JPS63198406A - Broad band fm modulator - Google Patents

Abstract

PURPOSE:To improve the frequency stability over a broad band by controlling a frequency division ratio of each variable frequency divider for a frequency shift keying (FSK) signal generating circuit and a PLL loop depending on the setting. CONSTITUTION:A reference signal from a reference oscillator 12 is processed by fixed frequency dividers 13, 14, 5, a variable frequency divider 6 and an LPF 7 to form a frequency shift signal, which is synthesized with a reference signal through the fixed frequency divider 10 and an LPF 11 by a frequency synthesizer 8, becomes an FSK signal subject to frequency modulation via a BPF 9 and fed to a phase comparator 19 of a PLL provided with the variable frequency divider 17 in the feedback loop. The frequency division ratio of the frequency divider 17 and the frequency divider 6 is controlled via an arithmetic unit 21 depending on the setting from a frequency setting input terminal 20 and the frequency shift of the frequency modulation wave is subject to automatic control corresponding to the output frequency. As a result, the frequency stability over the broad band is improve and the modulation characteristic is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a frequency modulator (FM) device, and in particular, wideband frequency modulation using a PLL method suitable for expanding the frequency range, frequency stability, and modulation characteristics. Concerning vessels.

[Prior Art] Conventionally, this type of modulator is disclosed in Japanese Patent Application Laid-Open No. 61-71706.
a second frequency divider that divides the output of the variable phase shifter connected to the output of the first frequency divider that divides the oscillation output of the reference oscillator as described in the i! Compare the phase of the output of the second frequency divider with the output of a third frequency divider that divides the output of the voltage controlled oscillator, remove unnecessary waves of the phase shifter, and connect to the control input of the voltage controlled oscillator. Modulators using a PLL system using a low-pass filter employ configurations such as (1) applying direct modulation to a voltage controlled oscillator, and (2) applying direct modulation to a reference oscillator. However, in the above configuration, no consideration was given to changes in the amount of frequency shift when operating in a wide band.

[Problems to be Solved by the Invention] The above-mentioned prior art does not take into account the frequency shift, and there is a problem in that the frequency shift changes for each set frequency.

An object of the present invention is to provide a frequency modulation device in which the amount of frequency deviation is constant regardless of the set frequency and has high frequency stability.

[Means for solving the problem] The above object is to remove unnecessary waves from the output of a reference frequency oscillator, a first frequency divider that divides the output of the reference frequency oscillator, and the first frequency divider. a first filter, the reference signal oscillator, a frequency synthesizer that combines the output of the first filter, and the output of the reference signal oscillator; and a sum or difference of the outputs of the frequency synthesizer. a second filter for selecting signal components; and l! a voltage controlled oscillator; a second frequency divider that frequency divides the output of the voltage controlled oscillator; a phase detector that compares the phase of the output of the second frequency divider; and a phase detector that removes unnecessary waves from the output of the phase detector. a filter connecting the reference input signal to the control input of the voltage controlled oscillator; FM modulating the reference input signal connected to the phase comparator by simultaneously changing the first and second frequency division ratios; This is achieved by changing the amount of frequency deviation for FM modulation according to the frequency division ratio set in the loop.

[Function] The FM modulator of the present invention adjusts the amount of deviation of the reference FM modulation by dividing the stable FM modulation output by a value equal to the frequency division ratio of the feedback loop. The signal output from the voltage controlled oscillator by combining the FM modulation output with the reference signal and selecting the sum or difference signal between the frequency-divided FM modulation output and the reference signal is the same as the reference signal. It is obtained by adding or subtracting the above-mentioned highly stable FM modulation output to the frequency division ratio times, and an FM modulation output having a frequency proportional to the frequency division ratio is obtained, and the frequency deviation of the FM modulation output is It remains constant without being influenced by.

[Example] An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram showing an embodiment of a modulator for FS according to the present invention. In FIG. 1, 1 is a modulation input terminal, 2 is a D flip-flop, 3 and 4 are Nant gates, 5 is a fixed frequency divider, is a variable frequency divider (first frequency divider) 7 is a low-pass filter, 8 is a frequency synthesizer, 9 is a band-pass filter, 1
0 is a fixed frequency divider, 11 is a low-pass filter, 12 is a reference oscillator, 13 and 14 are fixed frequency dividers, 15 is a low-pass filter, 16 is a voltage controlled oscillator, 17 is a variable frequency divider, 18 is an output terminal, and 19 is a A phase comparator, 20 a frequency setting input terminal, and 21 a fixed subtractor, respectively.

The oscillation frequency fB of the reference frequency oscillator 12 is divided into frequencies of 1/A and 1/B by fixed frequency dividers 13 and 14, respectively, and input to one input terminal of the Nant gates 3 and 4, respectively. On the other hand, the digital modulation signal applied to the input terminal 1 is input to the D terminal of the D flip-flop 2, and a signal synchronized with the output frequency of the reference frequency oscillator 12 is sent from the Q terminal to the other input of the Nantes gate 3. A signal which is synchronized with the output of the reference frequency oscillator 12 and whose phase is 180' different from the modulation signal is output from the Q terminal to the other input terminal of the Nant gate 4.

