JPH01129514A - Fsk modulator - Google Patents

Abstract

PURPOSE:To suppress spurious generation, and also, to respond to a quick modulating signal by supplying the output of a phase comparator to a loop filter through an analog switch, and executing the conduction control of the analog switch and the oscillation control of a voltage control oscillator by a modulating signal. CONSTITUTION:A reference oscillator 21 by a crystal resonator oscillates by a reference frequency. An analog switch 7 transfers the output signal of a phase comparator 3 to a loop filter 4 at the time of conducting. Also, to a conduction control terminal of this analog switch 7, a modulating signal input terminal 11 is connected, and the analog switch 7 is controlled so as to go to a conducting state and a non-conducting state, when a modulating signal is '0', and when the modulating signal is '1', respectively. A voltage control oscillator 2 has two pieces of control input terminals, and to a first control input terminal, the output terminal of the loop filter 4 is connected, and to a second control input terminal, the modulating signal input terminal 11 is connected. An output signal of the voltage control oscillator 25 is outputted to a modulated signal output terminal 12, and also, inputted to a second frequency divider 6.

Description

[Detailed Description of the Invention] "Field of Industrial Application" This invention is directed to
The present invention relates to an SK (frequency shift keying) modulator.

“Conventional technology” Conventionally, FSK modulators have a pr
, r, (phase-locked loop) configuration is used.

FIG. 2 is a block diagram showing the configuration of a conventional FSX modulator. 1 is a voltage controlled crystal oscillator, the oscillation frequency of which is controlled by the voltage applied to the modulation signal input terminal I+. 2 is a first frequency divider, which divides the output signal of the voltage controlled crystal oscillator 1 into M frequencies. The output signal of the first frequency divider and the output signal of the second frequency divider (described later) are input to the phase comparator 3, and a signal corresponding to the phase difference between the two signals is output. The loop filter 4 receives the output signal of the phase comparator 3,
The integrated waveform is output. The voltage controlled oscillator 5 receives the output signal of the loop filter 4 and oscillates at a frequency corresponding to the voltage value of the output horn signal. The output signal of the voltage controlled oscillator 5 is outputted to the modulated signal output terminal 12 and also inputted to the second frequency divider 6 . The second frequency divider 6 receives the output signal of the voltage controlled oscillator 5, divides it by N, and outputs it.

Then, the output signal of this second frequency divider is fed back into the phase comparator 3 mentioned above. A- That is, the phase comparator 3, the loop filter 4, the voltage controlled oscillator 5, and the second frequency divider 6 constitute P L, L.

The operation of this FSX modulator will be explained below. During non-modulation, the voltage controlled crystal oscillator 1 is supplied with a predetermined voltage from the modulation signal input terminal 11 and oscillates at the reference frequency fvcxo. Then, this frequency is divided by M by the first frequency divider 2, and a signal having a frequency of frel'-rvcxo/M is given to the phase comparator 3. As a result, when the oscillation frequency of the voltage controlled oscillator 5 becomes fout-N
ref, the phases of both forces of the phase comparator 3 match, and PLL is in a locked state. Then, a modulated signal with a frequency of foul is output from the modulated signal output terminal 12. For example, the frequency division ratio N is 72000, the frequency division ratio M
1024, reference frequency fvcx.

is 12.8MHz, fref12.5kl(z
Therefore, the modulated signal frequency is fout = 900.0
00MHz.

When performing FSK modulation, modulation signal input terminal 1
By changing the voltage value of 1 by a certain amount in response to the modulation signal binary data ``0'' and ``1'',
The oscillation frequency fvcxo of the voltage controlled oscillator 5 is changed by △fvcxo (J. As a result, the frequency fref of the signal given to the phase comparator 3 changes, and the oscillation frequency ro of the voltage controlled oscillator 5 changes.
With ut shifted by △rout, p r,, r
, is locked. Then, a modulated signal whose frequency is shifted by Δrout is obtained from the modulated signal output terminal 12. For example, under the above conditions, the variation ΔfvCxo in the oscillation frequency fvcxo of the voltage controlled crystal oscillator 1 is ±351−
1 z, △rout=D−X△fvcxo−±2461Hz
--(1) frequency shift occurs in the modulated signal, FSK
Modulation is performed.

[Problems to be Solved by the Invention] By the way, in the conventional FSX modulator, unless the response speed of the PLL is sufficiently fast relative to the speed of the modulation signal, the PLL and L cannot follow changes in the modulation signal. No FSK modulation was performed. Therefore, it was necessary to set the time constant of the loop filter small to increase the response speed of PLT. However, if the time constant of the loop filter is made small, the output signal of the phase comparator will not be integrated sufficiently.
Since it is given to the voltage controlled oscillator in a state including the frequency component component rer, I'out+ of the frequency component of the modulated signal
There was a problem in that spurious signals were generated at the fref position.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an FSK modulator that can suppress the generation of spurious signals and can respond to fast modulation signals.

"Means for Solving the Problems" The present invention has a phase-locked loop including a phase comparator, a loop filter, and a voltage-controlled oscillator, and the oscillation frequency of the voltage-controlled oscillator is equal to 2 of the input modulation signal. In an F S In preparation for this, the voltage controlled oscillator has a first control input terminal to which the output of the loop filter is inputted as a first control voltage, and a second control input terminal to which the binary data is inputted as a second control voltage. The oscillation frequency is controlled by cooperation of the first and second control voltages.

