JPS63131706A - Frequency modulation circuit - Google Patents

Abstract

PURPOSE:To obtain a sinusoidal frequency modulation signal of object frequency by using a rectangular wave oscillation circuit, a frequency division circuit and a shift circuit so as to generate a 1st rectangular wave signal of an object frequency and a 2nd rectangular wave signal retarded by 1/6 period and adding the 1st and 2nd rectangular wave signals so as to eliminate harmonic com ponents. CONSTITUTION:A 3rd harmonic components S13, S23 included in the 1st rectan gular wave signal S1 and the 2nd rectangular wave signal S2 whose phase is retarded by 1/6 period with respect to the phase of the 1st rectangular wave signal S1 are dinusoidal waves whose phase differs by 1/2 period. Thus, in adding the 1st and 2nd rectangular wave signals S1, S2, the 3rd harmonic components S13, S23 included in the 1st and 2nd rectangular wave signals S1, S2 are canceled together to cancel the harmonic components.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Application Field The present invention relates to a frequency modulation circuit, and is suitable for application to a frequency modulation circuit used, for example, when recording a video signal on a magnetic tape in a video tape recorder (VTR). It is something.

B. Summary of the Invention The present invention provides a frequency modulation circuit that uses a rectangular wave oscillation circuit that oscillates a rectangular wave, a frequency divider circuit, and a shift circuit to generate a first rectangular wave signal of a target frequency and the first rectangular wave signal. By creating a second rectangular wave signal delayed by 1/6 cycle, and adding the first and second rectangular wave signals to remove the harmonic component, a frequency modulated signal of the target frequency consisting of a sine wave is obtained. get.

C. Prior Art In a video tape recorder (VTR), a carrier wave of a predetermined frequency is generally frequency-modulated (FM modulated) with a video signal and a signal is recorded on a magnetic tape. A heterodyne modulation circuit is used as the frequency modulation circuit.

However, this type of heterogain transformation circuit has problems in terms of stability and linearity, and a high-performance circuit that can solve these problems inevitably has a complicated circuit configuration.

For this reason, particularly in simple VTRs for consumer use, those that perform FM modulation using a variable frequency multi-vibration brake are used.

However, the output of this multivibrator-configured frequency modulation circuit is a rectangular wave signal, and therefore includes odd harmonic components. Among these, the third harmonic component in particular has a large level, and when the deviation of the fundamental wave component is wide, subcarriers may be mixed in, and even if the harmonic component is attenuated through a low-pass filter, it may fall within the band of the low-pass filter. However, there was a problem in that ripples in amplitude and ripples in group delay characteristics had an adverse effect.

Therefore, the first FM-modulated rectangular wave signal, the second rectangular wave signal whose phase is delayed by π/4 with respect to the first rectangular wave signal, and the second rectangular wave signal with respect to the second rectangular wave signal to create a third rectangular wave signal whose phase is delayed by π/4, and
and a frequency modulation circuit designed to reduce the third harmonic component of the third rectangular wave A δ is used (Japanese Patent Publication No. 60-4
Publication No. 8819).

D Problems to be Solved by the Invention However, in the frequency modulation circuit disclosed in Japanese Patent Publication No. 60-48819, in order to obtain the first, second, and third rectangular wave signals, a rectangular wave of a multivibrator configuration is used. The oscillation circuit is designed to oscillate a rectangular wave signal with a frequency four or nine times that of the target FME transmission. Wave frequency is approximately 20 (MHz)
Therefore, it is necessary to oscillate a rectangular wave signal of approximately 80 (MHz) or approximately 160 (M)Iz) in the rectangular wave oscillation circuit of the frequency modulation circuit. It is practically difficult to obtain.

The present invention has been made in consideration of the above problems, and attempts to solve the problems of conventional frequency modulation circuits at once and propose a frequency modulation circuit that can effectively remove harmonic components with a simple configuration. It is something to do.

