JPS6238883B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a device for generating a frequency modulated signal having a relatively low center frequency and having a signal waveform of the center frequency as a sine wave, and further relates to Specifically, a self-oscillating frequency modulator whose center frequency is higher than the center frequency, a reference input signal having a frequency equal to the center frequency, and an oscillation frequency of the self-oscillating frequency modulator. The output signal of this oscillator and the output signal of the self-excited oscillation type frequency modulator are respectively input to a phase detector via a frequency divider, and from this phase detector The comparison output signal of is fed back to the self-excited oscillation type frequency modulator, and the output signal frequency of this self-excited oscillation type frequency modulator is controlled to be equal to the generated signal frequency from the oscillator. After frequency-mixing the signal and the input signal, this mixed signal is passed through a bandpass filter and further frequency-mixed with the output signal of the self-oscillation type frequency modulator, which is equal to the frequency of the reference input signal. Frequency modulation signal generation which generates a frequency modulation signal with the center frequency as the center frequency, has high stability at the center frequency, and makes the output signal waveform of the center frequency a sine wave. Related to equipment.

[Prior art and its problems] Examples of frequency modulated signals that have a relatively low center frequency and require high stability include frequency modulated signals of SCA subcarriers (center frequency 67 KHz) used in FM broadcasting.

Furthermore, when using the above frequency modulated signal not for broadcasting but for adjusting a device under test such as a receiver, the signal waveform of the center frequency itself must be a sine wave. There may be cases where

Referring to Japanese Patent Publication No. 49-35865, the configuration of a conventional frequency modulation signal generator is shown in FIG. 2. In the figure, this device includes a self-oscillation type frequency modulator 10 that modulates a frequency fM higher than a predetermined center frequency fo with an input modulation signal received at a terminal 9, an output signal of this modulator 10, and an oscillator 12. Oscillation frequency from
a frequency mixer 11 for frequency mixing the signal fM±fo, an output terminal 13, and a frequency divider 14 for dividing the frequency fM of the signal from the self-oscillation type frequency modulator into 1/m; A phase detector 15, a reference crystal oscillator 16 that generates a reference signal whose oscillation frequency is a predetermined center frequency fo, and a frequency mixer 17 that mixes this reference signal with the signal from the oscillator.
and the frequency of the signal from this frequency mixer 17
The frequency divider 18 divides fM into 1/m, and the center frequency of the self-oscillation type frequency modulator 10 is controlled by the output DC signal of the phase detector.

In this way, in the conventional type, the output signal of the self-oscillation type frequency modulator whose center frequency is higher than a predetermined center frequency and the output signal of the frequency mixing oscillator are guided to the frequency mixer, and this frequency mixing is performed. A frequency modulation signal having a predetermined center frequency is output from the oscillator, and on the other hand, a reference signal having a frequency equal to the predetermined center frequency and the output signal of the frequency mixing oscillator are separately frequency-mixed. The signal and the output signal separately output from the frequency modulator are respectively guided to a phase detector via a frequency divider, and the output signal of this phase detector is fed back to the frequency modulator to generate a signal. The center frequency of the frequency modulated signal is controlled to match the frequency of the reference signal.

The above conventional type is also guaranteed to be effective in terms of highly stabilizing the center frequency, but in addition to achieving high stability, in order to make the signal waveform of the center frequency itself a sine wave, the following steps must be taken. It is necessary to meet the following technical conditions. That is, the two inputs in the first frequency mixer 11 are f ₁ and f ₂
Then, the outputs are f ₁ , f ₂ , f ₁ ±f ₂ , 2f ₁ ±f ₂ ,
After using a frequency mixer where either m or n is only 1 in the general formula for the frequency mixer output (mf 1 ±nf _{2 )} such as 3f ₁ ±f ₂ , the frequency Of the two inputs of the mixer, the side corresponding to m and n, which are 1, must be a sine wave signal.

However, in general, the output of a frequency modulator is not necessarily a sine wave, and especially when limiters are connected in series to remove amplitude modulated waves remaining in the modulated signal, the output signal will not be a sine wave signal. On the other hand, as a frequency mixing oscillator, it is customary to use an easily applicable type of oscillator, such as an unadjusted oscillation circuit, so the output waveform cannot be called a sine wave, but rather a rectangular one. The signal waveform is close to that of a wave.

In this way, since both of the two input signals to the final stage frequency mixer are not sine waves, the above conventional type satisfies this requirement in that the output signal waveform of the center frequency is a sine wave. I couldn't do it. In addition, if a frequency mixer is connected with a bandpass filter in order to make the output signal waveform a sine wave, the signal passing through the filter is a frequency modulated wave, so the delay time characteristics and attenuation characteristics within the passband are extremely low. requires advanced technology. In particular, this may not be possible if there is no large difference between the center frequency and frequency deviation.

