JPH08274661A - Fm wireless microphone - Google Patents

Abstract

PURPOSE: To provide the FM wireless microphone which can be integrated and has a simple constitution. CONSTITUTION: An oscillator 2 includes two phase shift circuits 10 and 30 and oscillates a sine wave having such frequency that the extent of phase sift of a signal making a round is 0 deg.. Especially, a capacitor microphone 34-2 is used as the capacitor of one phase shift circuit 30, and the change corresponding to the acoustic pressure of the electrostatic capacity of the capacitor microphone 34-2 is directly used for FM modulation, and an FM carrier is outputted from an antenna 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM wireless microphone for FM-modulating and transmitting voice.

[0002]

2. Description of the Related Art An FM wireless microphone amplifies the sound collected by a microphone and then performs FM modulation.
The modulated signal is amplified and transmitted from the antenna. Therefore, a microphone, a low frequency amplifier circuit, an F
It is configured to include an M modulation circuit, a high frequency amplifier circuit, and an antenna.

In the FM modulation circuit having such a structure, an LC oscillator which generates a sine wave with little distortion is generally used. As this LC oscillator, there are various kinds of oscillators such as Colpitts type. For example, the capacitor of the LC resonance circuit included therein is constituted by a varicap (variable capacitance diode), and its capacitance is changed in the voltage level of the audio output. F by changing the
M modulation is performed.

[0004]

By the way, the above-mentioned LC oscillator is generally used in the FM modulation circuit used in the above-mentioned conventional FM wireless microphone,
A large inductor (for example, about 100 nH) is used. Therefore, only the inductor has to be an external component, which makes integration difficult.

Further, various conventional LC oscillators are
If the oscillation frequency is changed significantly, the voltage level of the oscillation output also changes, which is not practical as it is. Therefore, when such an LC oscillator is used, a circuit that keeps the voltage level of the FM carrier constant is necessary, which complicates the configuration.

Therefore, the present invention was created in view of the above problems, and the purpose thereof is to enable FM integration.
To provide a wireless microphone. Another object of the present invention is to provide an FM wireless microphone having a simple circuit configuration.

[0007]

In order to solve the above-mentioned problems, an FM wireless microphone according to a first aspect of the present invention is a condenser microphone that collects voice, an oscillator to which the condenser microphone is connected, and an output from the oscillator. In the FM wireless microphone including an antenna for outputting a signal to the air, the oscillator includes a differential input amplifier having one end of a first resistor connected to an inverting input terminal, and an inverting input of the differential input amplifier. A second resistor connected between the terminal and the output terminal; and a series circuit including a third resistor and a capacitor connected to the other end of the first resistor, the third resistor and the Two phase shift circuits in which a connecting part of a capacitor is connected to a non-inverting input terminal of the differential input amplifier are provided, and an output of the phase shift circuit at a subsequent stage is fed back to an input side of the phase shift circuit at a previous stage. Together, by using the condenser microphone as said capacitor included in one of the two phase shifting circuits, and outputs an FM modulated signal from one of said two phase shifting circuits.

An FM wireless microphone according to a second aspect of the present invention includes a condenser microphone that collects voice, an oscillator to which the condenser microphone is connected, and an antenna that outputs a signal output from the oscillator to the air. In the oscillator, the oscillator includes a differential input amplifier having an inverting input terminal connected to one end of a first resistor, and a second resistor connected between the inverting input terminal and the output terminal of the differential input amplifier. And a third resistor connected to the other end of the first resistor.
And a series circuit composed of a resistor and a capacitor, the two phase shift circuits connecting the connection portion of the third resistor and the capacitor to the non-inverting input terminal of the differential input amplifier, and A non-inverting circuit that performs power amplification without changing the phase of the AC signal output from the phase-shifting circuit, and outputs the output of the non-inverting circuit to the input side of the phase-shifting circuit connected to the preceding stage. It is characterized by outputting the FM-modulated signal from the non-inverting circuit by feeding back and using the condenser microphone as the capacitor included in one of the two phase shift circuits.

An FM wireless microphone according to a third aspect of the present invention is the FM wireless microphone according to the first or second aspect, in which the connection method of the third resistor and the capacitor forming the series circuit is changed in the two phase shift circuits. Characterized by the opposite.

An FM wireless microphone according to a fourth aspect of the present invention includes a condenser microphone that collects sound, an oscillator to which the condenser microphone is connected, and an antenna that outputs a signal output from the oscillator to the air. In the oscillator, the oscillator includes a differential input amplifier having an inverting input terminal connected to one end of a first resistor, and a second resistor connected between the inverting input terminal and the output terminal of the differential input amplifier. And a third resistor connected to the other end of the first resistor.
And a series circuit composed of a resistor and a capacitor, the two phase shift circuits connecting the connection portion of the third resistor and the capacitor to the non-inverting input terminal of the differential input amplifier, and A phase inversion circuit that inverts the phase of the AC signal output from the phase shift circuit and outputs by performing power amplification and outputs the output of the phase inversion circuit to the input side of the phase shift circuit connected to the preceding stage. In addition to the feedback, the condenser microphone is used as the capacitor included in one of the two phase shift circuits to output an FM-modulated signal from the phase inversion circuit.

An FM wireless microphone according to a fifth aspect of the present invention is the FM wireless microphone according to the fourth aspect, wherein the connection method of the third resistor and the capacitor forming the series circuit is the same in the two phase shift circuits. It is characterized by having done.

An FM wireless microphone according to a sixth aspect is the FM wireless microphone according to any one of the first to fifth aspects,
The differential input amplifier is an operational amplifier.

An FM wireless microphone according to a seventh aspect is the FM wireless microphone according to any one of the first to sixth aspects,
A capacitor having a fixed electrostatic capacitance is connected in series or in parallel with the condenser microphone.

An FM wireless microphone according to claim 8 is the FM wireless microphone according to any one of claims 1 to 7, wherein
The third resistor included in at least one of the two phase shift circuits is a variable resistor.

An FM wireless microphone according to a ninth aspect is the FM wireless microphone according to the eighth aspect, characterized in that the variable resistance is formed by a channel of a field effect transistor, and a channel voltage is changed by changing a gate voltage.

An FM wireless microphone according to a tenth aspect is the FM wireless microphone according to the eighth aspect, in which the variable resistor is formed by connecting a p-channel type field effect transistor and an n-channel type field effect transistor in parallel. The channel resistance is changed by changing the magnitude of the gate voltage of each field effect transistor having different polarities.

An FM wireless microphone according to claim 11 is the FM wireless microphone according to any one of claims 1 to 7, wherein the capacitor included in at least one of the two phase shift circuits is a variable capacitance element. To do.

An FM wireless microphone according to a twelfth aspect is the FM wireless microphone according to any one of the first to seventh aspects, in which the resistance value is fixed as the third resistor included in at least one of the two phase shift circuits. It has a resistance of 1 and is selectively connected by switching a switch.

An FM wireless microphone according to a thirteenth aspect is the FM wireless microphone according to any one of the first to seventh aspects, wherein the capacitors included in at least one of the two phase shift circuits have a plurality of fixed capacitances. It is characterized by being selectively connected by switching a switch.

An FM wireless microphone according to a fourteenth aspect is the FM wireless microphone according to any one of the first to thirteenth aspects, wherein each component of the oscillator is integrally formed on a semiconductor substrate.