The Nant gates 3 and 4 receive the fA/A signal formed by the fixed frequency divider 13 and 14 by modulation signals having a different phase of 180" synchronized with the reference signal of the D flip-flop 2.
, f^/B signals are switched and FSX modulated and output to the fixed frequency divider 5. (At this time, if the difference between A and B is a multiple of 3, the continuity of the phase is maintained.) The fixed frequency divider 5 divides the FSX modulation signal input from the AND gates 3 and 4 into a phase Continuous center frequency fs = (A + B)
The frequency is divided into an FSK modulated signal of fs/2A B and output to the variable frequency divider 6. The FSX modulated signal is frequency-divided by a variable frequency divider 6 at a frequency division ratio N to be described later, and then unnecessary waves are removed by a low-pass filter and input to a one-frequency synthesizer 8.

The other input signal of the frequency synthesizer 8 is a step frequency fc= which is obtained by dividing the output of the reference frequency oscillator 12 to 1/D by a fixed frequency divider 10 and removing unnecessary waves by a low-pass filter 11. fA/D is input. This step frequency fC is frequency-synthesized with the output signal of the low-pass filter 8 by a frequency synthesizer 8, and a band-pass filter 9 extracts only the sum component (or difference component) of the frequencies. =fc+fB is an FSK modulated signal, which is input to one terminal of the phase comparator 19.The phase comparator 19 is a low-pass filter 15. A PLL loop is formed together with the voltage controlled oscillator 16 and the variable frequency divider 17, and the oscillation frequency f0 of the voltage controlled oscillator 16 is divided by N and a frequency of -f,/N is applied to the other input terminal. The output of the generator 19 becomes a voltage according to the frequency and phase difference between the FSK modulation signal fD and f11/N, and is fed back to the voltage controlled oscillator. Therefore, the signal applied to the output terminal 18 becomes an FSK modulated wave, and its frequency f6 is calculated as f0=((A+B)fA12AB)+fcN...old...(1).

On the other hand, when a numerical value M is input to the frequency setting input terminal 20, the frequency division ratio N of the variable frequency dividers 6 and 17 is subtracted by the fixed subtracter 21, and N=M-(A+B)D/2AB・・・・・・・・・・
Old... (2) becomes, and when this is substituted into equation (1), f
,=fc−Mten(f^−Dfc)(A+B)/2AB”
=(3) Again.

Since D=fA/fc, f,=f(HM-M ・・・・・・・・・・・・・・・
(4) The center frequency f0 of the signal applied to the output terminal 18 is
The frequency is fc times the numerical value M input to the frequency setting input terminal 20. Further, if the shift frequency of the signal applied to the phase comparator 19 is fiz, fs, = (f^/A-fA/B)/CN- = (5), and this signal is applied to the PLL loop. Therefore, the shift frequency f811 of the output signal appearing at the output terminal 18 is multiplied by 8 by the voltage controlled oscillator, so that fiz == f s
-X N = (B-A) f A / A B C...
...'' (6), and a constant shift frequency is always output regardless of the setting input of the frequency setting input terminal 20.

According to this embodiment, one reference oscillator provides a reference FS.
Since the X signal is formed or the FSX modulated wave is frequency-divided, it is possible to obtain a highly stable FSK signal with continuous phase, and
Even if the output frequency is varied over a wide range, the shift frequency does not change, so a highly stable FSX modulation signal can be obtained.

[Effects of the Invention] According to the present invention, frequency modulation is applied to the reference input of the PLL loop, and the frequency deviation of this frequency modulated wave is automatically controlled in accordance with the output frequency, so that frequency stability is maintained over a wide frequency range. It is possible to obtain a frequency modulated wave with a high frequency, good modulation characteristics, and few spurious components.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an FSX modulator showing one embodiment of the present invention. 5, 10.13.14...Fixed frequency divider, 6,17.
...Variable frequency divider, 12...Reference oscillator, 19...
Phase comparator, 16...voltage controlled oscillator, 21... fixed subtractor. Patent Applicant Hitachi Shonan Electronics Co., Ltd. Representative Patent Attorney Tadashi Akimoto 1 other person

Claims (1)

[Claims] 1. a reference frequency oscillator, a first frequency divider that divides the output of the reference frequency oscillator, a first filter that removes unnecessary waves from the output of the first frequency divider, the reference signal oscillator, and the a frequency synthesizer that combines the output of the first filter and the output of the reference signal oscillator; and a second filter that selects either the sum or difference signal component from the output of the frequency synthesizer; a voltage controlled oscillator; a second frequency divider that divides the output of the voltage controlled oscillator; a phase detector that compares the phases of the outputs of the second filter and the second frequency divider; a filter that removes unnecessary waves from the output and connects it to a control input of the voltage controlled oscillator, and modulates the voltage controlled oscillator by simultaneously changing the first and second frequency division ratios. A wideband FM modulator characterized by: