JP4194135B2 - Transmitter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a low-cost transmitter that can transmit a radio wave of the amplitude modulation.
[0002]
[Prior art]
Conventionally, as this kind of amplitude modulation circuit, one using a double balanced mixer (DBM) or an analog multiplier is known (for example, “Transistor Technology”, September 1993, pp. 282-285). , And “New Low Frequency / High Frequency Design Manual”, Masahiro Suzuki, CQ Publisher, published April 30, 1988, pp. 203-206). Also, transistor amplifiers that superimpose a modulation signal on a carrier wave or that use a ring modulator are known ("Transistor Technology SPECIAL" No. 47, pp. 55-57).
[0003]
[Problems to be solved by the invention]
However, the conventional amplitude modulation circuit has problems such as the necessity of using dedicated components for high frequency and a large number of circuit parameters to be adjusted at the design stage. For example, the amplitude modulation circuit using the DBM or the analog multiplier uses a dedicated IC designed as a DBM or an analog multiplier. Further, a DC component is applied to the modulation signal to be set so as to lose the balance or to multiply the carrier wave. It was also necessary to make adjustments such as adding. In addition, in the amplitude modulation circuit using the transistor amplifier, a transformer for superimposing a modulation signal on a carrier wave is required, or setting adjustment of a bias or the like is required to use the amplifier in a linear region. In the ring modulator, it is necessary to use a diode element that can be used at a high frequency, or to use a transformer in the input / output circuit. Furthermore, a circuit for adding a carrier wave to the output signal modulated by the ring modulator is required.
[0004]
The present invention has been made in view of the above problems, and the object thereof is to be able to be configured using a general-purpose digital IC that is inexpensive and easily available, and has fewer adjustment points than a conventional circuit. parts to provide a less cost reduction can transmit machine.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the invention of claim 1 includes a pulse signal generation circuit that outputs a repetitive pulse signal repeated at a reference frequency, and a repetitive pulse signal that is repeated at the reference frequency output from the pulse oscillation circuit. A gate circuit in which the amplitude of an output signal that is input based on the input signal changes according to the power supply voltage, and a power supply voltage modulation circuit that changes the power supply voltage supplied to the gate circuit according to the modulation signal A modulation signal generating circuit that outputs a modulation signal input to the amplitude modulation circuit, and a resonance that resonates at one of a reference frequency of the output signal of the amplitude modulation circuit or an integer multiple of the reference frequency Circuit and a power supply circuit for outputting the power supply voltage, and the duty ratio of the repetitive pulse signal output from the pulse signal generation circuit is 50% Shifting al, the resonant frequency of the resonant circuit, the amplitude modulation circuit, characterized in that set in one of the even multiple of the reference frequency.
[0006]
In the amplitude modulation circuit of the transmitter according to claim 1, an input signal composed of a repetitive pulse signal repeated at the reference frequency is applied to the gate circuit in which the amplitude of the output signal output based on the input signal changes according to the power supply voltage. Entered. Then, the power supply voltage changed according to the modulation signal by the power supply voltage modulation circuit is supplied to the gate circuit, so that an output signal whose amplitude changes according to the modulation signal is output from the gate circuit. Is output as A gate circuit capable of outputting such an amplitude modulation signal can be configured using a general-purpose digital IC that is inexpensive and easily available.
Further, in the transmitter according to claim 1, the repetitive pulse signal repeated at the reference frequency output from the pulse signal generation circuit is input to the gate circuit of the amplitude modulation circuit and the modulation signal output from the modulation signal generation circuit. Is input to the power supply voltage modulation circuit of the amplitude modulation circuit. In this power supply voltage modulation circuit, the power supply voltage output from the power supply circuit is changed according to the modulation signal and supplied to the gate circuit. From the gate circuit supplied with the power supply voltage, an output signal obtained by amplitude-modulating the repetitive pulse signal with the modulation signal is output as an amplitude modulation signal. The resonance circuit resonates at one of the reference frequency of the output signal output from the amplitude modulation circuit or an integral multiple of the reference frequency, so that the carrier frequency is the resonance frequency of the resonance circuit and the amplitude is Q (resonance circuit). A sinusoidal amplitude-modulated signal that is twice the sharpness of the resonance can be obtained.
