JP3219218B2 - Modulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Table of Contents] The present invention will be described in the following order. BACKGROUND OF THE INVENTION Problems to be Solved by the Invention Means for Solving the Problems (FIG. 1) Function (FIG. 1) Embodiment (FIGS. 1 and 2) Effects of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulation circuit, for example, an RF (radio frequency) for FM-modulating and outputting a voice signal.
y) It is suitable for use in a modulator circuit of a modulator.

[0003]

2. Description of the Related Art Conventionally, there is a modulation circuit of this type which can switch the frequency of a subcarrier by selecting one of a plurality of set frequencies. Normally, in these modulation circuits, the frequency of the subcarrier is switched by a switch switching operation. If this can be performed in one RF modulator integrated circuit, the circuit can be downsized compared to the conventional one. It is considered something.

[0004]

However, in such an audio FM modulation circuit of an RF modulator integrated circuit, the frequency deviation of the modulation increases in proportion to the frequency of the audio subcarrier, and as a result, the demodulated audio There is a problem that the magnitude (sensitivity) changes according to the frequency of the audio subcarrier. Conventionally, in a modulation circuit, an output signal is output to a subsequent circuit after passing through a low-pass filter circuit in order to reduce a harmonic component of an audio subcarrier, but in this case, the frequency characteristic of the low-pass filter circuit is reduced. Therefore, when the frequency of the carrier wave increases, the signal level of the output signal output from the low-pass filter circuit decreases.

The present invention has been made in view of the above points, and it is an object of the present invention to propose a modulation circuit that can always keep the modulation sensitivity constant regardless of the frequency of the subcarrier.

[0006]

In order to solve this problem, the present invention comprises a plurality of oscillating circuits, and by switching predetermined switching means 4 and 9, the frequency of the audio subcarrier is changed to each oscillation frequency. In the modulation circuit 1 that can select one of a plurality of types of frequencies oscillated in the circuit and set the selected frequency, the magnitude of the resistance value of the damping resistor R1 in the first oscillation circuit among the plurality of oscillation circuits , The damping resistor R in the second oscillation circuit
The ratio of the magnitude of the resistance value of 10, the oscillation frequency omega ₁ of the first oscillation circuit size and the ratio becomes equal as in the first and second and the magnitude of the oscillation frequency omega ₂ of the second oscillator circuit The resistance values of the damping resistors R1 and R10 of the oscillation circuit were set.

Further, in the present invention, the modulation circuit 1 is provided with a low-pass filter circuit 30 having input / output characteristics opposite to the frequency characteristic of the oscillation level of each oscillation circuit, and outputs the output signal of each oscillation circuit to the low-pass filter circuit 30. Output via.

Further, according to the present invention, each oscillation circuit includes:
An oscillation source 1 or 10 in which a coil L1 or L10 and a capacitor C1 or C10 are connected in parallel;
1 or Q10 and the constant current source 5 connected to the emitter of the transistor Q1 or Q10. The output signal of the oscillation source 1 or 10 is received at the base of the transistor Q1 or Q10, and the output of the transistor Q1 or Q10 and the constant current source 5 a buffer for outputting from the connection point via a capacitor C2 or C11, is connected between the base of the transistor Q1 or Q10 of the buffer and the constant current line V _CC, a damping resistor R1 or applying a base voltage to the transistor Q1 or Q10 of buffer R10 and a pair of transistors Q
3 and Q4, a buffer output signal is supplied to the base of the first transistor Q2, the base of the second transistor Q4 is grounded, and the second transistor Q4 And a differential amplifier connected to the base of a buffer transistor Q1 or Q10.

[0009]

The ratio between the magnitude of the resistance value of the damping resistor R1 in the first oscillation circuit and the magnitude of the resistance value of the damping resistor R10 in the second oscillation circuit of the plurality of oscillation circuits is equal to the ratio of the resistance value of the first oscillation circuit. By setting the resistance values of the damping resistors R1 and R10 of the first and second oscillation circuits to be equal to the ratio between the magnitude of the oscillation frequency ω1 and the magnitude of the oscillation frequency ω2 in the second oscillation circuit, the first In addition, the frequency deviations ω _d1 and ω _{d2 of the} subcarriers generated in the second oscillation circuit become equal, and thus a modulation circuit capable of always keeping the modulation sensitivity constant irrespective of the frequency of the subcarrier can be realized.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

In FIG. 1, reference numeral 1 denotes an audio frequency FM modulation circuit composed of one integrated circuit as a whole, and is constituted by first and second oscillation circuits. That is, in the first oscillating circuit, the first oscillating unit 2 in which the coil L1 and the capacitor C1 are connected in parallel is used as an oscillating source.
In the oscillation section 2, one connection point P1 of the coil L1 and the capacitor C1 is grounded, and the other connection point P2 is connected to the base of the transistor Q1 of the audio subcarrier modulation section 3 and the collector of the transistor Q2, respectively. It is connected.