[Summary of the Invention] Here, the present invention provides that, of the two input lines to the frequency mixer disposed at the final stage, a second frequency The configuration is such that a bandpass filter with a relatively narrow bandwidth can be connected to the output side of the mixer, thereby converting the signal waveform at the center frequency of the generated frequency modulated signal into a sine wave without increasing the number of circuit elements. The present invention attempts to provide a frequency modulation signal generation device that can generate waves.

[Example] The present invention will be specifically described below with reference to an example shown in FIG. In the figure, the symbol IN is an input terminal for a modulation signal wave, and this input terminal IN is connected to a self-excited oscillation type frequency modulator FM. This self-oscillating frequency modulator FM has a center frequency fm (fm≫fo) higher than a predetermined center frequency fo (described later), and has an output terminal connected to the first frequency mixer MIX ₁ . .

On the other hand, an oscillator OSC ₁ that generates a reference signal with a frequency equal to the predetermined center frequency fo and an oscillator OSC ₂ that generates a signal with a frequency equal to the center frequency fm of the self-oscillating frequency modulator FM are separately operated. 2
In addition to connecting to frequency mixer MIX ₂ , this second
The output terminal of the frequency mixer MIX ₂ has a center frequency set to the sum frequency fm+fo or the difference frequency fm−fo among the output signal frequencies fm±fo of the second frequency mixer MIX ₂ , and has a relatively narrow bandwidth. It is separately connected to the first frequency mixer MIX ₁ through a bandpass filter BPF having a filter.

By the way, both of the oscillators OSC ₁ and OSC ₂ mentioned above can be configured by a crystal oscillator, as an example, but it is not always necessary to use the oscillator OSC ₁ , as long as the reference input signal is obtained by an appropriate means. good. The first frequency mixer
A frequency modulator signal having the predetermined center frequency fo is output from MIX ₁ .

In addition, the output terminal of the self-oscillating frequency modulator FM is connected to a first frequency divider DV ₁ with a frequency division ratio of 1/n.
The output terminal of the oscillator OSC ₂ is connected to the phase detector PD via a frequency division ratio of 1/
It is connected to the phase detector PD via a second frequency mixer DV ₂ having a frequency of n.

Then, the phase detector PD compares the phases between the output signals of the first and second frequency dividers DV ₁ and DV ₂ , and this comparison output signal is fed back to the self-oscillation type frequency modulator FM, The output signal frequency fm of the self-oscillating frequency modulator FM is
Control to match the oscillation frequency fm of OSC ₂ .

[Function] Since the frequency modulation signal generating device of the present invention is configured as described above, it operates as follows, and the center frequency fo has high stability and the relevant signal is transmitted from the output terminal OUT. A frequency modulated signal having a center frequency output signal waveform having a sine wave is output.
In other words, the signal with the center frequency fm in the self-oscillating frequency modulator FM undergoes frequency modulation by a modulation signal such as an audio signal input from the input terminal IN.
Its output signal is guided to a first frequency mixer MIX ₁ . On the other hand, as an example, the reference input signal of frequency fo generated by the reference signal oscillator OSC ₁ and the oscillator
The signal of frequency fm from OSC ₂ is guided to the second frequency mixer MIX ₂ and frequency mixed, and the signal of frequency fm
This signal becomes the ±fo signal, and this signal is passed through the bandpass filter BPF.
It is separately led to a first frequency mixer MIX ₁ via.

Here, the bandpass filter BPF has its center frequency
fm+fo or fm-fo, and has a relatively narrow bandwidth, and this band filter BPF removes signals at frequencies fm and fm-fo or fm+fo, and also removes signals at frequencies 2(fm+fo) or 2(fm-fo). harmonic components of integer multiples, such as fo), are also removed. Note that, as described above, in the present invention, the frequencies have a relationship of fm≫fo. Therefore,
Since harmonic components as distortion components are removed from the output signal of the bandpass filter BPF, the output signal waveform becomes a sine wave and is guided to the first frequency mixer MIX ₁ .

Then, from this first frequency mixer MIX ₁ , the signal of frequency fm and the signal of frequency fm + fo or fm - fo are frequency mixed, with the center frequency being fo,
A frequency modulated signal whose output signal waveform itself is a sine wave at the center frequency is output from the output terminal UT, and a frequency modulated signal whose center frequency is an integral multiple of the center frequency fo, such as 2fo, is not output.

