predetermined characteristics during a data burst, and the offset voltage is set so that the carrier leakage becomes zero when the input signal is stopped. With such a configuration, carrier leakage will not occur when the input signal is stopped, and if the carrier or modulated wave is turned on and off at this point, a burst signal without unnecessary waves as shown in FIG. 3D can be obtained. The difference between FIG. 7 and FIG. 8 is that in FIG.
This is a method in which the entire modulated wave is turned on and off at the 8th
In the figure, the output of the carrier wave oscillator 17 is passed through the limiter 20 in accordance with the burst length, so that the output of the carrier wave oscillator 17 is
This is a method in which the output is turned on and off at the same time, and the same waveform is obtained for both outputs.

Fig. 9 is a circuit diagram of a four-phase modulation circuit mainly including a driver circuit according to an embodiment of the present invention, and Fig. 10 is a circuit diagram when a digital waveform generator is used in front of the driver circuit according to an embodiment of the present invention. , FIG. 11 is a circuit diagram of an embodiment of the present invention in which input signals are turned on and off using a NAND circuit.

In the figure, 21 is a knot circuit, 22 is a driver circuit,
23 and 24 are modulators, 25 is a hybrid circuit, 2
6 is a 90 degree phase shifter, 27 is a carrier wave oscillator, 28 is the same circuit as the circuit having the knot circuit 21, switch SW3 and driver circuit 22, 29 is a shift register, 30 is a NAND circuit, SW3 and SW4 are switches, Va, Vb are offset voltages, R ₁ to _{R 8} ,
R _o is the resistance.

In FIG. 9, when transmitting a burst, the switch SW3 is turned on by the control signal, and the switch SW4 is set to the offset voltage Va side. By adjusting this offset voltage Va, the amplitude of the input signal (baseband signal) is adjusted so that the output of the four-phase modulator (output of the hybrid circuit 25) becomes an ideal modulated wave, and the amplitude of each element is reduced. Correct completeness.

When bursting off, the switch SW3 is turned off and the switch SW4 is set to the offset voltage Vb side. If each element is ideal, when the input signal is 0 and the offset voltage is also 0, the modulated wave output will also be 0. However, carrier leakage occurs due to imperfections in the element, so the offset voltage Vb is adjusted to cancel the phase of the carrier leakage and make the modulated wave output zero.

By doing this, it is possible to obtain a modulated wave that does not generate unnecessary waves, as explained in FIGS. 7 and 8.

That is, by switching the switch 10 in FIG. 7 and the switch 18 in FIG. A burst signal without unnecessary waves as shown in FIG. 3D can be obtained. Furthermore, the low-frequency amplifiers 8 and 1 that should serve as this transfer function
5 is installed after the driver circuits 7 and 14,
The same holds true before the driver circuits 8 and 15 when the system operates linearly. Figure 10 shows the driver circuit 22
A digital wave generator consisting of a shift register 29 is inserted in front of the circuit.If the shift register 29 is reset by a reset signal during burst off, the output becomes a certain constant voltage, and the driver circuit uses this voltage as a reference. If the offset voltage VaVb of 22 is adjusted as described above, the same effect as explained in FIG. 9 can be obtained.

FIG. 11 uses a NAND circuit 30 instead of the switch SW3 in FIG. The offset voltages Va and Vb are
Similar effects can be obtained by making adjustments in the same manner as explained in the figure. By adjusting the offset voltages Va and Vb of the driver circuit 22 in this manner, unnecessary waves can be completely removed. Even when the modulated wave output is in the microwave band, the waveform of the on/off signal can be controlled and shaped by using a pin diode in the switch 10 in Fig. 7 and the switch 18 in Fig. 8, and in particular controlling the current of the pin diode. Since unnecessary waves are not generated even if the device is turned on and off without any need to do so, it can be easily done at low cost.

The above was explained for 2-phase and 4-phase cases, but 8-phase
It can also be applied to multi-phase phase modulation methods such as 16-phase.

As described above in detail, the present invention has the advantage that unnecessary waves can be easily removed at low cost during switching.

[Brief explanation of the drawing]

Figure 1 is a principle diagram of the time division communication system, Figure 2 is a time chart of burst signals and unnecessary waves that turn on and off switches, Figure 3 is a time chart of waveforms, and Figure 4 is a diagram of the conventional four-phase case. A block diagram of the time division multiplex communication system, Figure 5 is a circuit diagram of the modulator,
FIG. 6 is a diagram showing the voltage of the baseband signal and the phase of the modulated wave in the case of FIG. A circuit diagram of a four-phase modulation circuit mainly including a driver circuit according to an embodiment of the present invention, FIG. 10 is a circuit diagram when a digital waveform generator is used in front of the driver circuit according to an embodiment of the present invention, and FIG. 11 1 is a circuit diagram of an embodiment of the present invention in which input signals are turned on and off using a NAND circuit; FIG. In the figure, 1, 8, 15 are low frequency amplifiers, 2, 2-
1, 2-2, 9, 16, 23, 24 are modulators,
3, 10, SW1 to SW4 are switches, 18 is a changeover, 4-1, 4-2, 7, 14, 22 are driver circuits, 6, 25 are hybrid circuits, 5, 26
is a 90° phase shifter, 12, 17, and 27 are carrier wave oscillators,
11, 13, 19, and 20 are limiters, 21 is a knot circuit, 29 is a shift register, 30 is a NAND circuit, R ₁ to R ₈ and _Ro are resistances, and Va and Vb are offset voltages.

Claims (1)

[Claims] 1 In a communication system that performs transmission during the own station's allocated time, when the data signal is band-limited in the baseband, the input signal of the driver circuit in the previous stage of the modulator is cut off or kept constant when transmitting the own station's transmitted data burst and when it is stopped. A modulation circuit characterized in that the offset voltage is variable.