In the transistor Q1, a base is connected to a constant voltage line V _CC via a resistor R1 (hereinafter referred to as a damping resistor R1), a collector is directly connected to the constant voltage line V _CC , and an emitter is connected. Are connected to the first switching end 4A of the switch section 4 and the emitters are respectively connected to the bases of the transistors Q3 via the capacitor C2, whereby the switch of the switch section 4 is connected to the first switching end 4A. When the emitter is grounded via the constant current source 5, a buffer is formed together with the constant current source 5 to output an output signal of a predetermined frequency supplied from the first oscillating unit 2 (hereinafter referred to as a first signal). (Referred to as an oscillation signal) to the base of the transistor Q3.

The transistor Q3 and the transistor Q4 form a differential amplifier 6 having a differential amplifier circuit configuration. The collector is grounded, the emitter is grounded via a constant current source 7, and the emitter is grounded. It is connected to the emitter of the transistor Q4 via the resistor R2.
In the transistor Q4, the emitter is grounded via the constant current source 8, the base is grounded, and the collector is connected to the emitter of the transistor Q2.

Further, in the transistor Q2, the collector is connected to a connection point P3 between the damping resistor R1 and the base of the transistor Q1, and the base is connected to the first switching terminal 9A of the switch section 9, thereby connecting the switch. When the switch of the section 9 is put into the first switching terminal 9A, the base is grounded and turned on. As a result, the base of the transistor Q3 based on the first oscillation signal amplified by the differential amplifier 6 is turned on. The change in the voltage is applied to the base of the transistor Q1 in the same phase.

In this case, in the switch section 9, when the switch of the switch section 4 is connected to the first switching end 4A, the switch is connected to the first switching end 9A in conjunction therewith. As a result, the respective switches of the switch parts 4 and 9 are connected to the first switching ends 4A and 9 respectively.
A, when connected to the first oscillator 2, the transistor Q1 and the constant current source 5, the differential amplifier 6, the transistor Q1
2 and a first oscillating circuit including a damping resistor R1 are formed, and the first oscillating source 2 in the first oscillating circuit is formed.
The following equation when the self-inductance of the coil L1 and L _x, and the capacitance of the capacitor C2 and the C _x

(Equation 1) It is adapted to generate an oscillation frequency omega ₁ of the audio subcarrier (hereinafter referred to as first audio subcarrier) THAT represented.

Similarly, in the second oscillating circuit, the second oscillating unit 10 in which a coil L10 and a capacitor C10 are connected in parallel is used as an oscillating source, and the second oscillating unit 10
In the example, one connection midpoint P10 of the coil L10 and the capacitor C10 is grounded, and the other connection midpoint P11 is connected to the base of the transistor Q10 and the collector of the transistor Q11, respectively.

The transistor Q10 has a base connected to a resistor R1.
0 (hereinafter this is referred to as damping resistors R10) collector is connected to the constant voltage line V _CC via the well connected to the constant voltage line V _CC, and the second switching terminal 4B and capacitors emitter is switch section 4 It is connected to the base of the transistor Q3 via C11, so that the switch of the switch section 4 is inserted into the second switching terminal 4B and the emitter is grounded via the constant current source 5 together with the constant current source 5. A buffer is formed so that an output signal of a predetermined frequency supplied from the second oscillating unit 10 (hereinafter referred to as a second oscillating signal) is output to the base of the transistor Q3.

In the transistor Q11, the collector is connected to the midpoint P12 between the damping resistor R11 and the base of the transistor Q10, the emitter is connected to the collector of the transistor Q4, and the base is the second terminal of the switch unit 9. Is connected to the switching end 9B of the second switching end 9B.
B, the base is grounded and turned on. As a result, the second amplifier amplified by the differential amplifier 6
The change in the base voltage of the transistor Q3 based on the oscillation signal is supplied to the base of the transistor Q10.

In this case, in the switch section 9, when the switch of the switch section 4 is connected to the second switching end 4B, the switch is connected to the second switching end 9B in conjunction with this connection. As a result, the second oscillating unit 10, the transistor Q10 and the constant current source 5, the differential amplifying unit 6, the transistor Q11, and the second
Oscillation circuit is formed of a self-inductance of the coil L10 of the second second oscillation source 10 in the oscillation circuit of the L _y, and the following equation when the capacitance of the capacitor C10 and the C _y

(Equation 2) It is adapted to generate an oscillation frequency omega ₂ of the audio subcarrier (hereinafter referred to as the second audio subcarrier) THAT represented.

