JP2002290155A - Fm modulation device and frequency control method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the lock up time of a phase-locked loop at change of frequency, without having to switch loop constitution. SOLUTION: An FM modulation device is provided with an FM modulation circuit, which FM-modulates an input signal and the phase-locked loop for converting the frequency of an output signal from the FM modulation circuit; and when the output frequency of the phase-locked loop is changed, a non- modulation signal is outputted from the FM modulation circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM modulator and a frequency control method for the FM modulator, and more particularly to an FM modulator capable of changing a frequency used in a transmitter for terrestrial microwave communication and satellite communication. The present invention relates to a modulation device.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a configuration of a conventional FM modulator, which is disclosed in Japanese Patent Application Laid-Open No. 56-116307. In the figure, 51 is a subsynthesizer, 52 is a mixer, 53 is a main oscillator, 54 is an output terminal, 55 is a DC amplifier, 56 and 57 are low-pass filters, 58 is a phase detector, 59 is an FM modulation oscillator, 6
0 and 61 are frequency dividers, 62 is a frequency change confirmation circuit, 63 is a switch switching circuit, and SW1 to SW7 are changeover switches.

The signal generated in the main oscillator 53 is divided into two parts, one of which is output as an output signal to an output terminal 54 and the other is input to a mixer 52. In the mixer 52, the frequency signal from the sub-synthesizer 51 and the output signal of the main oscillator are mixed, and a signal having a difference frequency between the two signals is generated. Unnecessary signals are removed from this signal by the low-pass filter 57, and the signal is sent to the phase detector 58.

A phase detector 58 is provided with an oscillator 59 for FM modulation.
Is compared with the output signal of the low-pass filter 57, and the phase error signal is converted to the low-pass filter 56,
The signal is fed back to the main oscillator 53 via the DC amplifier 55.

When the switches SW1 to SW7 are turned to the side a, the cutoff frequency of the closed loop transfer characteristic becomes F
The characteristics of the low-pass filter 56 and the amplification of the DC amplifier 55 are determined so that the maximum frequency of the M-modulated signal is sufficiently passed and becomes sufficiently lower than the minimum frequency when the signal is tilted to the b side.

When the switches SW1 to SW7 are turned to the b side, the FM modulation distortion characteristic and the FM isolation characteristic are good, but the response of the PLL is very slow. For this reason, the changeover switches SW1 to SW7 are turned to the a side only for a certain period of time when the frequency is changed, and are returned to the b side after the frequency is stabilized.

[0007]

Since the conventional FM modulator is constructed as described above, it is composed of two types of phase-locked loops. When changing the frequency, the changeover switches SW1 to SW7 are controlled. Therefore, it was necessary to switch the loop configuration, and it was necessary to control many changeover switches.

Further, since the phase locked loop is switched by switching the changeover switches SW1 to SW7, there is a problem that when changing the frequency, the phase of the phase locked loop is disturbed and does not become continuous. For example, a problem arises when an image signal including a synchronization signal is FM-modulated and transmitted.

Furthermore, since the frequency converter is used in the phase locked loop, there is a problem that if the main oscillator 53 can oscillate at the frequency of the FM modulation signal, a pseudo lock occurs in the phase locked loop. Was.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an FM modulation apparatus in which the lockup time of a phase locked loop at the time of frequency change is reduced without switching the loop configuration. . Also,
An object of the present invention is to provide an FM modulator in which a pseudo lock of a phase locked loop at the time of frequency change is suppressed, and a lockup time of the phase locked loop is reduced.

[0011]

According to a first aspect of the present invention, there is provided an FM modulation apparatus comprising: an FM modulation circuit for FM-modulating an input signal; and a phase-locked loop for performing frequency conversion on an output signal of the FM modulation circuit. And when the output frequency of the phase locked loop is changed, a non-modulated signal is output from the FM modulation circuit.

