JPH01238346A - Fsk burst transmission spectrum correction circuit - Google Patents

Abstract

PURPOSE:To prevent deviation of a spectrum of modulated wave by devising the circuit such that an alternate signal generated from a clock signal is subject to DC component block by a capacitor and the result is fed to a FSK modulator at the no transmission of a data signal or a burst signal. CONSTITUTION:An alternate signal generator 2 generates an alternate signal repeating codes '0', '1' sequentially from the clock signal. The alternate signal is switched from a signal (data or burst signal) by the control of the transmission switching signal at no transmission by the signal switch 1. The modulation signal (or alternate signal) switched by the switch 1 is subject to band limit by a waveform shaping circuit 3 and the modulation signal whose band is limited is subject to DC component block by the capacitor 5 and the result is fed to a FSK modulator 6. The modulated wave outputted from the FSK modulator 6 is given to a power amplifier 8 through a switch 7 and power-amplified by the said power amplifier 8 to obtain a high frequency output of the modulated wave. Thus, no fluctuation or deviation is caused in the center of the carrier spectrum and modulated wave spectrum outputted from the FSK modulator at transmission and at no transmission.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is an FSK modulation transmitter that transmits a modulated signal by FSK (frequency shift) modulation. This invention relates to a circuit that prevents bias.

(Prior Art) In an FSK modulation transmitter that modulates and transmits a digital signal, when a signal (data signal or burst signal) is not being transmitted, the unmodulated carrier wave output level is suppressed to below a specified value. The input of the FSK modulator output to the power amplifier is cut off. Also, F
When the input end of the modulation signal of the SK modulator and the output end of the pre-stage circuit are directly connected, when the DC component included in the output from the pre-stage circuit fluctuates due to fluctuations in the power supply voltage or ambient temperature. Then, the frequency is shifted directly by the FSK modulator, causing flaws in the spectrum of the modulated wave, and the FSK
Distortion may occur due to departure of the modulation characteristics of the modulator from the linear region. This is true for example in TDMA
In the case of (time division multiple access), it causes interference between adjacent channels and the generation of out-of-band spectrum, which is a serious problem. To this end, a capacitor is used at the input to the FSK modulator to block DC components.

FIG. 2 shows an example of the configuration of a conventional FSK modulation transmitter. 1
° is a signal switcher that switches the signal (data signal or burst signal) and the center voltage of the signal between when transmitting and when not transmitting; 3 is a waveform shaping circuit that limits the band of the digital signal; 4 is a waveform shaping circuit that limits the band of the digital signal; 5 is a capacitor for blocking the DC component of the modulated signal input to the FSK modulator 6; 6 is the FSK modulator with a built-in voltage-controlled oscillator; 7 is the transmitter switching signal. A switch 8 controls to cut off the output of the FSK modulator 6 when the signal is not transmitted, and a power amplifier 8 amplifies the power of the modulated wave to obtain a high frequency output.

When the waveform shaping circuit 3 receives a signal (data signal) as shown in Fig. 3 (a), it limits the band and outputs a rectangular waveform with rounded corners as shown in (b). . The DC component of the output signal is blocked by the capacitor 5, and the FSK
The signal is input to the modulator 6 as a modulation signal. The FSK variant FA
The modulated wave subjected to FSK modulation by the device 6 is inputted to the power/amplifier 8 through the switch 7, and the power is amplified by the power amplifier 8 to obtain a high frequency output of the modulated wave. The switch 7 is controlled by a transmission switching signal, and is turned on when a signal is being sent, and turned off as described above when no signal is being sent. The voltage setter 4 sets the center voltage of the waveform output after band-limiting the signal in the waveform shaping circuit 3, that is, the voltage (Vs++Vs-)/2 shown in FIG. 3(C). When no signal is being transmitted, this voltage is switched by the signal switch 1' under the control of the transmission switching signal described above, and is input as a modulation signal to the FSK modulator 6 through the capacitor 5. FIG. 4(A) shows the relationship between the modulated signal voltage and the output frequency of the modulated wave, and FIG. 4(A) shows the spectrum of the high frequency output.

The reason why the center voltage is supplied to the FSK modulator 6 through the capacitor 5 when no signal is transmitted is because
This is to prevent the carrier wave spectrum appearing at the output of the modulator 6 from being deviated from the center of the modulated wave spectrum at the time of signal transmission.

Suppose that the voltage supplied to the FSK modulator 6 during no transmission is set to the third voltage.
Assuming Vs- as shown in Figure (C), when the state changes from the no-signal transmission state to the signal transmission state and then returns to the no-signal transmission state, the capacitor 5 inserted to block the DC component is Before being sufficiently charged by the signal from the Vs- level, it returns to the Vs- level again. This becomes noticeable when transmitting a burst signal with a short signal length, and as shown in Figure 5, the modulated wave spectrum due to the burst signal is biased from the modulated wave spectrum due to the data signal. arise.

If the capacitance of the capacitor 5 is reduced, the above-mentioned charging will become faster, but in the data signal shown in Figure 3 (a), the length of consecutive parts with the same sign changes significantly. , if its length becomes longer, capacitor 5
The data content of the data signal changes due to the discharge.

Therefore, conventionally, as described above, signal silence (the center voltage set by the voltage setter 4 at 8 o'clock is supplied to the FSK modulator 6 through the capacitor 5 to correct the deviation of the modulated wave spectrum of the burst signal). Was.

(Problem to be Solved by the Invention) However, since the center voltage set by the voltage setting device 4 is DC and is supplied from a DC power supply, it is susceptible to fluctuations in power supply voltage and changes in ambient temperature. , Even if the set center voltage fluctuates and a capacitor is used to block direct current,
The same effect as in the case of supplying the voltage Vs- described above causes the modulated wave spectrum of Burst Toy No. 8 to become biased.