[0021]

According to the inventions of claims 1 to 3, the oscillator includes two phase shift circuits using a condenser microphone as one of the capacitors, and the signal output from the phase shift circuit in the subsequent stage is directly or It is fed back to the input side of the preceding phase shift circuit via the non-inverting circuit. In each phase shift circuit, only the phase is shifted without attenuating the amplitude of the input signal, and the two phase shift circuits perform sine wave oscillation at a frequency at which the total phase shift amount is 0 °. In particular, since one of the capacitors is composed of a condenser microphone, the capacitance of this condenser microphone changes according to the volume of the collected voice, and an FM-modulated signal can be easily obtained.

According to the present invention, the FM modulation can be directly performed by utilizing the change of the electrostatic capacity of the condenser microphone, and an additional circuit for converting the change of the electrostatic capacity into the change of the voltage once is provided. Since it is unnecessary, the circuit configuration of the entire FM wireless microphone can be simplified. Further, since sinusoidal wave oscillation is performed without using an inductor or the like, integration can be easily performed on the semiconductor substrate.

Similarly, in the invention of claim 4 or 5, the oscillator is configured to include two phase shift circuits using a capacitor microphone as one of the capacitors and a phase inversion circuit, and output from the phase inversion circuit. This signal is fed back to the input side of the phase shift circuit in the previous stage. In each phase shift circuit, only the phase is shifted without attenuating the amplitude of the input signal, and the two phase shift circuits and the phase inversion circuit are sinusoidal at a frequency at which the total amount of phase shift is 0 °. Oscillation is performed. In particular, since one of the capacitors is composed of a condenser microphone, the capacitance of this condenser microphone changes according to the volume of the collected voice, and an FM-modulated signal can be easily obtained.

According to the invention of claim 4 or 5, the FM modulation can be directly performed by utilizing the change of the electrostatic capacity of the condenser microphone, and an additional circuit for converting the change of the electrostatic capacity into the change of the voltage once is provided. Since it is unnecessary, the circuit configuration of the entire FM wireless microphone can be simplified. Further, since sinusoidal wave oscillation is performed without using an inductor or the like, integration can be easily performed on the semiconductor substrate.

In the sixth aspect of the invention, the differential input amplifier included in the phase shift circuit is specifically configured by an operational amplifier, so that the stability of the entire circuit can be increased.

Further, in the invention of claim 7, instead of using the condenser microphone itself as a capacitor, it is combined with a capacitor having a fixed capacitance. Therefore, it is possible to arbitrarily adjust the ratio of the change in the capacitance of the condenser microphone to the change in the overall capacitance after the combination according to the combination method and the capacitance of the combined capacitors. The modulation degree can be easily adjusted.

According to the present invention, the resistance value of the third resistor included in the phase shift circuit in the oscillator is changed, specifically, a variable resistor is formed by the FET to form a channel. Since the amount of phase shift in the phase shift circuit changes by changing the resistance, the frequency of the FM carrier to be transmitted can be changed arbitrarily.

In particular, when the variable resistance is formed by the FET, the non-linear region of the FET can be improved by using the p-channel FET and the n-channel FET connected in parallel, and the harmonic component can be reduced. The FM carrier with less distortion can be transmitted.

According to the invention of claim 11, instead of using a variable resistor, a capacitor is formed by a variable capacitance element to change the amount of phase shift in the phase shift circuit, thereby changing the frequency of the FM carrier to be transmitted. It can be changed arbitrarily.

According to the invention of claim 12 or 13,
Instead of using an element whose element constant itself is variable, such as a variable resistor or variable capacitance element, prepare multiple elements with different element constants as resistors and capacitors and select one of them by switching the switch. Alternatively, a plurality of arbitrary elements are used in combination. Therefore, the frequency of the FM-modulated signal can be changed discontinuously. For example, it is suitable for preparing a plurality of frequencies to avoid interference.

According to the fourteenth aspect of the invention, the entire oscillator is integrally formed on the semiconductor substrate, and it is possible to reduce the size of the circuit and reduce the manufacturing cost by integration.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An FM wireless microphone according to an embodiment of the present invention will be specifically described below with reference to the drawings.

(First Embodiment) FIG. 1 is a diagram showing the configuration of an FM wireless microphone according to the first embodiment of the present invention.

The FM wireless microphone of this embodiment shown in FIG. 1 includes an antenna 1 for transmitting an FM carrier and an oscillator 2 for supplying an FM-modulated signal to the antenna 1.
It is comprised including. The FM wireless microphone shown in FIG. 1 shows only a basic circuit configuration. For example, when it is desired to increase the transmission output, a power amplification circuit may be inserted between the oscillator 2 and the antenna 1. .

The above-mentioned oscillator 2 includes two phase shift circuits 1 each of which performs a phase shift of 0 ° in total at a predetermined frequency by shifting the phase of the input signal by a predetermined amount.
0 and 30, and a feedback resistor 70 for feeding back the output of the phase shift circuit 30 in the subsequent stage to the input side of the phase shift circuit 10 in the previous stage. The feedback resistor 70 has a finite resistance value from 0Ω.

FIG. 2 shows the phase shift circuit 10 of the preceding stage shown in FIG.
The configuration of is extracted and shown. The phase shift circuit 10 at the front stage shown in FIG. 1 includes an operational amplifier (operational amplifier) 12 which is a kind of differential input amplifier, and a non-inverting input of the operational amplifier 12 by shifting a phase of a signal input to an input end 22 by a predetermined amount. A capacitor 14 and a resistor 16 input to the terminals, a resistor 18 inserted between the input end 22 and the inverting input terminal of the operational amplifier 12, and a resistor inserted between the output end 24 of the operational amplifier 12 and the inverting input terminal. 20 and 20 are included.

In this specification, it is assumed that the operational amplifier 12 and the like operate ideally, and when deviation from the ideal is a problem when actually designing a circuit, description will be added each time. .

In the phase shift circuit 10 having such a configuration, when a predetermined AC signal is input to the input end 22, the voltage VR1 appearing across the resistor 16 is applied to the non-inverting input terminal of the operational amplifier 12. It

Further, since there is no potential difference between the two inputs (the inverting input terminal and the non-inverting input terminal) of the operational amplifier 12 shown in FIG. 2, the potential of the inverting input terminal of the operational amplifier 12 and
The potential at the connection point between the capacitor 14 and the resistor 16 becomes equal. Therefore, the capacitor 14 is connected to both ends of the resistor 18.
A voltage VC1 that is the same as the voltage VC1 that appears across both ends of the.

Here, assuming that the resistance values of the resistor 18 and the resistor 20 are equal, the same current flows through these two resistors 18 and 20, so that the voltage VC1 also appears at both ends of the resistor 20. Moreover, the voltages VC1 appearing at both ends of these two resistors 18 and 20 have the same vector direction, and considering the inverting input terminal (voltage VR1) of the operational amplifier 12 as a reference, the voltage at both ends of the resistor 18 is considered. The vector addition of VC1 is the input voltage Ei, and the vector subtraction of the voltage VC1 of the resistor 20 is the output voltage Eo.

FIG. 3 is a vector diagram showing the relationship between the input / output voltage of the phase shift circuit 10 and the voltage appearing at the capacitor or the like.

As shown in the figure, the voltage VR1 appearing across the resistor 16 and the voltage VC1 appearing across the capacitor 14 are 90 ° out of phase with each other, and the vector addition of these results in the input voltage Ei. Becomes Therefore, when the amplitude of the input signal is constant and only the frequency changes,
Along the circumference of the semicircle shown in FIG.
And the voltage VC1 across the capacitor 14 change.