With such a configuration, normally, the FM modulation circuit performs FM modulation of the input signal, and the phase locked loop performs frequency conversion on the modulation signal, thereby obtaining an FM modulation signal of a desired frequency. On the other hand, when changing the output frequency of the phase locked loop, an unmodulated signal is input from the FM modulation circuit to the phase locked loop. By inputting an unmodulated signal without frequency shift to the phase locked loop at the time of frequency change, the lockup time of the phase locked loop at the time of frequency change can be reduced. This unmodulated signal may be input to the phase locked loop for a predetermined time after the frequency change, for example.

According to a second aspect of the present invention, in the FM modulator, the phase locked loop includes a loop filter for feeding back a phase error signal corresponding to an output signal of the FM modulation circuit to the voltage controlled oscillator, and the output frequency of the phase locked loop is controlled. Is changed to reduce the time constant of the loop filter.

With such a configuration, the time constant is shortened to lock-up time until the phase locked loop is locked after the frequency is changed, while the time constant is lengthened after the lock to increase the phase locked loop. , And the loop band is narrowed to suppress out-of-band spurious. The time constant of the loop filter is, for example,
What is necessary is just to reduce by a predetermined time after a frequency change.

According to a third aspect of the present invention, there is provided an FM modulator for FM-modulating an input signal, a synthesizer for generating a predetermined frequency signal, and an output of the FM modulator using an output signal of the synthesizer. A phase locked loop that performs frequency conversion on the signal, and the synthesizer
A frequency signal is generated based on the frequency control signal, and the FM modulation circuit is configured to output an unmodulated signal when the output frequency of the phase locked loop is changed based on the frequency control signal.

With such a configuration, the synthesizer supplies a frequency signal corresponding to the output frequency of the phase locked loop to the phase locked loop based on the frequency control signal, and the phase locked loop generates the frequency signal based on the frequency signal from the synthesizer. F
Frequency conversion is performed on the output signal of the M modulation circuit. That is, the output frequency of the phase locked loop is determined based on the frequency control signal. Therefore, the FM modulation circuit outputs an unmodulated signal based on the frequency control signal,
When the output frequency of the phase locked loop is changed, an unmodulated signal can be input to the phase locked loop. The unmodulated signal may be input to the phase locked loop for a predetermined time after the frequency change signal is instructed by the frequency control signal, for example.

According to a fourth aspect of the present invention, an FM modulator according to the present invention includes switching means for selectively outputting an input signal or a predetermined constant signal to an FM modulator based on a frequency control signal.

With such a configuration, the switching means normally inputs an input signal to the FM modulator based on the frequency control signal, and outputs a constant signal when the output frequency of the phase locked loop is changed. Input to FM modulator. Therefore, it is possible to output an unmodulated signal from the FM modulator to the phase locked loop when the output frequency is changed.

According to a fifth aspect of the present invention, there is provided an FM modulation apparatus, wherein a phase locked loop includes a loop filter, and the loop filter feeds back a phase error signal corresponding to an output signal of the FM modulation circuit to a voltage controlled oscillator. The time constant is reduced when the output frequency of the phase locked loop is changed based on the frequency control signal.

With such a configuration, the time constant of the loop filter can be reduced when changing the output frequency of the phase locked loop based on the frequency control signal. In other words, the lockup time is shortened by shortening the time constant until the phase locked loop locks after the frequency change, while the time constant is lengthened after the lock to stabilize the phase locked loop and Out of band spurious can be suppressed by narrowing the band. The time constant of the loop filter may be reduced, for example, by a predetermined time from the frequency change.

According to a sixth aspect of the present invention, an FM modulator includes an offset signal source for supplying an offset signal corresponding to an output frequency to a phase locked loop based on a frequency control signal. The adder is configured to add the output signal of the offset signal source to the phase error signal with respect to the output signal of the FM modulation circuit, and to feed back to the voltage controlled oscillator.

With such a configuration, the offset signal source supplies an offset signal corresponding to the output frequency to the phase locked loop, and the adder forming the phase locked loop has the FM
The offset signal is added to the phase error signal for the output signal of the modulation circuit, and the result is fed back to the voltage controlled oscillator. That is, since the offset signal is also changed in accordance with the change in the output frequency of the phase locked loop, it is possible to reduce the frequency fluctuation width of the phase locked loop when the output frequency is changed and to reduce the frequency of occurrence of the pseudo lock. it can. The offset signal is controlled to be, for example, a value corresponding to the output frequency of the phase locked loop or a value close to the value.