Further, in the audio subcarrier modulation section 3, the collector of the transistor Q4 and the transistor Q3
Is 90 ° and the phase shift capacitor C20
And a multiplier 20, and an audio signal source 21 is connected to the multiplier 20, whereby the first or second audio sub-signal is output based on the audio signal output from the audio signal source 21. The carrier is modulated.

A low-pass filter circuit 30 comprising a resistor R30 and a capacitor C30 is connected to a signal output terminal of the audio sub-carrier modulation section 3 which is a connection point P20 between the base of the transistor Q3 and the capacitors C2 and C11. Thus, the first and second audio subcarriers modulated by the audio subcarrier modulation unit 3 are sent to a subsequent circuit after their high frequency components are removed by the low-pass filter circuit 30. I have.

Here, in the first and second oscillation circuits, the signal level v _S of the audio signal output from the audio signal source 21 is expressed by the following equation.

(Equation 3) (Where t is time), the frequency deviation in each oscillation circuit is changed from ω _d1 and ω _d2 from the connection middle point P20, respectively.
And

(Equation 4)

(Equation 5) The first and second audio sub-carriers of the signal levels v ₁ and v ₂ represented by are output.

In this case, the frequency deviations ω _d1 and ω _d2 in the first and second oscillation circuits are represented by the proportional constant K ₁ and the resistance values of the resistors R ₁ and R 10 as R _d1 and R _d2 , respectively. Next formula

(Equation 6)

(Equation 7) Can be represented by Therefore, in the audio frequency modulation circuit 1, the damping resistances R1 and R10 are calculated by the following equations from the equations (6) and (7).

(Equation 8) By setting the resistance value to satisfy
Frequency deviations ω _d1 and ω in first and second oscillation circuits
_d2 is made equal (that is, ω _d1 = ω _d2 ).

Furthermore this case, the first and second audio subcarrier output level v ₁ and v ₂ of the output from the connection point P20, when the proportional constant is K _2, the following equations

(Equation 9)

(Equation 10) And therefore damping resistors R1 and R1
If 0 satisfies the expression (8), the following expression is obtained from the expressions (8), (9) and (10).

[Equation 11] Is derived, it can be seen that the frequency characteristics of the oscillation output levels of the first and second oscillation circuits have the same predetermined value (for example, 6 [dB / oct]).

At this time, the input / output characteristics of the low-pass filter circuit 30 are set so as to be opposite to the frequency characteristics of the oscillation output levels of the first and second oscillation circuits (for example, -6 [dB / oct]). FIG. 2
As shown in FIG. 7, the level characteristics of the first and second audio subcarriers and the input / output characteristics of the low-pass filter circuit 30 cancel each other out, and the signal of the audio frequency modulation circuit 1 at the output end of the low-pass filter circuit 30 is cancelled. From the output terminal out, an output signal having a constant signal level v ₁ and v ₂ is output regardless of the frequency of the audio subcarrier.

In the above configuration, in the audio frequency modulation circuit 1, when the switches of the switch sections 4 and 9 are connected to the first switching ends 4A and 9A, respectively, the first
When the switches of the switch units 4 and 9 are connected to the second switching terminals 4B and 9B, a second oscillator circuit is formed. In this case, the first and second oscillation circuits oscillate the first and second audio subcarriers having the oscillation frequencies given by the equations (1) and (2), respectively, Frequency deviations ω _d1 and ω _d2 given by the equations (6) and (7) occur in the voice subcarrier.

However, in the audio frequency modulation circuit 1, the resistance values of the damping resistors R1 and R10 are (8)
Since the setting is made so as to satisfy the expression, the frequency deviations ω _d1 and ω _d2 given by the expressions (6) and (7) match, and as a result, the signal output end ou of the audio frequency modulation circuit 1 concerned.
From t, output signals having constant frequency deviations ω _d1 and ω _d2 are always output irrespective of the oscillation frequencies of the first and second oscillation circuits.

Further, the oscillation output levels of the first and second oscillation circuits at this time are given by equations (9) and (10), respectively.
Since _{the d1} and omega _d2 is (8) the resistance of the damping resistors R1 and R10 so as to satisfy the equation is set, the frequency characteristic of the oscillation output level of the first and second oscillator circuit is constant, Since the input / output characteristics of the low-pass filter circuit 30 are set to be opposite to the frequency characteristics of the oscillation levels of the first and second oscillation circuits, the signal output terminal out.
Outputs an output signal having a constant signal level regardless of the frequency of the audio subcarrier.