The output voltage Eo is obtained by subtracting the voltage VC1 from the voltage VR1 in vector. Considering the voltage VR1 applied to the non-inverting input terminal as a reference, the input voltage Ei
The output voltage Eo differs from the output voltage Eo only in the direction in which the voltage VC1 is combined, and their absolute values are equal. Therefore, the relationship between the magnitude and the phase of the input / output voltage can be expressed by an isosceles triangle whose hypotenuse is the input voltage Ei and output voltage Eo and whose base is twice the voltage VC1, and the amplitude of the output signal is related to the frequency. It can be seen that the amplitude is the same as that of the input signal and the phase shift amount is represented by φ1 shown in FIG.

As is clear from FIG. 3, the voltage VR1
And the voltage VC1 intersect at a right angle on the circumference, theoretically, the phase difference between the input voltage Ei and the voltage VR1 changes from 90 ° to 0 ° as the frequency ω changes from 0 to ∞. The phase shift amount φ1 of the entire phase shift circuit 10 is twice that, and changes from 180 ° to 0 ° depending on the frequency.

Next, the relationship between the input and output voltages described above will be quantitatively verified.

When the input voltage Ei is applied to the input end 22, the current flowing through the resistors 18 and 20 from the input end 22 to the output end 24 is I, and the resistance values of the resistors 18 and 20 are equal. Is r, the voltage across each of the resistors 18 and 20 is −I · r.

By the way, as described above, since no potential difference should occur between the two inputs (the inverting input terminal and the non-inverting input terminal) of the operational amplifier 12 shown in FIG. 2, it is applied to the non-inverting input terminal of the operational amplifier 12. Between the voltage VR1 across the resistor 16 and the output voltage Eo

[Equation 1] There is a relationship.

Further, in order to prevent a potential difference between the two inputs of the operational amplifier 12, the value obtained by adding the voltage VC1 across the capacitor 14 and the voltage −I · r across the resistor 18 must be 0.

[Equation 2] Becomes From equation (1) and equation (2),

(Equation 3) Becomes

Further, the sum of the voltages VR1 and VC1 across the resistor 16 and the capacitor 14 is the voltage Ei applied to the input terminal 22, so that between these voltages,

[Equation 4] There is a relationship. From equations (3) and (4),

(Equation 5) Becomes Here, C is the capacitance of the capacitor 14, R is the resistance value of the resistor 16, and the time constant of the CR circuit is T (= C
R).

Substituting s = jω in the equation (5) and transforming it,

(Equation 6) Becomes When the absolute value of the output voltage Eo is calculated from the equation (6),

(Equation 7) Becomes That is, the expression (7) is obtained by the phase shift circuit 1 of the present embodiment.
The value 0 indicates that the amplitude of the output signal is equal to the amplitude of the input signal and is constant no matter how the phase between the input and the output is rotated.

Further, when the phase shift amount φ1 of the output voltage Eo with respect to the input voltage Ei is calculated from the equation (6),

(Equation 8) Becomes From this equation (8), for example, ω is approximately 1 / T (=
The phase shift amount φ1 at a frequency that becomes 1 / (CR) becomes approximately 90 °, and only the phase can be shifted by approximately 90 ° without attenuating the amplitude of the input signal.

FIG. 4 shows the phase shift circuit 30 at the rear stage shown in FIG.
The configuration of is extracted and shown. Note that, in FIG. 4, the entire capacitor 34-1 and the capacitor microphone 34-2 in the phase shift circuit 30 in the latter stage shown in FIG. 1 are replaced by one equivalent capacitor 34.

The subsequent phase shift circuit 30 shown in FIG. 4 is an operational amplifier 32, which is a kind of differential input amplifier, and a non-inverting input terminal of the operational amplifier 32 by shifting the phase of the signal input to the input end 42 by a predetermined amount. To the resistor 36 and the above-mentioned capacitor 34, the resistor 38 inserted between the input end 42 and the inverting input terminal of the operational amplifier 32, and the resistor 38 inserted between the output end 44 of the operational amplifier 32 and the inverting input terminal. The resistor 40 is included.

In the phase shift circuit 30 having such a configuration, when a predetermined AC signal is input to the input end 42, the voltage VC2 appearing across the capacitor 34 is applied to the non-inverting input terminal of the operational amplifier 32. It

Further, since there is no potential difference between the two inputs (the inverting input terminal and the non-inverting input terminal) of the operational amplifier 32 shown in FIG. 4, the potential of the inverting input terminal of the operational amplifier 32,
The potential at the connection point between the resistor 36 and the capacitor 34 becomes equal. Therefore, the same voltage VR2 that appears across the resistor 36 appears across the resistor 38.

Here, assuming that the resistance values of the resistor 38 and the resistor 40 are equal, the same current flows through these two resistors 38 and 40, so that the voltage VR2 also appears across the resistor 40. In addition, the voltages VR2 appearing at both ends of these two resistors 38 and 40 are vector-oriented in the same direction, and considering the inverting input terminal (voltage VC2) of the operational amplifier 32 as a reference, the voltage VR2 at both ends of the resistor 38 is taken into consideration. Is added vectorically to the input voltage Ei, and the voltage R2 across the resistor 40 is vectorically subtracted to become the output voltage Eo.

FIG. 5 is a vector diagram showing the relationship between the input / output voltage of the subsequent phase shift circuit 30 and the voltage appearing at the capacitor or the like.

As shown in the figure, the voltage VC2 appearing across the capacitor 34 and the voltage VR2 appearing across the resistor 36 are 90 ° out of phase with each other, and the vector addition of these results in the input voltage Ei. Becomes Therefore, when the amplitude of the input signal is constant and only the frequency changes,
The voltage VC2 across the capacitor 34 and the voltage VR2 across the resistor 36 change along the circumference of the semicircle shown in FIG.

Further, as described above, the voltage VC2 to the voltage V
The output voltage Eo is obtained by subtracting R2 in vector.
Considering the voltage VC2 applied to the non-inverting input terminal as a reference, the input voltage Ei and the output voltage Eo differ only in the direction in which the voltage VR2 is combined, and their absolute values are equal. Therefore, the relationship between the magnitude and phase of the input / output voltage can be expressed by an isosceles triangle whose hypotenuse is the input voltage Ei and output voltage Eo and whose base is twice the voltage VR2, and the amplitude of the output signal is related to the frequency. It can be seen that the amplitude is the same as that of the input signal and the phase shift amount is represented by φ 2 shown in FIG.

As is clear from FIG. 5, the voltage VC2
And the voltage VR2 intersect at a right angle on the circumference, theoretically, the phase difference between the input voltage Ei and the voltage VC2 changes from 0 ° to 90 ° as the frequency ω changes from 0 to ∞. The shift amount φ2 of the entire phase shift circuit 10a is twice that, and changes from 0 ° to 180 ° depending on the frequency.

Next, the relationship between the input and output voltages described above will be verified quantitatively.

As in the case of the phase shift circuit 10 in the preceding stage, when the voltage Ei is applied to the input end 42, the current flowing from the input end 42 to the output end 44 through the resistors 38 and 40 is I, the resistance 38. And the resistance value of the resistor 40 are equal and the value is r
Then, the voltage across each of the resistors 38 and 40 is -I.
・ It becomes r.

Since there must be no potential difference between the two inputs (the inverting input terminal and the non-inverting input terminal) of the operational amplifier 32 shown in FIG. 4, the voltage across the capacitor 34 applied to the non-inverting input terminal of the operational amplifier 32. Between VC2 and the output voltage Eo,

[Equation 9] There is a relationship.