According to a seventh aspect of the present invention, an FM modulator includes an offset signal source for supplying an offset signal corresponding to an output frequency to a phase locked loop based on a frequency control signal. The adder is configured to add the output signal of the offset signal source to the output signal of the loop filter and feed it back to the voltage controlled oscillator.

According to the present invention, there is provided an FM modulator comprising: an adder for adding an output signal of an offset signal source to an output signal of a loop filter; detecting means for detecting an output signal of the loop filter; Offset signal according to output frequency based on control signal
And an offset signal source for supplying the phase-locked loop to the phase-locked loop. The offset signal source is configured to change the offset signal based on a detection result of the output signal of the loop filter when the output frequency of the phase-locked loop is changed. You.

With such a configuration, it is possible to correct a deviation of the offset signal due to aging, temperature change, power supply voltage change and the like. For this reason, the lockup time of the phase locked loop at the time of changing the frequency is reduced, and the stability at the time of locking is improved.

According to a ninth aspect of the present invention, there is provided an FM modulation apparatus including an offset signal source for supplying an offset signal corresponding to an output frequency to a phase locked loop based on a frequency control signal. It is provided with an adder that adds the output signal of the offset signal source to the phase error signal and outputs the result to the loop filter.

With such a configuration, the phase error signal with respect to the output signal of the FM modulation circuit is fed back to the voltage controlled oscillator via the loop filter after the offset signal is added by the adder. Therefore, out-of-band noise included in the offset signal can be reduced by the loop filter.

According to a tenth aspect of the present invention, an FM modulator includes an adder that adds an output signal of an offset signal source to a phase error signal corresponding to an output signal of an FM modulation circuit and outputs the result to a loop filter; Detecting means for detecting an output signal; and an offset signal source for supplying an offset signal corresponding to the output frequency to the phase locked loop based on the frequency control signal, wherein the offset signal source changes the output frequency of the phase locked loop. At this time, it is configured to change the offset signal based on the detection result of the detection means.

With such a configuration, it is possible to correct a shift of the offset signal due to aging, temperature change, power supply voltage change and the like. For this reason, the lockup time of the phase locked loop at the time of changing the frequency is reduced, and the stability at the time of locking is improved.

According to an eleventh aspect of the present invention, in the FM modulator, the phase locked loop includes a frequency converter that mixes the output signals of the voltage controlled oscillator and the synthesizer, and the phase locked loop is provided via a high-pass filter or a band-pass filter. A frequency signal corresponding to the sum of the frequencies of the voltage controlled oscillator and the synthesizer is extracted from the output signal of the frequency converter.

With such a configuration, the output signal of the voltage controlled oscillator and the output signal of the high-pass filter or the band-pass filter can be used, and a wide output frequency can be obtained.

According to a twelfth aspect of the present invention, in the frequency control method for an FM modulator according to the present invention, an input signal is FM-modulated and
A modulation step of generating a modulation signal, a frequency conversion step of inputting an FM modulation signal to a phase locked loop and performing frequency conversion, and changing an output frequency of the phase locked loop and an unmodulated signal when changing the output frequency Is input to the phase locked loop.

According to a thirteenth aspect of the present invention, in the frequency control method of the FM modulator according to the present invention, the frequency changing step reduces a time constant of a loop filter constituting the phase locked loop when changing the output frequency of the phase locked loop. It is configured to

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a block diagram showing a configuration example of the FM modulation device according to the first embodiment of the present invention. In the figure, 11 is an FM modulator, 12 is a phase detector, 13 is a loop filter, 14 is an adder, 15 is a voltage controlled oscillator, 16 is a frequency converter, 17 is a band pass filter, 18 is D / A (Digital). / Analog) converter, 1
9 is a frequency control circuit, 20 is a frequency synthesizer, 21
Is a low-pass filter. L1 is a phase locked loop, SWa and SWb are changeover switches, and T1 to T4 are input / output terminals. Note that the broken lines in the figure indicate control signals.

