JPH0691372B2 - Modulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a modulator for changing a carrier wave on the transmission side according to a signal wave.

[Conventional technology]

Conventionally, in a modulator using a PLL (Phase-Locked-Loop), (1) the reference oscillator is directly modulated.

(2) The voltage controlled oscillator is directly modulated.

(3) A modulator is separately provided, and a desired frequency is obtained by frequency mixing with a local oscillator.

And so on.

[Problems to be solved by the invention]

However, in the above method (1), since the reference oscillator itself is modulated, it is difficult to increase the stability of the reference oscillator, and a reference oscillator is required for each modulator, resulting in an uneconomical system.

Further, in the above method (2), when the modulation frequency is low, it is necessary to lower the band of the low-pass filter inserted between the phase comparator and the modulator. Therefore, it takes time to change the carrier frequency of the modulator. There is a drawback that ends up.

The above method (3) can improve the stability of the reference oscillator, which is a disadvantage of the method (1), and has a modulator separately, which is a drawback of the method (2). Even if the frequency is changed, the frequency can be changed quickly by changing the frequency of the local oscillator, but the circuit becomes complicated and expensive due to the mixer, bandpass filter, and amplifier.
Moreover, since a mixer is used, it may cause spurious emission.

It is an object of the present invention to provide a modulator characterized by high frequency stability, stable modulation until the modulation frequency is reduced, and the frequency of the modulator being switched quickly.

[Means for solving problems]

A modulator according to the present invention includes a reference oscillator and a first frequency variable oscillator for inputting a signal wave for modulation, and a first frequency variable oscillator that does not follow the signal wave and is phase-locked with the output of the reference oscillator. Second phase synchronizing means having a phase synchronizing means and a second frequency variable oscillator for carrier wave, and performing phase synchronization by following the output modulated by the signal wave from the first frequency variable oscillator Therefore, when an AC signal wave is applied to the modulation terminal of the first frequency variable oscillator,
The second variable frequency oscillator can be modulated.

〔Example〕

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

FIG. 1 is a block diagram showing an embodiment of the modulator according to the present invention. The first variable frequency oscillator 4 is composed of a voltage controlled oscillator or the like and generates a first carrier wave.

An input terminal 11 inputs a signal wave for AC modulation having a relatively low frequency to the variable frequency oscillator 4. A capacitor C1 is provided between the input terminal 11 and the variable frequency oscillator 4.

The first frequency divider 3 divides the output of the first variable frequency oscillator 4, that is, the first modulated output. Reference numeral 1 in the figure is a reference oscillator, and the first phase comparator 2 compares the output from the reference oscillator 1 and the output from the first frequency divider 3 in phase and outputs the result.

The first low pass filter 9 is disposed between the first phase comparator 2 and the first frequency variable oscillator 4 and has an input terminal.
It is for removing the frequency related to the signal wave input from 11. In other words, lowpass filter 9
Is for synchronizing the first frequency variable oscillator 4 with the reference oscillator 1 so as not to follow the signal wave of the AC signal applied from the input terminal 11.

The second frequency divider 5 outputs the output of the first frequency variable oscillator 4,
That is, the first modulated output is divided.

The second frequency variable oscillator 8 is composed of a voltage controlled oscillator or the like and generates a second carrier wave. An output terminal 12 sends the output of the second variable frequency oscillator 8, that is, the second modulated output to the outside. Although not shown,
The second frequency variable oscillator 8 has an input terminal and inputs a signal wave for modulation having a relatively high frequency.

The variable frequency divider 7 divides the output of the second frequency oscillator 8 into a constant frequency.

The second comparator 6 compares the output from the variable frequency divider 7 and the output from the second frequency divider 5 in phase, and outputs the result. In other words, the second comparator 6 outputs a signal corresponding to the signal wave input from the input terminal 11.

The second low-pass filter 10 is arranged between the second phase comparator 6 and the second frequency variable oscillator 8 and has an input terminal.
It is for passing the frequency related to the signal wave input from 11.