According to the above configuration, in the audio frequency modulation circuit 1 having the audio subcarrier switching function, which is capable of selecting one of two types of audio subcarrier frequency, the resistances of the damping resistors R1 and R10 are set. By setting the value so as to satisfy the expression (8), the frequency deviation ω _{d1 of the} audio subcarrier output from the first and second oscillation circuits is obtained.
And ω _d2 can be equalized, thus realizing a modulation circuit that can always keep the voice FM modulation sensitivity constant regardless of the frequency of the voice subcarrier.

Further, the input / output characteristics of the low-pass filter circuit 30 are set to be opposite to the input / output characteristics of the audio subcarrier modulation unit 3, so that the frequencies of the oscillation levels of the first and second oscillation circuits are changed. The characteristics are offset by the input / output characteristics of the low-pass filter circuit 30, so that the signal level of the output signal of the audio frequency modulation circuit 1 can be kept constant irrespective of the frequency of the audio subcarrier.

In the above-described embodiment, a case has been described in which the present invention is applied to the audio frequency modulation circuit 1 including the first and second oscillation circuits. The present invention can also be applied to a modulation circuit including one or more oscillation circuits.

[0032]

As described above, according to the present invention, in an RF modulator having a subcarrier switching function, the first of a plurality of oscillation circuits constituting the RF modulator is provided.
The ratio between the magnitude of the resistance value of the damping resistor in the second oscillation circuit and the magnitude of the resistance value of the damping resistor in the second oscillation circuit is the difference between the oscillation frequency of the first oscillation circuit and the oscillation frequency of the second oscillation circuit. By setting the resistance values of the damping resistors of the first and second oscillation circuits to be equal to the ratio, the frequency deviations of the subcarriers generated in the first and second oscillation circuits become equal, and thus the A modulation circuit capable of keeping the modulation sensitivity constant irrespective of the carrier frequency can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an audio frequency modulation circuit according to one embodiment of the present invention.

FIG. 2 is a graph for explaining a signal level of an output signal of the audio frequency modulation circuit shown in FIG. 1;

[Explanation of symbols]

1 ... audio frequency modulation circuit, 2, 10 ... oscillation source, 4,
9 switch part, 5, 7, 8 ... constant current source, 6 ... differential amplifying part, 21 ... audio signal source, 30 ... low-pass filter circuit, Q1-Q5, Q10, Q12 ... transistor, L1, L2 ... coil, C1, C2, C10, C1
1, C20, C30 ... capacitor, R1, R2, R1
0, R30 ... resistance.

Claims (3)

(57) [Claims] The present invention comprises a plurality of oscillation circuits, and selects one of a plurality of types of frequencies oscillated in each of said oscillation circuits by selecting a frequency of an audio subcarrier by switching predetermined switching means. In the modulation circuit that can be set to the selected frequency, a ratio of a magnitude of a resistance value of a damping resistor in a first oscillation circuit of the plurality of oscillation circuits to a magnitude of a resistance value of a damping resistor in a second oscillation circuit. But the first
A modulation circuit, wherein the resistance value of the damping resistance of the first and second oscillation circuits is set to be equal to the ratio of the oscillation frequency of the oscillation circuit to the oscillation frequency of the second oscillation circuit. 2. The modulation circuit according to claim 1, further comprising a low-pass filter circuit having an input / output characteristic opposite to a frequency characteristic of an oscillation level of each of said oscillation circuits, and outputting an output signal of each of said oscillation circuits via said low-pass filter circuit. 2. The modulation circuit according to claim 1, wherein the modulation circuit outputs a signal. 3. Each of the oscillation circuits includes an oscillation source having a coil and a capacitor connected in parallel, a transistor and a constant current source connected to an emitter of the transistor, and outputs an output signal of the oscillation source to the transistor. A buffer that receives an output signal from a connection point of the transistor and the constant current source via a capacitor, and is connected between the base of the transistor and a constant current line of the buffer, and is connected to the transistor of the buffer. It consists of the above-mentioned damping resistor for applying the base voltage and a differential amplifier circuit configuration using a pair of transistors.
The output signal of the buffer is supplied to the base of the first transistor, the base of the second transistor is grounded, and the collector of the second transistor is connected to the base of the transistor of the buffer. The modulation circuit according to claim 1, further comprising: a differential amplifier.