The phase locked loop L1 includes a phase detector 12,
Loop filter 13, adder 14, voltage controlled oscillator 1
5. It is composed of a frequency converter 16 and a low-pass filter 21. This phase locked loop L1 is connected to the FM modulator 1
The frequency conversion is performed on the FM modulation signal output from No. 1.

The terminal T1 is an input terminal for an information signal modulated by the FM modulator of FIG. 1, and the baseband signal input from the terminal T1 is output to the FM modulator 11. Terminals T3 and T4 are output terminals of an FM modulation signal obtained by FM-modulating the baseband signal, and FM modulation signals having different frequencies are output from each terminal. For example,
When an image signal including a synchronization signal is input to the terminal T1 as a baseband signal, an FM modulated signal of a predetermined frequency is output to the terminal T1.
3 and output from T4. Here, the frequency of the FM modulation signal means the frequency of the carrier.

The terminal T2 is an input terminal to which a frequency control signal is input. The frequency control signal input from the terminal T2 is input to the frequency control circuit 19. The frequency control signal is a signal for controlling the frequency of the FM modulation signal output from the terminals T3 and T4, and the frequency of the output signal is changed based on the frequency control signal.

The switching switches SWa and SWb are switching means for selectively outputting one of the input signals from the two terminals a and b based on the switching control signal from the frequency control circuit 19. As for the changeover switches SWa and SWb, the terminal a is normally selected, and when the frequency is changed, the terminal b is selected for a predetermined period.

The switch SWa has an output terminal FM.
The terminal a is connected to the input terminal T
1 and the terminal b is grounded. For this reason, the changeover switch SWa operates the normal F based on the changeover control signal.
At the time of M modulation, the input signal from the input terminal T1 is output to the FM modulator 11, while at the time of frequency change, a constant potential level is output to the FM modulator 11 to create a no-signal state.

The changeover switch SWb is connected to the loop filter 1
This is a means for setting a time constant of 3 and selects one of two predetermined time constants. When the terminal b is selected, the time constant is configured to be smaller than when the terminal a is selected, and the time constant of the loop filter 13 becomes smaller than the normal time when the frequency is changed. . Here, an example in which the changeover switch SWb is used for controlling the time constant of the loop filter 13 will be described.
Another configuration may be adopted as long as the time constant of the loop filter 13 can be switched based on the switching control signal from the frequency control circuit 19.

The FM modulator 11 is a modulating means for FM-modulating an input signal from the changeover switch SWa as a baseband signal, and outputs an FM-modulated signal having a frequency fmod to the phase locked loop L1. However, when changing the frequency,
Since a signal of a certain level is input from the changeover switch SWa, the FM modulator 11 outputs a non-modulated signal (that is, a carrier wave) having a frequency fmod.

The frequency control circuit 19 switches the switches SWa and SWb and the D / A converter 1 based on the frequency control signal.
8 and a synthesizer 20 to control the output frequency of the phase locked loop. That is,
The output frequency of the phase-locked loop is determined based on the frequency control signal, and the setting and the change of the output are controlled by the frequency control circuit 19.

The synthesizer 20 includes a frequency control circuit 19
Generates a frequency signal designated by
Output to 6. The output signal of the synthesizer 20 has a frequency corresponding to the frequency conversion width (up-conversion width) in the phase locked loop L1, and this frequency is fsyn.

The D / A converter 18 includes a frequency control circuit 19
An analog voltage signal is generated based on a digital signal indicating a voltage level input from the controller and output to the adder. This analog signal is controlled to a voltage level corresponding to or near the output frequency of the voltage controlled oscillator.

The changeover switches SWa and SWb are switched to the terminal b when changing the output frequency of the phase locked loop L1 based on the switching signal from the frequency control circuit 19, and to the terminal a in other cases. Is done.