In order to prevent a potential difference between the two inputs of the operational amplifier 32, the voltage VR2 across the resistor 36 and the resistor 3 are applied.
Since the value obtained by adding the voltage −I · r across both ends of 8 must be 0,

[Equation 10] Becomes From equations (9) and (10),

[Equation 11] Becomes

Further, the sum of the voltages VC2 and VR2 across the capacitor 34 and the resistor 36 is the voltage Ei applied to the input terminal 42, so that between these voltages,

(Equation 12) There is a relationship. From equations (11) and (12),

(Equation 13) Becomes Here, C represents the electrostatic capacitance of the capacitor 34, R represents the resistance value of the resistor 36, and the time constant of the CR circuit is T (= CR) as in the case of the phase shift circuit 10 in the previous stage.

Substituting s = jω in the equation (13) and transforming it,

[Equation 14] Becomes

The above equations (13) and (14) are
Only the symbols are different from the equations (5) and (6) shown for the phase shift circuit 10 in the previous stage. Therefore, as for the absolute value of the output voltage Eo, the equation (7) can be applied as it is, and no matter how the phase between the input and the output of the phase shift circuit 30 in the subsequent stage is rotated, the amplitude of the output signal is the input signal. It can be seen that the amplitude is equal to and constant.

Further, when the phase shift amount φ2 of the output voltage Eo with respect to the input voltage Ei is obtained from the equation (14),

(Equation 15) Becomes From this equation (15), for example, ω is approximately 1 / T
The phase shift amount φ2 at a frequency such that (= 1 / (CR)) is approximately 90 °, and only the phase can be shifted by approximately 90 ° without attenuating the amplitude of the input signal.

By the way, a general condenser microphone 34-
Reference numeral 2 is a microphone that utilizes a change in electrostatic capacitance of a parallel plate capacitor, and a predetermined DC voltage is applied between parallel electrodes through a resistance of several tens of MΩ to respond to a change in electrostatic capacitance due to sound pressure. The voltage change is extracted as an electric signal. Therefore, in the normal use, it is necessary to apply a predetermined DC voltage, but in the present embodiment, the capacitor microphone 3 is used as a capacitor whose capacitance changes according to the sound pressure.
Since 4-2 is used, it is not necessary to apply a predetermined DC voltage.

As described above, since both the capacitor 34-1 and the capacitor microphone 34-2 are capacitors and can be replaced by the single capacitor 34 shown in FIG. 4, the phase shift circuit 30 is basically It has the same configuration as the phase shift circuit 10. Therefore, the entire capacitor 34-1 and the condenser microphone 34-2 are combined into one capacitor 34.
If the electrostatic capacity is considered to be C, the phase shift circuit 30
Has a phase shift amount φ2 as expressed by the above equation (15). Therefore, for example, ω is approximately 1 / T
The amount of phase shift φ2 at the frequency
It becomes 0 °.

In this way, the two phase shift circuits 10, 3
At each 0, the phase is shifted by a predetermined amount. Moreover, as shown in FIGS. 3 and 5, each of the phase shift circuits 10, 3
The relative phase relationship of the input and output voltages at 0 is in the opposite direction, and the two phase shift circuits 10 and 3 at a predetermined frequency.
A signal in which the total of the phase shift amounts is 0 ° is output by the total of 0.

Moreover, the output of the phase shift circuit 30 in the subsequent stage is fed back to the input side of the phase shift circuit 10 via the feedback resistor 70, and the loop gain is set to be larger than 1 so that the phase shifts once when the loop is completed. Sine wave oscillation is performed at a frequency such that the shift amount is 0 °.

FIG. 6 is a system diagram in which the entire two phase shift circuits 10 and 30 having the above-mentioned configuration are replaced with a circuit having a transfer function K1. The circuit having the transfer function K1 and the feedback resistor having the resistance value R0 are shown in FIG. 70 and 70 form a closed loop. FIG. 7 is a system diagram in which the system shown in FIG. 6 is converted by the Miller's theorem. When the feedback resistor 70 having a resistance value R0 is converted into an input shunt resistance as shown in FIG.

[Equation 16] Can be represented by

In this equation, considering that K1 is larger than 1, it can be seen that the input shunt resistance Rs becomes a negative resistance.

Assuming that an ideal phase shift circuit (all-pass network) having a transfer function K1 satisfies the condition that the phase shift amount is 0 ° at an arbitrary finite frequency, it is selective at this frequency. A negative resistance will be realized and oscillation will be possible. Actually, the input shunt resistance is in the form of being connected in parallel with the input impedance of the phase shift circuit, and it is necessary that a composite of these is a negative resistance, but the resistance value R0 of the feedback resistance 70 is set low, Since it is extremely easy to set the input impedance of the phase shift circuit to be high, it is theoretically possible to ignore the influence of the input impedance of the phase shift circuit.

By the way, as is clear from the equation (5),
The transfer function K2 of the phase shift circuit 10 at the previous stage is

[Equation 17] As is clear from the equation (13), the transfer function K3 of the phase shift circuit 30 in the subsequent stage is

(Equation 18) Is. However, it is assumed that the time constants of the CR circuits in the phase shift circuits 10 and 30 are different, and T ₁ and T ₂ are respectively set.
And

Therefore, when the phase shift circuits 10 and 30 are cascaded in two stages, the overall transfer function K1 is

[Formula 19] Becomes Here, in order to simplify the calculation, s = jω,
s ² = −ω ² , A = 1 + T ₁ T ₂ s ² = 1−T ₁ T ₂ ω
² , B = T ₁ + T ₂

(Equation 20) Becomes In this equation (20), the phase shift circuits 10, 30
Since the imaginary number term on the right side of the equation (20) must be 0 in order for the phase difference between the input and output of the entire two-stage connected to become 0 °, the following equation holds.

[0078]

[Equation 21] Therefore, 1-T ₁ T ₂ ω ² = 0 or ω = 0. Here, when ω = 0, the input signal is DC and the phase difference is 180 °, so that the other condition (1
Ω = 1 / √ (T ₁ T ₂ ) satisfying −T ₁ T ₂ ω ² = 0)
At this time, the phase difference becomes 0 °. At this frequency, the input shunt resistance Rs becomes a negative resistance and simultaneously satisfies the oscillation voltage condition and the frequency condition.

When the operational amplifiers 12 and 32 operate ideally, the gain of the phase shift circuit 10 becomes 1 when the resistance values of the resistors 18 and 20 are equal to each other, and the resistance 38.
The gain of the phase shift circuit 30 becomes 1 when the resistance values of 40 and 40 are equal. However, in reality, there is a deviation from the ideal, and the gain in each phase shift circuit is 1 or less. Therefore, by setting the resistance value of the resistor 20 in the preceding phase shift circuit 10 to be larger than the resistance value of the resistor 18. Alternatively, by setting the resistance value of the resistor 40 in the subsequent phase shift circuit 30 to be larger than the resistance value of the resistor 38, the overall loop gain is set to 1
It should be set larger.

As described above, by combining the two phase shift circuits 10 and 30, the phase shift amount of the signal that goes through the closed loop can be made 0 ° at a certain frequency, and the loop gain at this time is larger than 1. By doing so, the sine wave oscillation is sustained. Moreover, the capacitance of the condenser microphone 34-2 connected to the second-stage phase shift circuit 30 changes according to the sound pressure, and the amount of phase shift in the phase shift circuit 30 also changes according to the sound pressure. Therefore, it is possible to directly generate an FM-modulated signal from voice and output it from the output terminal 92. The FM-modulated signal output from the output terminal 92 is emitted from the antenna 1 into the air.