E Means for Solving Problems In order to solve these problems, in the present invention, the frequency is shifted according to the input signal, a frequency twice the target frequency is obtained, and the duty ratio is 1:3. A rectangular wave oscillation circuit 2 that outputs a basic rectangular wave signal SB, and a rise t of the basic rectangular wave signal SB based on the basic rectangular wave signal SH.
Invert at Lt3, t5... and select the first target frequency.
A frequency dividing circuit that outputs a rectangular wave signal Sl, and a falling IQ of the basic rectangular wave signal SB based on the basic rectangular wave signal SB.
The second signal is inverted at t2, t4, t6... and whose phase is delayed by 1/6 period with respect to the first rectangular wave signal S1.
and a shift circuit 4 which outputs a rectangular wave signal S2 of The wave components S13 and S23 are removed.

2-action first rectangular wave signal Sl and a second rectangular wave signal S whose phase is delayed by 1/6 period with respect to the first rectangular wave signal Sl.
The third harmonic components S13 and S23 included in the second harmonic wave are sinusoidal waves whose phases differ from each other by 1/2 cycle.

This causes the first and second square wave signals, S L and S2
, the first and second rectangular wave signals Sl and S2
The third harmonic components S13 and S23 included in the signal cancel each other out and remove the high frequency component.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

1 and 2, reference numeral 1 designates a frequency modulation circuit as a whole, which is composed of a rectangular wave oscillation circuit 2, a frequency division circuit 3, a shift circuit 4, an addition circuit 5, and a low-pass filter 6.

The rectangular wave oscillation circuit 2 is composed of a multivibrator including a differential amplifier 2A, and uses charging and discharging of a capacitor connected to its non-inverting input terminal and inverting input terminal to convert the input video signal VD into a frequency. Modulate the target frequency 2
In addition to oscillating at twice the frequency, the R of the multivibrator
By selecting the C time constant as 1:2, a basic rectangle is created in which the rising width of the signal waveform of the output rectangular wave signal is 1/3 of one period (this is referred to as a duty ratio of 1=3). It is designed to output a wave signal SB (FIG. 2(A))- and its inverted basic rectangular wave signal (FIG. 2(B)).

Here, the video signal VD inputted to the middle point of the variable resistor VRIO of the rectangular wave oscillation circuit 2 is connected to the power supply VA via the first and second resistors R1 and R2, and the bases of the respective bases are connected to the power supply VA via the resistor R3. It is input to the emitters of the first and second transistors TRI and TR2, thereby configuring a voltage-dependent constant current circuit based on the video signal VD, and the collectors of each transistor TRI and TR2 are connected to the non-inverting input terminal of the differential amplifier 2Δ. Input to the inverting input terminal.

Further, the non-inverting output and the inverting output of the differential amplifier 2A are fed back to the non-inverting and inverting input terminals via feedback capacitors C1 and C2, respectively, and the non-inverting output and the inverting output are the basic square wave signal SB and the inverting output. It is applied to the clock input terminals CKI and CK2 of the frequency divider circuit 3 and shift circuit 4 as a basic rectangular wave signal (2).

Note that the capacitances of the feedback capacitors ct and C2 are selected to be C2-2C1, and the resistance values of the resistors R1 and R2 are selected to be equal.

Further, the variable resistor VR can be finely adjusted so that equal current flows through the non-inverting input side and the inverting input side, so that the duty ratio of the basic square wave signal SB outputted to the non-inverting output terminal is 1:3. It is done like this.

The frequency dividing circuit 3 consists of a 079217097 circuit, in which the basic square wave signal SB is input to the clock input terminal CKI, and outputs the first square wave signal S1 from the non-inverting output terminal Q1, and the first square wave signal S1 is obtained from the inverting output terminal. The inverted rectangular wave signal Sl is fed back to the data input terminal D1.

Here, the 079217097 circuit has a clock input terminal CK
When the input signal to I rises, based on the logic level value input to the data input terminal D1, the same logic level value is output to the non-inverting output terminal Q1, and at the same time, a value with an inverted logic level is inverted output. It is designed to output in 100 pieces.

That is, for example, as shown in FIG.
Immediately before the rising time t1, the first rectangular wave signal S
If 1 is a value of logic rLJ level, the inverted rectangular wave signal Sl is a value of logic rI(J level), and this is fed back to the data input terminal Di.

At time t1, which continues in this state, the basic square wave signal SB
rises to the logic rHJ level, the first square wave signal S1
, the logic rHJ level value of the inverted rectangular signal si input to the data input terminal D1 is output. Also, based on this, the inverted rectangular wave signal St is outputted at the logic rLJ level.