The voltage controlled oscillator 15 is a VCO (Voltage Control) whose oscillation frequency is controlled based on the input voltage level.
lled Oscillator), and its output signal is output to the terminal T3. The frequency converter 16 includes a voltage controlled oscillator 15
And a mixer that mixes the output signal of the synthesizer 20 with the output signal of the synthesizer 20. The output of the frequency converter 16 is a mixed signal composed of a frequency component corresponding to the sum of the frequencies of both signals and a frequency component corresponding to the difference between the frequencies of the two signals. Is output.

The low-pass filter 21 is a filter for selectively outputting a signal component of a predetermined frequency or less, and extracts the latter frequency component (a component corresponding to a frequency difference) from the output signal of the frequency converter 16. And outputs it to the phase detector 12. The phase detector 12 compares the phase of the output signal of the FM modulator 11 with the phase of the output signal of the low-pass filter 21,
A phase error signal corresponding to both phase errors is output.

The loop filter 13 can be configured as an integrating circuit for integrating the phase error signal, and converts the phase error signal into an averaged voltage signal according to a predetermined time constant. The adder 14 adds the voltage level output from the loop filter 13 and the voltage level value output from the D / A converter 18, and the operation result is fed back to the voltage controlled oscillator 15. That is, the output signal of the D / A converter is the offset value of the input signal to the voltage controlled oscillator 15.

The band-pass filter 17 is a filter for selectively outputting a frequency component within a predetermined band, and extracts the former frequency component (a component corresponding to the sum of frequencies) from the output signal of the frequency converter 16. Then, the signal is output to the terminal T4. Although a bandpass filter is used here,
If a high-pass filter is used instead, a component corresponding to the sum of frequencies can be extracted.

Assuming that the output frequency of the VCO 15 is fvco and the output frequency of the synthesizer 20 is fsyn, the output signal of the frequency converter 16 is a mixed signal composed of a signal of the frequency fvco + fsyn and a signal of the frequency fvco-fsyn. The cut-off frequency of the low-pass filter 21 is determined so that the frequency fvco-fsyn is extracted from the mixed signal. The cut-off frequency of the band-pass filter 17 is calculated based on the frequency fvco + f
It is decided to take out syn.

When the phase error signal from the phase detector 12 is sufficiently small and the phase locked loop L1 is locked, fmod = fvco-fsyn is established (fmo).
d is the output frequency of the FM modulator 11). At this time, the frequency from the output terminal T3 is fvco = fsyn + fmod.
Is output from the output terminal T4, and the frequency is fsyn + fvco = 2fsyn + fmod.
A modulated signal is being output. That is, a broadband FM signal is obtained at the terminal T4.

FIG. 2 is a timing chart showing an example of the operation when changing the output frequency of the phase locked loop L1 of FIG. In the figure, (a) shows the frequency control signal input to the terminal T2, (b) shows the output frequency of the synthesizer 20, (c) shows the output voltage of the D / A converter 18, and (d).
Is a switching control signal of the changeover switches SWa and SWb,
(E) shows the output signal of the FM modulator 11, and (f) shows the time constant of the loop filter 13.

The frequency control signal input from the terminal T2 includes designation of a new output frequency of the phase locked loop L1. After outputting a switching control signal to the changeover switches SWa and SWb based on the frequency control signal, the frequency control circuit 19 instructs the synthesizer 20 of a new frequency, and also outputs a new frequency to the D / A converter 18. Indicate the offset value.

Switch SW for selecting terminal a side
a and SWb select the terminal b based on the switching control signal. Therefore, the FM that outputs the FM modulation signal
The modulator 11 outputs a non-modulated signal, and the time constant of the loop filter 13 decreases. After that, the frequency of the output signal of the synthesizer 20 changes, and the output level of the D / A converter 18 changes.

When the frequency of the synthesizer 20 changes, the phase locked loop L1 enters the unlocked state. At this time, a non-modulated signal is input to the phase detector 12 from the FM modulator 11, and no frequency shift due to the input signal from the terminal T1 occurs in the phase locked loop L1. Further, the time constant of the loop filter 13 is reduced. Therefore, the lockup time of the phase locked loop L1 is reduced.