Further, the signal switch 1' uses a semiconductor analog switch from the viewpoint of reliability, but since it is a semiconductor, it is similarly affected by fluctuations in power supply voltage and changes in ambient temperature.
For this purpose, it was necessary to provide a circuit that roughly stabilizes the DC voltage supplied to the voltage setting device 4 and the DC voltage supplied to the semiconductor analog switch used in the signal switch 1''. The variable resistor and semiconductor analog switch used in the setting device 4 needed to be ones whose characteristics did not change much due to ambient temperature.
The drawback was that parts costs were high.

Generally speaking, since the voltage setting device 4 is a regulator, adjustment work is required. The present invention has been made with the aim of eliminating these drawbacks.

(Means for Solving the Problems) The present invention provides an alternating signal generator that generates an alternating signal that sequentially repeats code O and code 1 from a clock signal instead of the above-mentioned center voltage, so that no signal is transmitted. Sometimes a signal switcher changes the signal (data signal or burst signal) to an alternating 48
After switching to the signal and limiting the band using a waveform shaping circuit, the signal is supplied as a modulation signal to the FSK modulator through a capacitor.

(Operation) Since the amplitude of the alternating signal generated by the alternating signal generator is the same as that of the signal, the center voltage of the alternating signal is also the same as the center voltage of the signal. Roughly speaking, since it is an alternating signal in which the same sign does not occur consecutively, there is no fluctuation in the center voltage due to charging and discharging of the capacitor. Therefore, the centers of the carrier wave spectrum and the modulated wave spectrum that can be output from the FSK modulator do not vary between when a signal is transmitted and when a signal is not transmitted. Further, since the alternating number 43 is generated from a clock signal, its center voltage is not affected by fluctuations in power supply voltage or changes in ambient temperature.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention.
1 is a signal switch that switches between a signal and an alternating signal by controlling a transmission switching signal; 2 is an alternating signal generator that generates the alternating signal from a clock signal; and 3 is a signal switch that limits the band of the signal input from the signal switch 1. waveform shaping circuit that outputs
8 is the same component as shown in FIG. 2, and detailed explanation will be omitted.

The alternating signal generator 2 generates an alternating signal that sequentially repeats the code O and the code 1 from the clock signal.

This alternating signal is converted into a signal (data signal or burst signal) by the signal switch 1 under the control of the transmission switching signal when no transmission is being performed.
You can switch from The modulated signal (signal or alternating signal) switched by the signal switch 1 is band-limited by the waveform shaping circuit 3, and the band-limited modulated signal is supplied to the FSK modulator 6 after blocking the direct current component by the capacitor 5. be done. The modulated wave output from the FSK modulator 6 is input to the power amplifier 8 through the switch 7, and is amplified by the power amplifier 8 to obtain a high frequency output of the modulated wave.
The switch 7 is turned on when transmitting a signal (data signal or burst signal), and turned off when not transmitting. The control of the switch 7 is similar to that of the signal switch 1.
This is done by the switch number. FIG. 6 shows the relationship between the output frequency of the FSK modulator 6 and the modulation signal voltage input to the FSK modulator 6. As the modulation signal voltage input to the FSK modulator 6, instead of the data signal or burst signal during transmission, an alternating signal is supplied during non-transmission.
Therefore, the centers of the carrier wave spectrum and the modulated wave spectrum output from the FSK modulator do not fluctuate or become damaged between when transmitting and when not transmitting.

(Effects of the Invention) As explained above, when no data signal or burst signal is transmitted, the AC code 48 generated from the clock signal is supplied to the FSK transformer FJ with the DC component blocked by the capacitor. The center of the carrier wave spectrum and modulated wave spectrum that can be output from the modulator may fluctuate or become biased due to changes in power supply voltage or ambient temperature, or the modulation characteristics of the FSK modulator may “It has the advantage of not causing distortion due to departure from the linearity region. Such an advantage is, for example, TDMA
This is advantageous because problems such as interference between adjacent channels and out-of-band spectrum generation do not occur.

Furthermore, since there is no adjuster such as a variable resistor, there is an advantage that no adjustment work is required.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing an example of the configuration of a conventional FSK modulation transmitter, Fig. 3 (a) is a data signal, and (b) is a waveform shaping output. , (C) are diagrams showing the waveforms of the center voltage, FIG. This figure shows how the modulated wave spectrum is biased by the burst signal, and FIG. 6 is a diagram showing the relationship between the output frequency and the modulated signal voltage according to the present invention. ° 1... Signal switch, 2... Alternate signal generator, 3
...Waveform shaping circuit, 5...Capacitor, 6...
FSK modulator, 7... switch, 8... power amplifier.

Claims (1)

[Claims] A waveform shaping circuit that limits the band of the modulated signal, a capacitor that blocks the DC component of the output signal from the waveform shaping circuit, and a frequency shift (FSK) of the modulated signal with the DC component blocked.
) An FSK modulator that performs modulation, a switch that cuts off the modulated wave output from the FSK modulator under control of a transmission switching signal when no signal (data signal or burst signal) is transmitted, and the modulated wave that is input through the switch. In an FSK modulation transmitter consisting of a power amplifier that amplifies the power of the wave,
an alternating signal generator that generates an alternating signal from a clock signal; and a signal switching device that switches a modulation signal input to the FSK modulator through the capacitor from the signal to the alternating signal under control of the transmission switching signal when the transmission is not performed. An FSK burst transmission spectrum correction circuit, comprising: correcting a bias in a modulated wave transmission spectrum of the burst signal using the alternating signal.