As described above, in the FM wireless microphone of this embodiment, the change in the capacitance of the condenser microphone 34-2 is directly used for FM modulation, and the circuit structure can be simplified. In particular, compared to the conventional FM wireless microphone that amplifies the output of the condenser microphone and creates the reverse bias voltage applied to the varicap, the configuration for creating this reverse bias voltage is not required, and the circuit configuration is correspondingly simpler. Becomes

Further, in the FM wireless microphone of this embodiment, since the oscillator 2 is composed of only the operational amplifier, the resistor and the capacitor, and no inductor is used,
It is suitable for integration of the entire circuit except the condenser microphone 34-2. Moreover, since the inductor is not used, it is not necessary to take measures such as magnetic shielding.

In the FM wireless microphone of this embodiment, the condenser microphone is connected to the second-stage phase shift circuit 30, but the condenser microphone may be connected to the first-stage phase shift circuit 10.

FIG. 8 is a diagram showing a modification of the oscillator included in the FM wireless microphone of this embodiment. The oscillator 2a shown in the figure replaces the entire capacitor 34-1 and capacitor microphone 34-2 in the phase shift circuit 30 of the latter stage shown in FIG. 1 with the capacitor 34a having a fixed capacitance, and the phase shift circuit 30a of the latter stage. In addition to the above, the capacitor 14 in the phase shift circuit 10 in the preceding stage shown in FIG. 1 is replaced with a capacitor 14a-1 and a condenser microphone 34a-2 having a fixed capacitance to configure the phase shift circuit 10a in the preceding stage. is there.
The operations of the two phase shift circuits 10a and 30a are basically the same as those of the phase shift circuits 10 and 30 shown in FIG.
Condenser microphone 1 connected to the phase shift circuit 10a in the previous stage
The FM carrier is sent out from the antenna 1 by directly utilizing the change in the electrostatic capacity of 4a-2 for FM modulation.

Further, the total of the phase shift amounts is 0 by the whole of the two phase shift circuits 10, 30 or 10a, 30a.
Therefore, the phase shift circuit 10 in the previous stage in FIG.
And the front and rear arrangements of the phase shift circuit 30 in the rear stage and the phase shift circuit 30 in the rear stage in FIG.
You may make it replace the arrangement | positioning before and behind a.

The oscillator 2 used in the FM wireless microphone of the first embodiment described above is composed of two phase shift circuits 1.
The phase shift amount is 0 ° as a whole of 0 and 30 and a predetermined oscillation operation is performed, and a non-inverting circuit that performs power amplification without changing the phase may be added.

FIG. 9 shows the configuration of the FM wireless microphone of the first embodiment shown in FIG. 1 having the oscillator 2b in which the non-inverting circuit 50 described above is added to the next stage of the phase shift circuit 30. It is a figure. The non-inverting circuit 50 has an inverting input terminal grounded via a resistor 54 and a resistor 5 between the inverting input terminal and the output terminal.
6 is connected to the operational amplifier 52 and has a predetermined amplification degree determined by the resistance ratio of the two resistors 54 and 56.

The non-inverting circuit 50 having such a configuration.
Outputs without changing the phase of the input signal, and it is easy to set the loop gain to be larger than 1 by adjusting the amplification degree. Further, by performing power amplification by the non-inverting circuit 50, the F transmitted from the antenna 1 to the air is transmitted.
The output of M carrier can be increased.

Similarly, in the oscillator 2a shown in FIG. 8, the non-inverting circuit 50 described above is added to the next stage of the phase shift circuit 30a, or the two phase shift circuits of the oscillator shown in FIG. 1 or 8 are exchanged. At the same time, the above-described non-inverting circuit 50 may be added to the subsequent stage of the subsequent phase shift circuit.

(Second Embodiment) The FM of the first embodiment described above.
Although the oscillators 2 and 2a included in the wireless microphone are configured by combining the two phase shift circuits 10 and 30 having different configurations, the oscillator may be configured by combining two phase shift circuits having the same configuration. Good.

One of the phase shift circuits 10 and 10a included in the oscillator shown in FIG. 1 or FIG. 8 has the basic configuration shown in FIG. 2, and is arranged between the input and output of the phase shift circuits 10 and 10a. Satisfies the relationship expressed by equation (5). Hereinafter, the phase shift circuit 10 and the like having the configuration shown in FIG. 2 will be described as "-type phase shift circuit" for convenience, using the sign of the fraction in the expression (5). Further, the other phase shift circuit 30, 30a included in the oscillator shown in FIG. 1 or FIG. 8 has the basic configuration shown in FIG. 4, and between the input and output of the phase shift circuit 30, 30a. The relationship expressed by the equation (13) is established. In the following, the phase shift circuit 30 having the configuration shown in FIG.
For convenience sake, description will be given by using the sign of the fraction in the formula, and calling it "+ type phase shift circuit".

When the phase shift circuits are classified into two types for convenience as described above, the oscillators 2 and 2a included in the FM wireless microphone of the first embodiment have two phase shift circuits 10 and 30 of different types. By combining
The oscillation operation is performed at a frequency where the phase shift amount as a whole is 0 °.

By the way, when attention is paid to the relationship between the entire input and output when a phase inverting circuit for inverting the phase of a signal is connected to the subsequent stage of the one − type phase shift circuit 10, in the equation (5) It is sufficient to invert the sign “−” to “+”, and it can be said that the configuration in which the phase inversion circuit is connected to the subsequent stage of one − type phase shift circuit is equivalent to one + type phase shift circuit. Similarly, paying attention to the relationship between the entire input and output when a phase inversion circuit that inverts the phase of a signal is connected to the subsequent stage of one + type phase shift circuit 30, the sign of the fraction " It is sufficient to invert "+" to "-", and it can be said that the configuration in which the phase inversion circuit is connected to the subsequent stage of one + -type phase shift circuit is equivalent to one-type phase-shift circuit.

Therefore, instead of combining two phase shift circuits 10 and 30 of different types in the first embodiment to form an oscillator, two phase shift circuits of the same type and a phase inversion circuit are combined to form an oscillator. be able to.

FIG. 10 is a diagram showing the structure of the FM wireless microphone of the second embodiment, showing the detailed structure of the oscillator 2c.

The oscillator 2c shown in FIG.
2 type-shifting circuits 10 and 10a, and a phase inverting circuit 80 for further inverting the phases of the output signals of the subsequent phase shifting circuit 10a and performing power amplification, and a phase inverting circuit 8
A feedback resistor 70 for feeding back the output of 0 to the input side of the phase shift circuit 10 at the previous stage is included.

In the phase inversion circuit 80, the input signal is the resistance 84
An operational amplifier 82 that is input to the inverting input terminal via the and the non-inverting input terminal is grounded;
A resistor 8 connected between the inverting input terminal 2 and the output terminal
And 6 are included. When an AC signal is input to the inverting input terminal of the operational amplifier 82 via the resistor 84, a reverse-phase signal whose phase has been inverted is output from the output terminal of the operational amplifier 82. In addition, the phase inversion circuit 80
It has a predetermined amplification degree determined by the resistance ratio of the two resistors 84 and 86.

The phase inversion circuit 80 having such a configuration.
Makes it easy to invert the phase of the input signal and adjust the amplification factor to set the loop gain of the oscillator 2c to be larger than 1. Further, by performing power amplification by the phase inversion circuit 80, it is possible to increase the output of the FM carrier transmitted from the antenna 1 to the air.