Further, when the phase locked loop L1 enters the unlocked state, the D / A converter 18 outputs a new offset value. This offset value is set to the new oscillation frequency of the voltage controlled oscillator 15, that is, the center of the new frequency output from the terminal T3. As a result, the phase error signal of the phase detector 12 in the unlocked state can be reduced, and the apparent frequency difference can be reduced as compared with the actual frequency difference before and after the change. The time can be reduced, and the occurrence of a pseudo lock can be suppressed.

When a sufficient time elapses after the phase locked loop L1 enters the unlocked state and locks, the frequency control circuit 19 outputs a switching control signal to the changeover switches SWa and SWb. The changeover switches SWa and SWb that have selected the terminal b side select the terminal a side based on this switching control signal.

For this reason, the FM that outputs the unmodulated signal
The modulator 11 outputs an FM modulated signal,
The time constant of the loop filter 13 increases. That is, in the normal state in the locked state, the phase locked loop is stabilized and the loop band is narrowed, so that out-of-band spurious can be suppressed.

According to the present embodiment, the phase locked loop L
When changing the output frequency of No. 1, an unmodulated signal is input from the FM modulator 11 to the phase detector 12 of the phase locked loop L1. Therefore, there is no frequency shift in the phase locked loop in the unlocked state, and the lockup time of the phase locked loop L1 can be reduced.

When the output frequency of the phase locked loop L1 is changed, the time constant of the loop filter 13 for feeding back the phase error signal to the voltage controlled oscillator 15 is changed so that the time from the frequency change to the lock is shortened. The rest is longer. For this reason, the lock-up time can be shortened, stabilization at the time of locking can be achieved, and the loop band can be narrowed to suppress out-of-band spurious.

Further, since the offset value of the D / A converter 18 is added to the phase error signal and is fed back to the voltage controlled oscillator 15, when the output frequency of the phase locked loop L1 is changed, the D / A conversion is performed. The offset value supplied from the adder 18 to the adder 14 is set at the center of the new frequency.
For this reason, the apparent frequency difference at the time of frequency change can be reduced, the lock-up time can be shortened, and the occurrence of pseudo lock can be suppressed.

Further, in the present embodiment, unlike the conventional FM modulator, the loop switching is not performed when the output frequency of the phase locked loop is changed. For this reason, the phase is continuous, and the amount of phase change at the time of switching the time constant of the loop filter can be reduced.

In the present embodiment, various methods have been described for realizing a reduction in lock-up time without switching the loop when changing the output frequency. Although it is desirable to employ all of these methods, the present invention is not limited to such a case, and any one of the methods can be employed alone, or two or more can be employed in combination.

Embodiment 2 FIG. 3 is a block diagram showing one configuration example of the FM modulator according to the second embodiment of the present invention. In the figure, 11 is an FM modulator, 12 is a phase detector,
13 is a loop filter, 14 is an adder, 15 is a voltage controlled oscillator, 16 is a frequency converter, 17 is a band-pass filter, 18 is a D / A converter, 19 is a frequency control circuit, 20
Is a frequency synthesizer, and 21 is a low-pass filter. L2 is a phase locked loop, SWa and SWb are changeover switches, and T1 to T4 are input / output terminals. Comparing the phase locked loop L2 in the figure with the phase locked loop L1 in FIG. 1, the position of the adder 14 forming the loop is different.

In the phase locked loop L2, an adder 14 is inserted between the phase detector 12 and the loop filter 13, and the adder 14 adds a D / A signal to the phase error signal output from the phase detector 12. The offset signal output from the converter 18 is added and output to the loop filter 13. Therefore, of the noise contained in the offset signal,
The out-of-band noise is input to the voltage-controlled oscillator 15 after being reduced by the characteristics of the loop filter 13.

According to the present embodiment, the adder 14
The offset signal from the D / A converter 18 is added to the phase error signal with respect to the output signal of the modulator 11 and output to the loop filter. For this reason, it is possible to improve the phase noise characteristic and the noise resistance characteristic of the FM modulator.

