JPS60247309A - Instantaneous deviation control circuit - Google Patents

Abstract

PURPOSE:To improve the distortion characteristics by adding a phase shift circuit between an amplitude limiting circuit and a modulator for compensation of the phase characteristics obtained by an LPF. CONSTITUTION:When a high level is supplied to a signal input terminal C, an input signal receives the limitation of amplitude through an amplitude limiting circuit 4. Thus many higher harmonic waves are produced. The frequency components outside the band of a transmitter are removed out of the higher harmonic waves through an LPF5. While the frequency components within the band of the transmitter are delivered through the LPF5 with the phase different from the input signal component owing to the phase characteristics of the LPF5. A phase shift circuit 6 compensates the different phase relations to approximate the input signal component to the higher harmonic wave component within the band. Therefore it is avoided that the voltage of a signal supplied to a modulator 7 is increased unnecessarily.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an instantaneous deviation control circuit for a modulation circuit comprising an amplitude limiting circuit and a low-pass filter modulator.

(Prior Art) In the conventional instantaneous shift control circuit shown in FIG. 2, when the signal applied from the A terminal is excessive, the amplitude is limited by the amplitude limiting circuit l. Since the output of the amplitude limiting circuit l contains harmonic components due to amplitude limiting, the low pass filter 2
This eliminates harmonic components and prevents the frequency spectrum outside the communication band from spreading.

However, due to the phase characteristics of the low-pass filter, the output signal of the low-pass filter is such that the peak voltage of the fundamental wave component of the signal and the harmonic component caused by the amplitude limit are close in time, and the peak value of the input signal to the modulator is It gets bigger.

FIG. 3 is a graph showing the modulator input waveform when an excessive input is applied to the A terminal using the circuit configuration shown in FIG. 2, using a filter that passes frequency components within the speech band.

At this time, the frequency deviation with respect to the input signal level to the human end is shown in a graph without a phase shift circuit in FIG.

From these graphs, it can be seen that with this circuit configuration, the effect of suppressing the frequency deviation to below a certain level with respect to an excessive input signal is large. For this reason, a method has conventionally been adopted in which the modulation sensitivity of the modulator 3 is reduced in order to keep the firing deviation of this frequency below a specified value. However, in this method, in order to obtain a standard frequency shift, it is necessary to increase the signal level applied to the A terminal by an amount corresponding to the decrease in the sensitivity of the modulator, and the problem remains that distortion due to the amplitude limiting circuit increases.

(Object of the Invention) The object of the present invention is to solve the above-mentioned drawbacks by adding a phase shift circuit that compensates for the phase characteristics caused by the low-pass filter between the amplitude limiting circuit and the modulator, and to improve the distortion characteristics. The purpose is to provide a transmitter.

(Structure of the Invention) In order to achieve the above object, an instantaneous deviation control circuit according to the present invention includes a modulation circuit including an amplitude limiting circuit, a low-pass filter, and a modulator, and includes a modulating circuit including an amplitude limiting circuit and a modulator. It is constructed by inserting a phase shift circuit into the

(Example) The present invention will be described in more detail below with reference to the drawings and the like. FIG. 1 is a block diagram showing a sixteenth embodiment of an instantaneous deviation control circuit according to the present invention. - This embodiment includes an amplitude limiting circuit 4 connected to the signal input terminal O, a low-pass filter 5 connected to the amplitude limiting circuit 4, a phase-shifting circuit 6 connected to the low-pass filter 5, and a phase-shifting circuit 6 connected to the phase-shifting circuit 6. Modulator 7
It is composed of Rikita and others.

If the signal input terminal O is now at a high level, the amplitude limiting circuit 4
Therefore, the input signal is limited in amplitude.

As a result, many harmonics are generated. Among these harmonics, frequency components outside the transmitter band are dropped by the low-pass filter 5. However, due to the phase characteristics of the low-pass filter 5, the frequency components within the band are outputted from the low-pass filter with a phase different from that of the input signal component.