Further, the fundamental square wave signal SB becomes logic rL at time t2.
During the period t1 to t3 from falling to the J level and then rising again at time t3, the first rectangular wave signal S1 maintains the logic rHJ level value, and the inverted rectangular wave signal St is maintained at the logical rLJ level value.

Subsequently, at time t3, when the basic rectangular wave signal SB rises again, the first rectangular wave signal Sl outputs the value of the logic rLJ level of the inverted rectangular wave signal tone T input to the data input terminal D1. Ru. Based on this, one inverted rectangular wave signal is outputted as a logic rHJ level value.

As a result, the first rectangular wave signal S1 becomes the basic rectangular wave signal S
B rises at time t1. At t3, t5... (Fig. 2), the logic level is inverted, and thus the frequency is divided by 1/2 and the duty ratio is reduced compared to the basic square wave signal SB. The signal is a rectangular wave signal of l:2 (FIG. 2(C)).

Also, the shift circuit 4 is a D flip-flop circuit similar to the frequency divider circuit 3, and the inverted fundamental square wave signal ■ is inputted to the clock input terminal CK2, and the data input terminal DI of the frequency divider circuit 3 is inputted to the clock input terminal CK2.
An inverted rectangular wave signal Sl is connected to the data input terminal D2 connected to
is input manually, and a second rectangular wave signal S2 is obtained from the inverted output terminal (2).

As a result, the second rectangular wave signal S2 is generated at the times t2, t4, t6 when the inverted basic rectangular wave signal SB rises (therefore, the basic rectangular wave signal SB falls) similarly to the first rectangular wave signal S1.
... (FIG. 2), the logic level is inverted, thus with the same waveform as the first rectangular wave signal Sl, during periods t1 and t2, t3 and t4, t5 and t6.
A rectangular wave signal whose phase is delayed by a period of 1/6 period (π/3) with respect to the first rectangular wave signal S1 is obtained (FIG. 2(E)).

The adder circuit 5 is composed of, for example, a current adder circuit, and the frequency divider circuit 3
and the first and second rectangular wave signals S1 and S2 obtained by the shift circuit 4 to obtain a summed output signal SS.

Here, the first and second rectangular wave signals S1 and S2 include third harmonics S13 and S23 as shown in FIG. By shifting the phase of the rectangular wave signals Sl and S2 by π/3, each third
The phases of harmonics 513 and S23 are shifted from each other by π.

Therefore, among the signal components included in the addition output signal SS,
The third harmonics S13 and S23 cancel each other out, resulting in a signal that does not include the third harmonic.

Thus, by passing the addition output signal SS from which the third harmonic has been removed through the low-pass filter 6, which has a simple configuration and has a frequency band up to about 2.5 times the target frequency (that is, FMR transmission), the third harmonic is removed. 5 and higher harmonic components are removed, and a sinusoidal frequency modulation signal SFM consisting only of the FM carrier wave and subcarriers can be obtained.

Note that the basic rectangular wave signal SB output from the rectangular wave oscillation circuit 2 is actually frequency shifted by the video signal VD, but the first and second rectangular wave signals Sl and S2. Since the addition output signal SS and the frequency modulation signal SFM are similarly subject to frequency deviation, they are simplified in FIG. 2 and shown as not subject to deviation.

In the above configuration, first, the video signal VD input to the rectangular wave oscillation circuit 2 is frequency modulated into a basic rectangular wave signal SB having twice the frequency of the FM carrier wave of the target frequency and a duty ratio of 1=3. .

Subsequently, this basic rectangular wave signal SB is frequency-divided by 1/2 via the frequency divider circuit 3 to obtain a first rectangular wave signal S1 with a duty ratio of 1:2, and is then passed through the shift circuit 4 to obtain a first rectangular wave signal S1 with a duty ratio of 1:2. A second rectangular wave signal S2 delayed in phase by π/3 with respect to the first rectangular wave signal S1 is obtained.

Further, when the first and second rectangular wave signals S1 and S2 are added by the adder circuit 5, the phases of the third harmonics S13 and S23 contained therein differ by π, so that they cancel each other out, and the third harmonic Waves S13 and S23 are removed.