By the way, as described in the above-mentioned first embodiment, each of the − type two phase shift circuits 10 and 10a has a phase shift amount as the frequency ω of the input signal changes from 0 to ∞. It changes from 180 ° to 0 °.
For example, assuming that the time constants of the CR circuits in the two phase shift circuits 10 and 10a are the same, and letting this be T, ω = 1
At the frequency of / T, the amount of phase shift in each of the two phase shift circuits 10 and 10a is 90 °. Therefore,
The phase is shifted by 180 ° by the two phase shift circuits 10 and 10a, and the phase is inverted by the phase inversion circuit 80 connected to the subsequent stage, so that the signal whose phase makes one round and the shift amount becomes 0 ° is the phase. It is output from the inverting circuit 80. Therefore, by feeding back the output of the phase inversion circuit 80 to the input side of the phase shift circuit 10 at the previous stage via the feedback resistor 70, sine wave oscillation having the frequency ω is performed.

Transfer function K of the two phase shift circuits 10 and 10a
When the time constant of the CR circuit in each phase shift circuit is T, 21 replaces T ₁ with T in (17),

[Equation 22] Becomes Therefore, these two phase shift circuits 10, 10
The overall transfer function K41 when a is cascaded is

(Equation 23) Becomes Therefore, these two phase shift circuits 10, 10
The overall transfer function K5 when the phase inversion circuit 80 is connected to the subsequent stage of a is

[Equation 24] Becomes The right side of the equation (24) is equal to the transfer function K ₁ shown in the equation (19) in the first embodiment with T ₁ and T ₂ replaced with T. That is, the equation (24) is equal to the overall transfer function when the two phase shift circuits 10 and 30 shown in the first embodiment are connected, and in this embodiment, two phase shift circuits 10 of the same type are used. , 10a and the phase inversion circuit 80 are connected to each other is equivalent to the structure in which the two phase shift circuits 10 and 30 of different types are connected in the first embodiment.

From another point of view, the overall transfer function in the case of connecting the subsequent phase shift circuit 10a and the phase inversion circuit 80 shown in FIG. 10 has the sign of the transfer function of one phase shift circuit 10a. It can be said that it is an inverted one. Therefore, (1
The sign "-" of the transfer function K2 of the phase shift circuit 10a shown in the expression (7) is inverted to "+", which is the entire transfer function connecting the phase shift circuit 10a and the phase inversion circuit 80. In any case, it becomes equal to the transfer function K3 of the phase shift circuit 30 shown in the equation (18) when T ₁ = T ₂ . Even if considered in this way, the configuration in which two phase shift circuits 10 and 10a of the same type and the phase inversion circuit 80 are connected in the present embodiment has two different phase shift circuits 10 and 30 in the first embodiment. It can be seen that this is equivalent to the configuration in which is connected.

Therefore, in the oscillator 2c of this embodiment, by setting the amplification factor of the phase inverting circuit 80 to an appropriate value and setting the loop gain to 1 or more, the phase shift amount becomes 0 ° when the circuit makes one cycle. Sine wave oscillation is sustained at various frequencies. Moreover, the capacitance of the condenser microphone 14a-2 connected to the second-stage phase shift circuit 10a changes according to the sound pressure, and the amount of phase shift in the phase shift circuit 10a also changes according to the sound pressure. , It is possible to directly generate an FM-modulated signal from voice and output it from the output terminal 92. The FM-modulated signal output from the output terminal 92 is emitted from the antenna 1 into the air.

As described above, the FM wireless microphone of this embodiment is similar to the FM wireless microphone of the first embodiment.
The capacitance change of the condenser microphone 14a-2 is directly used for FM modulation, and the circuit configuration can be simplified. Further, the FM wireless microphone of this embodiment is suitable for integration of the entire circuit except the condenser microphone 14a-2 because the oscillator 2c is composed of only the operational amplifier, the resistor and the capacitor and does not use the inductor. Also, it is not necessary to take measures such as magnetic shielding when using an inductor.

In the FM wireless microphone of this embodiment, the condenser microphone is connected to the second-stage phase shift circuit, but the condenser microphone may be connected to the first-stage phase shift circuit. That is, the oscillator may be configured by replacing the arrangement of the two phase shift circuits 10 and 10a shown in FIG.

(Third Embodiment) The FM of the second embodiment described above.
In the wireless microphone, two-type phase shift circuits 10, 10 are used.
Although the case where a is connected in two stages has been described, the oscillator may be configured by connecting two + type phase shift circuits in two stages.

FIG. 11 is a diagram showing the structure of the FM wireless microphone of the third embodiment, showing the detailed structure of the oscillator 2d.

The oscillator 2d shown in FIG.
The two + type phase shift circuits 30a and 30 shown in FIG. 2 and a phase inversion circuit 80 that further inverts the phase of the output signal of the subsequent phase shift circuit 30 and performs power amplification, and a phase inversion circuit 80.
And a feedback resistor 70 that feeds back the output of the above to the input side of the phase shift circuit 30a at the previous stage.

The phase inverting circuit 80 is the one shown in FIG. 10 in the second embodiment. When an AC signal is input to the inverting input terminal of the operational amplifier 82 via the resistor 84, the phase inverting circuit 80 outputs from the output terminal of the operational amplifier 82. A reverse-phase signal whose phase is inverted is output. Further, by performing power amplification by the phase inversion circuit 80, it is possible to increase the output of the FM carrier transmitted from the antenna 1 to the air.

As described in the first embodiment, +
In each of the two type phase shift circuits 30a and 30, the phase shift amount changes from 0 ° to 180 ° as the frequency ω of the input signal changes from 0 to ∞. For example, 2
Assuming that the time constants of the CR circuits in the two phase shift circuits 30a and 30 are the same, and letting that value be T, the phase in each of the two phase shift circuits 30a and 30 at the frequency of ω = 1 / T. The shift amount becomes 90 °. Therefore, the phase is shifted by 180 ° by the two phase shift circuits 30a and 30, and the phase is inverted by the phase inversion circuit 80 connected to the subsequent stage, and the phase is rotated once and the shift amount becomes 0 ° as a whole. Signal is output from the phase inversion circuit 80. Therefore, by feeding back the output of the phase inversion circuit 80 to the input side of the phase shift circuit 30a at the preceding stage via the feedback resistor 70, sine wave oscillation having the frequency ω is performed.

By the way, regarding the transfer function K31 of the two phase shift circuits 30a and 30, assuming that the time constant of the CR circuit in each phase shift circuit is T, T ₂ is replaced by T in the equation (18),

(Equation 25) Becomes This transfer function K31 is obtained by replacing the sign "-" of the transfer function K21 shown in the equation (22) with "+",
The overall transfer function K41 when the two phase shift circuits 30a and 30 are connected in series is shown in the second embodiment (23).
You can apply the formula as is. Therefore, the equation (24) shown in the second embodiment can be applied as it is to the entire transfer function K5 when the phase inverting circuit 80 is connected at the subsequent stage of these two phase shift circuits 30a and 30.

That is, in the present embodiment, 2 of the same type
The configuration in which the two phase shift circuits 30a and 30 and the phase inversion circuit 80 are connected has a configuration in which two phase shift circuits 10 and 30 of different types are connected in the first embodiment, and a negative type 2 in the second embodiment. It can be said that this is equivalent to the configuration in which the two phase shift circuits 10 and 10a and the phase inversion circuit 80 are connected.

