JPH07107130A - Phase modulator - Google Patents

Abstract

PURPOSE:To improve the temperature compensation characteristic by providing a filter having an attenuation characteristic against a double wave in a phase modulation output part of a phase modulating circuit. CONSTITUTION:A carrier wave of a high frequency is bisected by a hybrid circuit 1, and one of them is subjected to pi/2 phase shift and two carrier waves being in an orthogonal relation to each other are obtained. Subsequently, in phase modulating circuits 2, 3, the respective carrier waves are subjected to two phase conversion by digital information of two base bands, and added and synthesized by a hybrid circuit 4. In this case, as to the phase modulating circuits 2, 3, a balance modulating circuit using a diode is used, and a filter (a filter of band pass and low pass, etc.) having an attenuation characteristic against a double wave is connected to its output terminal. That is, a stub 5 whose one end is connected to a modulation output is provided, and between its other end and a ground (reference point), a parallel connecting circuit of a capacitor 6 and a resistance 7 is provided. As for the stub 5, length of that of lambda/4 against wavelength lambda of a fundamental wave is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase modulator, and more particularly to a phase modulator in a microwave band radio communication device.

[0002]

2. Description of the Related Art An example of a conventional phase modulator of this kind is described in "Basics of Digital Modulation / Demodulation Circuits" by Seizo Seki, published by Ohmsha Co., Ltd. in p.
There is a 4-phase PSK phase modulation circuit disclosed in 65-67.

In this type of phase modulator, it is necessary to perform temperature compensation in order to improve the temperature characteristics, but this temperature compensation is not performed by the phase modulator itself, but a baseband that gives a modulation signal to the phase modulator. In the circuit, temperature compensation is performed on the voltage amplitude of the modulation signal.

[0004]

In the conventional technique of this type, the baseband circuit for supplying the modulation signal to the phase modulation circuit performs temperature compensation of the voltage amplitude of the modulation signal, and the amplitude of each phase at the time of phase modulation. Is made constant and the phase difference of each phase is made constant, thereby operating the phase modulator.

However, in this method, it is a condition that all the same currents flow by applying the same voltage to all the diodes of each phase of the balanced modulator itself constituting the phase modulator.

Further, since the phase modulator uses the carrier signal saturated for the purpose of stabilizing the output level, the phase modulator operates similarly to the frequency multiplier, and the second harmonic (2 The second harmonic is generated, and thus the fundamental wave and the second harmonic are generated by the modulator. The attenuator and amplifier connected to the next stage are designed to have an appropriate impedance for the fundamental wave, but considering the impedance for the second harmonic is effective for high frequencies. The circuit element is selected and used, which is not suitable in terms of cost.

Therefore, if a design is made at a low cost while sacrificing the consideration of the impedance for the second harmonic, the second harmonic output from the phase modulator is reflected by the input unit of the attenuator or amplifier at the next stage to perform phase modulation. Then, the adjustment is performed in a state where an excessive bias current is supplied to each diode of each phase of the phase modulator itself.

When the temperature changes in such a state, the output level of the second harmonic wave generated by the modulator changes,
The extra bias current given to the diode of the modulator also changes due to the reflection of the second harmonic, so that the operating point of the diode changes and the characteristics of the phase modulator cannot be maintained.

Further, considering the impedance with respect to the second harmonic wave, it is necessary to use a component effective at a high frequency. To be more specific, if it is an attenuator, it must be smaller and have a large amount of attenuation that can sufficiently absorb the reflection of the amplifier in the next stage. Both the characteristics and the isolation characteristics are good, and a circuit having a high intercept point is required, which is extremely disadvantageous in terms of cost.

Therefore, the present invention has been made to eliminate the drawbacks of the prior art, and its purpose is to eliminate the influence of the second harmonic generated by the phase modulator itself at low cost. Another object of the present invention is to provide a phase modulator that can achieve good temperature compensation.

[0011]

A phase modulator according to the present invention comprises a phase modulation means for phase-modulating a predetermined carrier wave by digital information, and a frequency signal component of the phase-modulated output which is twice the frequency of the carrier wave selectively. And a filter means for attenuating.

[0012]

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

FIG. 1 is a circuit diagram of an embodiment of the present invention. In the figure, 4 shown in the prior art document mentioned above is shown.
The circuit diagram at the time of applying this invention to a phase PSK phase modulator is shown.

In this circuit, a high frequency carrier wave is divided into two by the hybrid circuit 1, and one of them is phase-shifted by π / 2 to obtain two carrier waves which are orthogonal to each other. Then, in the phase modulation circuits 2 and 3, each carrier wave is subjected to two-phase phase modulation using two pieces of baseband digital information, and the hybrid circuit 4 performs addition and synthesis.

A well-known balanced modulation circuit using a diode is used for the phase modulation circuits 2 and 3, and as described above, if no action is taken on the second harmonic wave at the modulation output section, the diode is used. Bias current fluctuates due to temperature changes, and the temperature characteristics of the modulation circuit deteriorate.

Therefore, in this embodiment, a filter (a bandpass filter, a lowpass filter, etc.) having an attenuation characteristic for the second harmonic wave is connected to the output terminal. That is, the stub 5 having one end connected to the modulation output is provided, and the parallel connection circuit of the capacitor 6 and the resistor 7 is provided between the other end and the ground (reference point). In this case, the stub 5 has a length of λ / 4 with respect to the wavelength λ of the fundamental wave.

In such a configuration, before applying the configuration of the present invention, a phase deviation of about 30 ° was generated in the range of -10 ° C to + 70 ° C, but in the configuration of FIG. The change made it possible to accommodate a phase deviation of about 5 ° (1/6).

[0018]

As described above, according to the present invention, since the phase modulation output section is provided with the filter having the simple attenuation characteristic for the second harmonic wave, the temperature compensation characteristic becomes extremely excellent. effective.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

[Explanation of symbols]

 1,4 Hybrid circuit 2,3 Phase modulation circuit 5 Stub 6 Capacitor 7 Resistance

Claims (2)

[Claims] 1. A phase modulation means for phase-modulating a predetermined carrier wave by digital information, and a filter means for selectively attenuating a frequency signal component of the phase-modulated output which is twice the frequency of the carrier wave. Phase modulator. 2. The filter means is connected between an output of the modulation means and one end of which is a stub having a length of λ / 4 of the fundamental wave of the carrier wave, and the other end of the stub and a reference potential point. 2. The phase modulator according to claim 1, wherein the phase modulator comprises a parallel circuit of a resistor and a capacitor connected to each other.