Thus, as the output of the low-pass filter 6, it is possible to obtain a sinusoidal frequency modulation signal SFM consisting only of the FMIII transmission wave of the target frequency and its subcarriers.

According to experiments, the frequency spectrum of the FM modulated wave by a conventional multi-by-break frequency modulation circuit has the following characteristics:
As shown in FIG.
Contains harmonic components 5fc and 5fsc.

On the other hand, according to the frequency modulation circuit 1 of the above-described embodiment, the frequency spectrum of the addition output signal SS of the addition circuit 5 has the third harmonic components 3f and 3, as shown in FIG.
f8. It shows a frequency distribution characteristic in which the rays are well removed.

As a result, as the low-pass filter 6, the FM carrier r,
If a filter having a filter characteristic TLPF that can pass frequencies up to about 2.5 times that of 5th harmonic components 5fc and 5f5 . can be effectively removed to obtain a frequency modulated signal SFM consisting only of the FMIII transmission wave fc and the subcarrier signals rsc distributed above and below it.

According to the above configuration, the RC time constant of the multi-by-break rectangular wave oscillation circuit is set to 1:2, and the duty ratio of the oscillated basic rectangular wave signal is set to 1:3. Since the oscillation frequency of the basic rectangular wave signal is 1/2 or 1/4 compared to the circuit, a rectangular wave oscillation circuit with a simple configuration can be used.

In addition, the frequency is shifted according to this input signal, and a simple configuration consisting of a D flip-flop circuit is based on a fundamental rectangular wave signal with a frequency twice the target frequency and a duty ratio of 1:3. create a first rectangular wave signal of the target frequency and a second rectangular wave signal whose phase is delayed by 1/6 cycle with respect to the first rectangular wave signal through the frequency divider circuit and shift circuit, By adding the first and second rectangular wave signals, each third wave signal included in the first and second rectangular wave signals is
The harmonic components cancel each other out and are effectively removed.

In this way, it is possible to realize a frequency modulation circuit that can effectively remove unnecessary harmonic components and obtain a frequency modulation signal consisting of a sine wave with an overall simple configuration.

In the above embodiment, an example in which the frequency modulation circuit according to the present invention is used in a VTR is shown, but the frequency modulation circuit according to the present invention is not limited to this, and can be widely applied to electronic equipment such as communication equipment. It's something you get.

H Effects of the Invention The present invention provides a frequency modulation circuit that uses a rectangular wave oscillation circuit that oscillates a rectangular wave that is twice the target frequency and has a duty ratio of 1:3, a frequency divider circuit, and a shift circuit. By creating a first rectangular wave signal and a second rectangular wave signal whose phase is delayed by 1/6 period with respect to the first rectangular wave signal, and adding these, harmonic components can be obtained well with a simple configuration. It is possible to realize a frequency modulation circuit that can remove the frequency modulation signal and obtain a frequency modulation signal of a target frequency consisting of a sine wave.

[Brief explanation of the drawing]

Fig. 1 is a connection diagram showing an embodiment of the frequency modulation circuit according to the present invention, Fig. 2 is a signal waveform diagram of each part thereof, and Fig. 3 is the frequency distribution of frequency modulated waves by a frequency modulation circuit with a conventional multivibrator configuration. FIG. 4 is a characteristic curve diagram showing the frequency distribution of frequency modulated waves in the frequency modulation circuit according to the present invention. 1... Frequency modulation rgJ path, 2... Rectangular wave oscillation circuit, 3... Frequency division circuit, 4...
・Shift circuit, 5... Addition circuit, 6...
・Low pass filter. 25 people 7f) No. 16 j skin gun [] Figure 2

Claims (1)

[Claims] A rectangular wave oscillation circuit that outputs a fundamental rectangular wave signal whose frequency is shifted according to an input signal, has a frequency twice the target frequency, and has a duty ratio of 1:3; a frequency dividing circuit that outputs a first rectangular wave signal of the target frequency by inverting the basic rectangular wave signal at the rising edge thereof based on the rectangular wave signal; is inverted at the falling edge of , and is 1 for the first rectangular wave signal.
a shift circuit that outputs a second rectangular wave signal whose phase is delayed by /6 cycles, and by adding the first and second rectangular wave signals, the first and second rectangular wave signals are A frequency modulation circuit characterized in that it removes contained harmonic components.