From another point of view, the entire transfer function when the phase shift circuit 30 and the phase inversion circuit 80 in the latter stage shown in FIG. 11 are connected is the sign of the transfer function of one phase shift circuit 30. It can be said that it is an inverted one. Therefore, (18)
The sign "+" of the transfer function K3 of the phase shift circuit 30 shown in the equation is inverted to "-" to become the entire transfer function connecting the phase shift circuit 30 and the phase inversion circuit 80. Note that the transfer function K2 of the phase shift circuit 10 shown in the equation (17) when T ₁ = T ₂ is not satisfied. Even if considered in this way, two phase shift circuits 3 of the same type in this embodiment are used.
0a, 30 and the phase inversion circuit 80 are connected to each other, two phase shift circuits 10 of different types in the first embodiment,
It can be seen that this is equivalent to the configuration in which 30 is connected.

Therefore, in the oscillator 2d of the present embodiment, by setting the amplification factor of the phase inverting circuit 80 to an appropriate value and setting the loop gain to 1 or more, the phase shift amount becomes 0 ° when the circuit makes one cycle. Sine wave oscillation is sustained at various frequencies. Moreover, the capacitance of the condenser microphone 34-2 connected to the second-stage phase shift circuit 30 changes according to the sound pressure, and the amount of phase shift in the phase shift circuit 30 also changes according to the sound pressure. , It is possible to directly generate an FM-modulated signal from voice and output it from the output terminal 92. The FM-modulated signal output from the output terminal 92 is emitted from the antenna 1 into the air.

As described above, the FM wireless microphone of this embodiment directly changes the capacitance of the condenser microphone 34-2 into FM modulation, as in the FM wireless microphones of the first and second embodiments. Since it is used, the circuit configuration can be simplified. Further, the FM wireless microphone of this embodiment is suitable for integration of the entire circuit except the condenser microphone 34-2 because the oscillator 2d is composed of only an operational amplifier, a resistor and a capacitor and does not use an inductor. Also, it is not necessary to take measures such as magnetic shielding when using an inductor.

In the FM wireless microphone of this embodiment, the condenser microphone is connected to the second-stage phase shift circuit, but the condenser microphone may be connected to the first-stage phase shift circuit. That is, the oscillator may be configured by replacing the arrangement of the two phase shift circuits 30a and 30 shown in FIG.

The present invention is not limited to the above embodiments, but various modifications can be made within the scope of the gist of the present invention.

For example, in each of the above-described embodiments, the case where the condenser microphone and the capacitor are connected in series has been described. In principle, however, the condenser microphone and the capacitor connected in series function as one capacitor. Therefore, the capacitor connected in series to the condenser microphone may be omitted, the condenser microphone may be connected in parallel, or the condenser microphone and a plurality of capacitors may be combined in parallel and in series. Comparing the case where the condenser microphone is used alone and the case where the condenser microphone and the capacitor are connected in series or in parallel or in combination thereof, in the latter case, by changing the capacitance value of the connected capacitor, The degree of change in the capacitance of
That is, there is an advantage that the FM modulation degree can be adjusted.

Further, in the first embodiment, F shown in FIG.
In the M wireless microphone, the output terminal 9 is connected to the non-inverting circuit 50.
2 is connected, but the output terminal 92 is connected to the phase shift circuit 10 or the like at the front stage or the rear stage, and the FM-modulated signal output from the output terminal 92 is directly passed to the antenna 1 or after passing through the power amplification circuit. It may be sent to the antenna 1. Similarly, in the second and third embodiments, the output terminal 92 is connected to the phase inversion circuit 80, but the output terminal 92 is connected to the phase shift circuit in the preceding stage or the phase shift circuit in the subsequent stage, and this output terminal The FM-modulated signal output from 92 may be sent directly to the antenna 1, or may be sent to the antenna 1 after passing through the power amplifier circuit.

Further, in each of the embodiments described above, the FM wireless microphone having a fixed transmission frequency is realized by fixing the element constant of each element in each phase shift circuit. However, by changing each element constant, the frequency is changed. May be changed arbitrarily. For example, referring to FIG. 1 as an example, the phase shift circuit 10
Alternatively, by replacing at least one of the resistors 16 and 36 in 30 with a variable resistor and varying the resistance value,
Alternatively, the capacitor 1 in the phase shift circuit 10 or 30
By replacing at least one of 4, 34-1 with a variable capacitance element and varying the capacitance, the phase shift amount can be changed by each phase shift circuit to change the transmission frequency. More specifically, the variable resistance described above can be formed by the channel of the FET whose gate voltage can be changed, and the variable capacitance diode which applies the variable bias element between the anode and the cathode and whose reverse bias voltage can be changed, Alternatively, it can be formed by an FET whose gate capacitance can be changed by the gate voltage.

In particular, when a variable resistance is formed using the channel of the FET, one variable resistance is formed by connecting the p-channel FET and the n-channel FET in parallel,
It is also possible to apply gate voltages having the same magnitude and different polarities between the gate and the substrate of each FET.
As described above, by combining the two FETs to form the variable resistance, it is possible to improve the non-linear region of the FET, and it is possible to transmit the FET carrier with reduced distortion and less distortion.

In addition to the case where the variable resistor or the variable capacitance element is used as described above, a plurality of resistors or capacitors having different element constants are prepared and the switch is switched to select from among the plurality of elements. One or more may be selected. In this case, since the element constants can be switched discontinuously, the FM
The transmission frequency of the wireless microphone can be switched discontinuously. Therefore, it is suitable for applications in which the frequency is switched to avoid interference.

When the oscillators of the respective embodiments are integrated, electrodes are formed via an insulating oxide film such as SiO ₂ or a capacitor is formed by using the gate capacitance of FET as described above. can do.

Further, in each of the above-described embodiments, the oscillator having high stability can be constructed by constructing the phase shift circuits 10, 30 and the like using the operational amplifier, but it is used as in the present invention. In this case, since the offset voltage and the voltage gain are not required to have high performance, a differential input amplifier having a predetermined amplification degree may be used instead of the operational amplifier in each phase shift circuit.

FIG. 12 is a circuit diagram in which a part necessary for the operation of the phase shift circuit of each embodiment is extracted from the configuration of the operational amplifier, and the whole operates as a differential input amplifier having a predetermined amplification degree. The differential input amplifier shown in the figure includes a differential input stage 100 including FETs, and a differential input stage 100.
Constant current circuit 102 for applying a constant current to the constant current circuit 10
Bias circuit 104 for applying a predetermined bias voltage to 2
And an output amplifier 106 connected to the differential input stage 100. As shown in the figure, omitting the offset adjustment circuit and the like included in the actual operational amplifier,
The configuration of the differential input amplifier can be simplified. Since the upper limit of the operating frequency can be increased by simplifying the circuit in this way, the upper limit of the operating frequency of the tuning amplifier 1 and the like configured by using this differential input amplifier is correspondingly increased. You can

[0125]

As described above, according to the first to fifth aspects of the invention, the FM modulation can be directly performed by utilizing the change in the capacitance of the condenser microphone, and the change in the capacitance can be changed once. Since an additional circuit such as conversion to change is unnecessary, FM
The circuit configuration of the entire wireless microphone can be simplified. Further, since sinusoidal wave oscillation is performed without using an inductor or the like, integration can be easily performed on the semiconductor substrate.

According to the sixth aspect of the invention, the differential input amplifier included in the phase shift circuit is specifically configured by an operational amplifier, and the stability of the entire circuit can be increased.

Further, according to the invention of claim 7, instead of using the condenser microphone itself as a capacitor, it is combined with a capacitor having a fixed capacitance, and the combination is made according to the combination method and the capacitance of the combined capacitor. It is possible to arbitrarily adjust the ratio of the change in the capacitance of the condenser microphone to the change in the overall capacitance after that, and it is possible to easily adjust the FM modulation degree.