The phase shift circuit 6 compensates for this different phase relationship and brings the input signal component and the in-band harmonic component closer in phase. Therefore, the voltage of the signal entering the modulator 7 will not become unnecessarily high.
.

The output of the phase shift circuit 6 is frequency modulated by a modulator 7.

FIG. 4 shows the output of the phase shift circuit 6. The peak value of the signal voltage is lower than when the phase shift circuit 6 is turned off. The graph of FIG. 5 with the phase shift circuit shows the relationship between the input signal level and frequency deviation in the circuit configuration of FIG. 1. Since the voltage of the signal entering the modulator 7 is lowered by the phase shift circuit 6, the frequency deviation is small. A similar effect can be obtained by inserting it between the limiting circuit and the low-pass filter. FIG. 6 shows a block diagram of another embodiment. In the embodiment shown in FIG. 6, the output of the amplitude limiting circuit 8 is connected to a phase shift circuit 9, and the output of the phase shift circuit 9 is connected to a low pass filter 10.

The output of the low-pass filter lO is connected to a modulator 11.

FIG. 7 is a circuit diagram showing an embodiment in which the phase shift circuit is composed of a differential amplifier. The constants of the resistor 14 and capacitor 15 are determined according to the phase characteristics of the low-pass filter 5 and IO.

By adding a phase shift circuit to the instantaneous shift control circuit as in this embodiment, it is possible to prevent the maximum value of the input signal voltage to the modulator for a high b level input signal from becoming unnecessarily high. therefore.

Modulator sensitivity can be set high. As a result, the standard signal level of the amplitude limiting circuit becomes lower, and the distortion can be reduced because the amplitude limiting circuit can be used in a highly linear region of the output characteristics.

(Effects of the Invention) As described above, in the present invention, by adding a phase shift circuit to the instantaneous shift control circuit of the transmitter, it is possible to obtain the effect of improving the distortion characteristics of the transmitter.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an instantaneous shift control circuit showing an embodiment of the present invention. FIG. 2 is a block diagram of a conventional instantaneous deviation control circuit. Figure 3 is a graph showing the Kugata signal waveform (solid line), its fundamental wave component, and third harmonic component (broken M) to the modulator when a high b level is input to the input end of the circuit in Figure 2. It is. FIG. 4 is a graph showing the waveform of the input signal to the modulator (solid line) and its fundamental wave component and third harmonic component (broken line) when a high level is input to the C end of FIG. FIG. 5 is a graph showing the frequency shift of the signals at the B and C terminals with respect to the signal levels applied to the An/A and C terminals in the circuits of FIGS. 2 and 1. FIG. 6 is a block diagram showing a second embodiment of the instantaneous deviation control circuit according to the present invention. FIG. 7 is a circuit diagram showing an embodiment of the phase shift circuit. 1... Amplitude limiting circuit 2... Low pass filter 3.
...Modulator 4...Amplitude limiting circuit 5...Low pass filter 6...Phase shift circuit 7...Modulator 8...Amplitude limit circuit 9...Phase shift circuit 10... Low-pass filter 11...Modulator 12.13.14...Resistor 1
5...Capacitor 16...Differential amplifier A...Signal input terminal B...Modulator output terminal 0...Signal input terminal
D...Modulator output end E...Signal input end F...Modulator output end G...Phase shift circuit input end H...Phase shift circuit output end Patent applicant NEC Corporation Agent Patent Attorney Hisashi Inoro Figure 1 Figure 2a Figure 3 Figure 4

Claims (2)

[Claims] (1) An instantaneous shift control circuit characterized in that the modulation circuit includes an amplitude limiting circuit, a low-pass filter, and a modulator, and a phase shift circuit is inserted between the amplitude limiting circuit and the modulator. (2) The instantaneous shift control circuit according to claim 1, wherein the phase shift circuit is constructed using a differential amplifier.