"Operation" According to this configuration, when the switch means is closed due to binary data switching of the modulation signal, the first control voltage applied to the voltage controlled oscillator is the voltage controlled by PLL. , and when the switch means is opened, the voltage controlled by the previous P L L is the voltage held by the loop filter. The oscillation frequency of the voltage controlled oscillator is controlled by the cooperation of this first control voltage and the voltage of the binary data of the input modulation signal. becomes the frequency.

[Embodiment 1] An embodiment of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an FSK modulator according to an embodiment of the present invention. In this figure, parts corresponding to those in FIG. 2 described above are designated by the same symbols. f and omit its explanation.

21 is a reference oscillator using a crystal oscillator, which oscillates at a reference frequency rx. The analog switch 7 transfers the output signal of the phase comparator 3 to the loop filter 4 when it is conductive. A modulation signal input terminal 11 is connected to the conduction control terminal of this analog switch 7, so that when the modulation signal is 10'', it is in a conductive state, and when the modulation signal is rlJ, it is in a non-conductive state. The analog switch 7 is controlled.The voltage controlled oscillator 25 has two control input terminals, the first
The second control input terminal is connected to the output terminal of the loop filter 4, and the modulation signal input terminal 11 is connected to the second control input terminal. The first control input terminal is provided with a first variable capacitance diode (not shown) whose capacitance value is controlled by the output voltage of the loop filter 4, and the second control input terminal is provided with a modulation capacitance diode (not shown). A second variable capacitance diode (not shown) whose capacitance value is controlled by the voltage of the signal is provided. These 11th and 2nd
The variable capacitance diodes are connected in parallel to form a resonant circuit for determining the oscillation frequency of the voltage controlled oscillator 25.

Therefore, the oscillation frequency of the voltage controlled oscillator 25 is controlled by the output voltage of the loop filter 4 and the voltage of the modulation signal. The output signal of the voltage controlled oscillator 25 is output to the modulated signal output terminal 12 and is also input to the second frequency divider 6.

The operation of this FSX modulator will be explained below. First, when the modulation signal is "0", the analog switch 7 is conductive, and the phase comparator 3, loop filter 4, and voltage controlled oscillator 2
5. The second frequency divider 6 constitutes PLL. At this time, the modulated signal frequency fout is as follows: 18=fout=NXrrer-groupXfx (2), and PLT is in a locked state.

Further, in this locked state, the output voltage of the loop filter 4 is held at a constant value VL.

Now, when the modulation signal changes from "0" to "1" from this state, the analog switch 7 becomes non-conductive.

As a result, the connection between the phase comparator 3 and the loop filter 4 is cut off, and the loop of PLL becomes open. Then, the loop filter 4 continues to hold the voltage VL. Further, by changing the modulation signal from "10" to "1", the modulated signal frequency becomes rout+Δrout and is output to the modulated signal output terminal I2.

Next, when the modulation signal returns from "1" to "0" again, the analog switch 7 becomes conductive and the PLL loop closes again, and at the same time, the modulated signal output terminal 12 receives the frequency ro.
The modulated signal of ut is output. Further, this modulated signal is fed to the phase comparator 3 via the second frequency divider 6, and pr, r return to the original locked state very quickly.

As described above, this FSK modulator outputs a modulated signal in response to a modulation signal.

In the embodiment described below, the voltage controlled oscillator 25 has two control input terminals, and the output voltage of the loop filter 4 and the modulation signal are applied to different variable capacitance diodes. Alternatively, the voltage controlled oscillator 25 may have one control input terminal, and the output voltage of the loop filter 4 and the modulation signal may be superimposed thereon and applied to one variable capacitance diode.

"Effects of the Invention" As explained above, according to the present invention, in the PLL section of the FSK modulator, the output of the phase comparator is supplied to the loop filter via the analog switch, and the modulation signal is used to control the analog switch. Since conduction control and oscillation control of the voltage controlled oscillator are performed, the modulation speed is PLL
A modulated wave that is frequency shift modulated at a stable frequency can be obtained without being constrained by the response speed. Furthermore, since the time constant of the loop filter can be set large, spurious generation can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an FSX modulator according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a conventional FSK modulator. 3...Phase comparator, 7...Analog switch, 4...Loop filter, 25...Voltage controlled oscillator Applicant Alps Electric Co., Ltd. Representative Katsuta Katakabe Figure 1 Figure 2

Claims (1)

[Claims] An FSK modulator that has a phase-locked loop that includes a phase comparator, a loop filter, and a voltage-controlled oscillator, and the oscillation frequency of the voltage-controlled oscillator is frequency shift modulated according to binary data of an input modulation signal. A switch means that is opened by one value of the binary data and closed by the other value is provided between the phase comparator and the loop filter, and the voltage controlled oscillator is configured such that the output of the loop filter is a first control input terminal to which one control voltage is input; and a second control input terminal to which the binary data is input as a second control voltage; An FSK modulator characterized in that the oscillation frequency is controlled by the action of the FSK modulator.