According to the eighth to tenth aspects of the invention, the variable resistance is formed by the FET by changing the resistance value of the third resistor included in the phase shift circuit in the oscillator. By changing the channel resistance by changing the channel resistance, the phase shift amount in the phase shift circuit changes.
The frequency of the M carrier can be changed arbitrarily.
Especially when a variable resistance is formed by FET, p
By using the channel FET and the n-channel FET in parallel, it is possible to improve the non-linear region of the FET, and it is possible to transmit an FM carrier with reduced harmonic components and less distortion.

According to the eleventh aspect of the present invention, instead of using the variable resistor, the capacitor is formed by the variable capacitance element, so that the amount of phase shift in the phase shift circuit is changed, whereby the frequency of the FM carrier to be transmitted is changed. Can be changed arbitrarily.

According to the twelfth or thirteenth aspect of the present invention, instead of using an element whose element constant itself is variable, such as a variable resistance or a variable capacitance element, a plurality of elements having different element constants are used as resistors and capacitors. Prepare and use one of the elements by switching the switch.
Therefore, the frequency of the FM-modulated signal can be changed discontinuously. For example, it is suitable for preparing a plurality of frequencies to avoid interference.

According to the fourteenth aspect of the present invention, the entire oscillator is integrally formed on the semiconductor substrate, and it is possible to reduce the size of the circuit and reduce the manufacturing cost by integration.

[0132]

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an FM wireless microphone according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an extracted configuration of a phase shift circuit at a preceding stage shown in FIG.

FIG. 3 is a vector diagram showing the relationship between the input / output voltage of the preceding phase shift circuit and the voltage appearing in a capacitor or the like.

FIG. 4 is a diagram showing an extracted configuration of a phase shift circuit at a subsequent stage shown in FIG.

FIG. 5 is a vector diagram showing a relationship between an input / output voltage of a subsequent phase shift circuit and a voltage appearing in a capacitor or the like.

FIG. 6 is a system diagram in which the entire two phase shift circuits are replaced with a circuit having a transfer function K1.

FIG. 7 is a system diagram obtained by converting the system shown in FIG. 6 according to Miller's theorem.

FIG. 8 is a diagram showing a modification of the FM wireless microphone of the first embodiment.

FIG. 9 is a diagram showing a modified example of the FM wireless microphone of the first embodiment.

FIG. 10 is a diagram showing a configuration of an FM wireless microphone according to a second embodiment.

FIG. 11 is a diagram showing a configuration of an FM wireless microphone of a third embodiment.

FIG. 12 is a circuit diagram in which a part necessary for the operation of the phase shift circuit of the present invention is extracted from the configuration of the operational amplifier.

[Explanation of symbols]

1 Antenna 2 Oscillator 10,30 Phase shift circuit 12,32,52 Operational amplifier 14,34-1 Capacitor 16,18,20,36,38,40,54,56 Resistor 34-2 Capacitor microphone 50 Non-inverting circuit 70 Feedback resistor 92 output terminals

Claims (14)

[Claims] 1. An FM wireless microphone including a condenser microphone that collects sound, an oscillator to which the condenser microphone is connected, and an antenna that outputs a signal output from the oscillator to the air, wherein the oscillator is an inverted A differential input amplifier having one end of a first resistor connected to an input terminal, a second resistor connected between an inverting input terminal and an output terminal of the differential input amplifier, and the first resistor. And a series circuit including a third resistor and a capacitor connected to the other end of the differential input amplifier, and a connection part of the third resistor and the capacitor is connected to a non-inverting input terminal of the differential input amplifier. A circuit, wherein the output of the phase shift circuit at the subsequent stage is fed back to the input side of the phase shift circuit at the previous stage, and the condenser microphone is included in either one of the two phase shift circuits. An FM wireless microphone characterized by outputting an FM-modulated signal from either of the two phase shift circuits by using as a capacitor. 2. An FM wireless microphone including a condenser microphone that collects sound, an oscillator to which the condenser microphone is connected, and an antenna that outputs a signal output from the oscillator to the air, wherein the oscillator is an inverted A differential input amplifier having one end of a first resistor connected to an input terminal, a second resistor connected between an inverting input terminal and an output terminal of the differential input amplifier, and the first resistor. And a series circuit including a third resistor and a capacitor connected to the other end of the differential input amplifier, and a connection part of the third resistor and the capacitor is connected to a non-inverting input terminal of the differential input amplifier. A non-inverting circuit for amplifying and outputting power without changing the phase of the AC signal output from the phase shift circuit connected to the latter stage, and connecting the output of the non-inverting circuit to the preceding stage. The FM-modulated signal is output from the non-inverting circuit by feeding back the input signal to the input side of the phase-shifting circuit and using the condenser microphone as the capacitor included in one of the two phase-shifting circuits. FM wireless microphone characterized by. 3. The FM wireless microphone according to claim 1, wherein the connection between the third resistor and the capacitor forming the series circuit is reversed in the two phase shift circuits. . 4. An FM wireless microphone including a condenser microphone that collects voice, an oscillator to which the condenser microphone is connected, and an antenna that outputs a signal output from the oscillator to the air. A differential input amplifier having one end of a first resistor connected to an input terminal, a second resistor connected between an inverting input terminal and an output terminal of the differential input amplifier, and the first resistor. And a series circuit including a third resistor and a capacitor connected to the other end of the differential input amplifier, and a connection part of the third resistor and the capacitor is connected to a non-inverting input terminal of the differential input amplifier. And a phase inverting circuit that inverts the phase of the AC signal output from the phase shift circuit connected to the subsequent stage and that amplifies and outputs the power, and outputs the phase inverting circuit. Is fed back to the input side of the phase shift circuit connected to the preceding stage, and the capacitor microphone is used as the capacitor included in either one of the two phase shift circuits, whereby FM modulation is performed from the phase inversion circuit. An FM wireless microphone that outputs a signal. 5. The FM wireless microphone according to claim 4, wherein the third resistor and the capacitor forming the series circuit are connected in the same manner in the two phase shift circuits. 6. The FM wireless microphone according to claim 1, wherein the differential input amplifier is an operational amplifier. 7. The FM wireless microphone according to claim 1, wherein a capacitor having a fixed capacitance is connected in series or in parallel with the capacitor microphone. 8. The FM wireless microphone according to claim 1, wherein the third resistor included in at least one of the two phase shift circuits is a variable resistor. 9. The FM wireless microphone according to claim 8, wherein the variable resistance is formed by a channel of a field effect transistor, and a channel voltage is changed by changing a gate voltage. 10. The variable resistance according to claim 8, wherein the variable resistance is formed by connecting a p-channel type field effect transistor and an n-channel type field effect transistor in parallel, and a gate voltage of each field effect transistor having a different polarity is formed. An FM wireless microphone characterized by changing the size and changing the channel resistance. 11. The FM wireless microphone according to claim 1, wherein the capacitor included in at least one of the two phase shift circuits is a variable capacitance element. 12. The method according to claim 1, wherein a plurality of resistors having a fixed resistance value are provided as the third resistors included in at least one of the two phase shift circuits, and are switched by a switch. An FM wireless microphone that is selectively connected. 13. The capacitor according to claim 1, wherein the capacitors included in at least one of the two phase shift circuits have a plurality of capacitors having a fixed capacitance, and are selectively switched by switching. FM wireless microphone characterized by connecting to. 14. The FM wireless microphone according to claim 1, wherein each component of the oscillator is integrally formed on a semiconductor substrate.