In other words, the low-pass filter 10 follows the signal wave for AC modulation applied from the input terminal 11 so that the second variable frequency oscillator 8 is modulated.

In this embodiment as described above, the output of the reference oscillator 1 and the first
The output of the frequency variable oscillator 4 via the frequency divider 3 is input to the phase comparator 2 so that the output of the phase comparator 2 does not follow the AC modulation signal applied to the first frequency variable oscillator 4. It is input to the variable frequency oscillator 4 through the low-pass filter 9. That is, it is synchronized with the reference oscillator 1.

The output of the second variable frequency oscillator 8 is input to the phase comparator 6 after being made a constant frequency by the variable frequency divider 7. The output of the first variable frequency oscillator 4 is also input to the phase comparator 6 through the frequency divider 5. Therefore, the output of the phase comparator 6 outputs a signal corresponding to the AC modulation signal, and the second low-pass filter 10 is configured to pass a frequency higher than the modulation frequency. 8 is modulated.

The first variable frequency oscillator 4, the first frequency divider 3, the first phase comparator 2, and the first low pass filter 9 are provided.
Has a first frequency variable oscillator for inputting a signal wave for modulation, constitutes first phase synchronizing means for phase-locking with the output of the reference oscillator without following the signal wave, and
The frequency divider 5, the second variable frequency oscillator 8, the variable frequency divider 7, the second phase comparator 10, and the second low pass filter 10 have a second frequency variable oscillator for the carrier wave. , A second phase synchronization means for performing phase synchronization by following the output modulated by the signal wave from the first frequency variable oscillator.

〔The invention's effect〕

As described above, the present invention is economical because the reference oscillator is not directly modulated and one reference oscillator can be used for the reference oscillator. In addition, the frequency of the carrier is Since the frequency band of the loop for phase synchronization between the frequency variable oscillator No. 2 and the first frequency variable oscillator having the modulation terminal can be raised to the modulation frequency, there is an effect that it can be changed quickly.

In other words, since the present invention has two phase locked loops, the stability of the carrier wave is determined by the stability of the reference oscillator, so that it can be improved by using a reference oscillator with good stability. Also, even if the modulation frequency is extended to the reduction, it is not necessary to go down the cutoff frequency of the second low-pass filter in the PLL loop of the carrier wave.
It takes only a short time to switch the carrier frequency.

Further, since the carrier liquid is output by the single second frequency variable oscillator, there is an effect that spurious is not generated unlike the mixing method.

[Brief description of drawings]

 FIG. 1 is a block diagram of an embodiment according to the present invention. 1: Reference oscillator, 2, 6: Phase comparator 3, 5: Frequency divider, 4, 8: Variable frequency oscillator 7: Variable frequency divider, 9, 10: Low pass filter.

Claims (1)

[Claims] 1. A reference oscillator, a reference oscillator that generates a constant clock pulse, a first phase comparator that inputs the clock pulse and a first frequency-divided signal, and outputs a first phase difference signal, A first low-pass filter that inputs the first phase difference signal, cuts off the frequency of the input wave signal included in the phase difference signal, and generates a clock pulse tracking signal; and the clock pulse tracking with the input wave signal. A first frequency variable oscillator that modulates a signal to generate a modulated wave, and a first frequency divider that divides the modulated wave with a first constant frequency division ratio and outputs the first frequency-divided signal. A second phase divider that divides the modulated wave by a second constant division ratio and outputs a second divided signal; Input the signal and the frequency switching signal,
A second phase comparator for outputting a second phase difference signal; and the first low-pass filter for inputting the second phase difference signal and passing the modulated wave included in the second phase difference signal. A second low-pass filter set to a cut-off frequency higher than the cut-off frequency of the filter, and a second frequency variable that inputs the output of the second low-pass filter and generates a modulator output signal synchronized with the clock pulse. Second phase synchronization means having an oscillator and a variable frequency divider for inputting the modulator output signal and changing a frequency division ratio based on the frequency of a carrier wave to generate the frequency switching signal. Modulator.