On the other hand, a part of the output signal from the self-oscillating frequency modulator FM is divided in frequency to fm/n via the first frequency divider DV ₁ and guided to the phase detector PD.

Also, part of the output signal from the oscillator OSC ₂ is also routed through the second frequency divider DV ₂ to have the same frequency.
The frequency is divided into fm/n and guided to the phase detector PD, which then compares the phase difference between the two signals, and a DC signal proportional to the phase difference is self-excited as a comparison output signal. Oscillation type frequency modulator
Returned to FM. Note that the reason why both signals input to the phase detector PD are frequency-divided to equalize their frequencies as described above is to perform phase detection of both signals.

Then, the output signal frequency from the self-oscillating frequency modulator FM is controlled to match the oscillation frequency fm from the oscillator OSC ₂ by the feedback detected DC signal. As a result, the first frequency mixer MIX ₁
The center frequency of the frequency modulated signal output from the oscilloscope is controlled so as to match the frequency fo of the reference input signal, thereby stabilizing the center frequency fo.

[Effects] As detailed above, according to the present invention, the output signal of the self-oscillating frequency modulator whose center frequency is higher than a predetermined center frequency is guided to the first frequency mixer, while , frequency-mixing an oscillation signal of an oscillator that generates a signal with a frequency equal to the center frequency of the self-oscillating frequency modulator and a reference frequency signal of the reference input signal by a second frequency mixer;
This mixed signal is guided to the first frequency mixer through a band filter whose center frequency is either the sum or difference frequency of the mixed signals, and from the first frequency mixer, A frequency modulated signal with a predetermined center frequency is output, and the bandpass filter is used to perform both signal frequency selection and harmonic removal as described above. The output signal of the frequency fo can itself be a sine wave, and a frequency modulation signal such as 2fo whose center frequency is an integral multiple of the center frequency fo has an extremely excellent effect of being able to make it a non-output signal. . Furthermore, even if a filter is attached to the outside of this device or incorporated in it to remove harmonic components such as 2fm, 2fm±fo, etc., the relationship of fm≫fo exists in the present invention. The filter characteristics may be extremely broad.

On the other hand, a part of the output signal of the self-oscillating frequency modulator itself and the output signal of the oscillator are respectively input to a phase detector via a frequency divider, and the detected output signal from this phase detector is is fed back to the self-excited oscillation type frequency modulator to control the output signal frequency of this self-excited oscillation type frequency modulator to be equal to the signal frequency generated by the oscillator, so that the center frequency of the frequency modulation signal output is used as the reference. It also exhibits an extremely excellent effect in that it can always be stabilized at an accurate value by matching the frequency of a predetermined reference signal in the input signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a frequency modulation signal generator according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional type. BPF...bandwidth filter, IN...input terminal,
DV ₁ , DV ₂ ...first and second frequency dividers,
FM...Self-oscillation frequency modulator, OUT...Output terminal, MIX ₁ , MIX ₂ ...First and second frequency mixer, OSC ₁ ...Reference signal oscillator, OSC ₂ ...Oscillator, PD... ...Phase detector.

Claims (1)

[Claims] 1 Connect the output terminal of a self-oscillating frequency modulator whose center frequency is a frequency (fm) in the relationship of fm≫fo with respect to a predetermined center frequency (fo) to one input terminal of the first frequency mixer. and, on the other hand, a reference signal with a frequency equal to the predetermined center frequency (fo) and a center frequency (fm) of the self-oscillating frequency modulator.
An oscillation signal from OSC ₂ that oscillates a signal with a frequency equal to connected to the other input terminal of the first frequency mixer via a bandpass filter whose center frequency is either the sum or difference frequency, and from the other input terminal to the first frequency mixer. The waveform of the input signal is a sine wave, and the first frequency mixer outputs a frequency modulated signal whose center frequency is the predetermined center frequency (fo) and whose waveform is a sine wave. A frequency modulation signal whose center frequency is at least twice the center frequency (fo) (2fo) is not outputted, and the output terminal of the self-oscillation type frequency modulator is separately connected via a first frequency divider. At the same time, the output terminal of the oscillator OSC ₂ is separately connected to the phase detector via a second frequency divider. The phases between the output signals of the frequency divider are compared, and this comparison output signal is fed back to the self-oscillation type frequency modulator to set the center frequency (fm) of the output signal of the self-oscillation type frequency modulator to the oscillator. A frequency modulation signal generator characterized by controlling the oscillation frequency to match the oscillation frequency of an OSC ₂ .