Embodiment 3 FIG. 4 is a block diagram showing a configuration example of the FM modulation device according to the third embodiment of the present invention. In the figure, 11 is an FM modulator, 12 is a phase detector,
13 is a loop filter, 14 is an adder, 15 is a voltage controlled oscillator, 16 is a frequency converter, 17 is a band-pass filter, 18 is a D / A converter, 19 is a frequency control circuit, 20
Is a frequency synthesizer, 21 is a low-pass filter, 22
Is an A / D converter. L2 is a phase locked loop,
SWa and SWb are changeover switches, and T1 to T4 are input / output terminals. 1 is different from FIG. 1 in that an A / D converter 22 is provided.

The A / D converter 22 detects a phase error signal input to the adder 14. That is, the phase error signal as an analog signal output from the loop filter 13 is converted into a digital signal and output to the frequency control circuit 19. The frequency control circuit 19 includes an A / D converter 22
Phase-locked loop L1
The offset signal of the D / A converter 18 is controlled so as to minimize the phase error in the above.

In this embodiment, the A / D converter 22 detects the output signal of the loop filter 13 and the frequency control circuit 19 changes the offset signal based on the detection result. It is added to the output signal. For this reason, it is possible to correct a shift of the offset signal caused by an aging of each element, a change in temperature, a change in power supply voltage, and the like. Therefore, the lockup time of the phase locked loop at the time of changing the frequency can be shortened, and the stability of the phase locked loop that can be normally set can be improved.

Embodiment 4 FIG. 5 is a block diagram showing one configuration example of the FM modulator according to the fourth embodiment of the present invention. In the figure, 11 is an FM modulator, 12 is a phase detector,
13 is a loop filter, 14 is an adder, 15 is a voltage controlled oscillator, 16 is a frequency converter, 17 is a band-pass filter, 18 is a D / A converter, 19 is a frequency control circuit, 20
Is a frequency synthesizer, 21 is a low-pass filter, 22
Is an A / D converter. L2 is a phase locked loop,
SWa and SWb are changeover switches, and T1 to T4 are input / output terminals. 3 is different from FIG. 3 in that an A / D converter 22 is provided, and compared with FIG. 4, the position of the adder 14 forming the phase locked loop is different.

The A / D converter 22 is connected to the voltage controlled oscillator 15
Is detected. That is, the phase error signal as an analog signal output from the loop filter 13 is converted into a digital signal and output to the frequency control circuit 19. The frequency control circuit 19 controls the D / A converter 1 based on the detection signal input from the A / D converter 22 so that the phase error in the phase locked loop L1 is minimized.
8 is controlled.

In this embodiment, the A / D converter 22 detects the output signal of the loop filter 13, the frequency control circuit 19 changes the offset signal based on the detection result, and converts the offset signal into the phase detector 12 Is added to the output signal. Therefore, aging of each element,
It is possible to correct a deviation of the offset signal caused by a temperature change, a power supply voltage change, or the like. Therefore, the lock-up time of the phase locked loop at the time of frequency change can be shortened, and the stability of the phase locked loop that can be normally set can be improved.

[0073]

The FM modulator according to the present invention includes an FM modulation circuit for FM-modulating an input signal, and a phase locked loop for performing frequency conversion on an output signal of the FM modulation circuit. When changing, an unmodulated signal is output from the FM modulation circuit. For this reason, when changing the output frequency of the phase locked loop, by inputting an unmodulated signal without frequency shift to the phase locked loop, the lockup time of the phase locked loop at the time of changing the frequency can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of an FM modulation device according to a first embodiment of the present invention.

FIG. 2 is a timing chart showing an example of an operation when changing the output frequency of the phase locked loop L1 of FIG.

FIG. 3 is a block diagram illustrating a configuration example of an FM modulation device according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration example of an FM modulation device according to a third embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration example of an FM modulation device according to a fourth embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a conventional FM modulator, which is disclosed in Japanese Patent Application Laid-Open No. 56-116307.

[Explanation of symbols]

11 FM modulator, 12 phase detector, 13 loop filter, 14 adder, 15 voltage controlled oscillator, 16
Frequency converter, 17 band pass filter, 18 D / A
Converter, 19 frequency control circuit, 20 frequency synthesizer, 21 low-pass filter, 22 A / D converter L1 and L2 phase locked loop, SWa and SW2b
Selector switch, T1-T4 I / O terminal

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Akio Iida 2-3-2 Marunouchi, Chiyoda-ku, Tokyo F-term in Mitsubishi Electric Co., Ltd. (reference) 5J106 AA04 BB01 CC01 CC41 DD08 DD13 DD44 GG07 HH01 KK03

Claims (13)

[Claims] An FM modulation circuit for FM-modulating an input signal, and a phase-locked loop for performing frequency conversion on an output signal of the FM modulation circuit, wherein when the output frequency of the phase-locked loop is changed, An FM modulator, which outputs a non-modulated signal. 2. The phase-locked loop according to claim 1, further comprising a loop filter for feeding back a phase error signal corresponding to an output signal of the FM modulation circuit to a voltage-controlled oscillator, wherein the time constant of the loop filter is changed when changing the output frequency of the phase-locked loop. The FM modulator according to claim 1, wherein the frequency is reduced. 3. An FM modulation circuit for FM-modulating an input signal, a synthesizer for generating a predetermined frequency signal, and a phase locked loop for performing frequency conversion on an output signal of the FM modulation circuit using an output signal of the synthesizer. In the FM modulator provided, a synthesizer generates a frequency signal based on the frequency control signal, and the FM modulation circuit outputs an unmodulated signal when the output frequency of the phase locked loop is changed based on the frequency control signal. An FM modulator characterized by the above-mentioned. 4. The FM modulator according to claim 3, further comprising switching means for selectively outputting an input signal or a predetermined constant signal to an FM modulator based on the frequency control signal. 5. The phase locked loop feeds back a phase error signal corresponding to an output signal of an FM modulation circuit to a voltage controlled oscillator, and sets a time constant when changing an output frequency of the phase locked loop based on a frequency control signal. The FM modulator according to claim 3, further comprising a loop filter for reducing the frequency. 6. An offset signal source for supplying an offset signal corresponding to an output frequency to a phase locked loop based on the frequency control signal, wherein the phase locked loop includes an FM signal.
4. The FM according to claim 3, further comprising an adder for adding the output signal of the offset signal source to the phase error signal corresponding to the output signal of the modulation circuit and feeding back the output signal to the voltage controlled oscillator.
Modulation device. 7. The FM according to claim 6, wherein the adder adds the output signal of the offset signal source to the output signal of the loop filter and feeds back to the voltage controlled oscillator.
Modulation device. 8. The FM modulator according to claim 7, further comprising a detection unit for detecting an output signal of the loop filter, wherein the offset signal source changes the offset signal based on a detection result of the detection unit. . 9. The FM modulator according to claim 6, wherein the adder adds an output signal of an offset signal source to a phase error signal corresponding to an output signal of the FM modulation circuit and outputs the result to a loop filter. . 10. The FM modulator according to claim 9, further comprising a detection unit for detecting an output signal of the loop filter, wherein the offset signal source changes the offset signal based on a detection result of the detection unit. . 11. The phase locked loop comprises a frequency converter for mixing output signals of a voltage controlled oscillator and a synthesizer, and corresponds to a sum of frequencies of the voltage controlled oscillator and the synthesizer via a high-pass filter or a band-pass filter. 11. The FM modulator according to claim 3, wherein a frequency signal to be extracted is extracted from an output signal of the frequency converter. 12. A modulation step of FM-modulating an input signal to generate an FM-modulated signal, a frequency conversion step of inputting the FM-modulated signal to a phase-locked loop and performing frequency conversion, and changing an output frequency of the phase-locked loop. Along with
A frequency changing step of inputting a non-modulated signal to a phase locked loop when changing an output frequency. 13. The FM modulator according to claim 12, wherein the frequency changing step reduces the time constant of a loop filter forming the phase locked loop when changing the output frequency of the phase locked loop. Frequency control method.