In particular, in the transmitter of claim 1, a repetitive pulse signal with a duty ratio deviating from 50% is output from the pulse signal generation circuit and input to the amplitude modulation circuit, and the amplitude modulation signal output from the amplitude modulation circuit The ratio of the harmonic signal component that is an even multiple of the reference frequency included is increased. The resonance circuit resonates at one of the multiples of the reference frequency of the output signal output from the amplitude modulation circuit, so that the carrier frequency is the resonance frequency of the resonance circuit and the amplitude is Q (resonance of the resonance circuit). A sinusoidal amplitude-modulated signal that is twice as sharp as the above can be obtained.
[0007]
According to a second aspect of the present invention, in the transmitter according to the first aspect, the impedance of the modulation signal is low with respect to the reference frequency between the output terminal of the power supply voltage modulation circuit of the amplitude modulation circuit and the ground. Is characterized in that an impedance element having a high impedance is connected.
[0008]
In the amplitude modulation circuit according to claim 2, the reference leaked from the power supply voltage input terminal of the gate circuit by the impedance element having a low impedance with respect to the reference frequency provided between the output terminal of the power supply voltage modulation circuit and the ground. Bypass the frequency signal to the ground side so that it is not input to the power supply voltage modulation circuit side. Further, since this impedance element has a high impedance with respect to the frequency of the modulation signal, the frequency band of the modulation signal input to the gate circuit is not attenuated.
[0015]
According to a third aspect of the present invention, in the transmitter of the first or second aspect , the gate circuit of the amplitude modulation circuit is configured using a single transistor element.
[0016]
In the transmitter according to the third aspect, a gate circuit including a high-power high-frequency switching circuit can be configured by using a single transistor element.
[0017]
According to a fourth aspect of the present invention, in the transmitter according to any one of the first to third aspects, an amplifier circuit for amplifying an output signal output from the resonance circuit is provided.
[0018]
In the transmitter according to the fourth aspect , an amplitude-modulated signal having a desired output level is obtained by amplifying the output signal output from the resonance circuit by the amplifier.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to an amplitude modulation circuit in a transmitter for transmitting a weak radio wave in a medium wave band (522 kHz to 1629 kHz) will be described.
[0020]
FIG. 1 is a circuit diagram of an amplitude modulation circuit according to this embodiment. This amplitude modulation circuit includes a gate circuit 1 and a power supply voltage modulation circuit 2. The gate circuit 1 is configured such that a repetitive pulse signal Vosc repeated at a reference frequency Fo is input as the input signal Vin, and the amplitude of the output signal output based on the input signal Vin changes according to the power supply voltage Vbm. ing. As this gate circuit, since it is necessary to supply a predetermined drive current to the next-stage circuit, it is preferable to use, for example, a circuit in which a plurality of logic circuit elements are connected in parallel. In the present embodiment, three NOT circuits (inverters) NOT1, NOT2, and NOT3 are connected in parallel. As this NOT circuit, a general-purpose digital IC (for example, CMOS type 74HC04) which is inexpensive and easily available can be used. The amplitude of the input signal Vin is set in accordance with a modulation power supply voltage Vbm, which will be described later, so as to be within the maximum rated range of each NOT circuit.
[0021]
The power supply voltage modulation circuit 2 changes the power supply voltage Vb supplied to each NOT circuit NOT1, NOT2, NOT3 used as the gate circuit in accordance with a modulation signal Vm such as an audio signal, and outputs it as a modulation power supply voltage Vbm. To do. In this embodiment, an emitter follower circuit using an NPN-type bipolar transistor Tr1 is used. However, the present invention is not limited to this circuit. A power supply voltage Vb (= 6 V) is applied to the collector of the transistor Tr1 from a power supply circuit (not shown). The modulation signal Vm is input to the base of the transistor Tr1 through the coupling capacitor C1, and the bias is set by the resistors R1 and R2. Further, a signal having a reference frequency Fo (= 522 KHz to 1629 kHz) of a repetitive pulse signal input to the gate circuit 1 is provided between the emitter side of the transistor Tr1 which is the output terminal of the power supply voltage modulation circuit 2 and the ground. On the other hand, a capacitor C2 having a capacitance of 0.1 μF is connected as an impedance element having a low impedance and a high impedance with respect to a signal of the modulation signal frequency Fm (for example, a voice frequency of 300 Hz to 3.0 kHz) or less. Yes. Here, the impedance of the capacitor C2 is 1.0Ω or less with respect to the carrier frequency of 1600 kHz, and about 1.6 kΩ with respect to the audio frequency of 1.0 kHz.
[0022]
The modulation operation in the amplitude modulation circuit having the above configuration will be described in the case where the modulation signal is a sine wave. A repetitive pulse signal Vosc repeated at a reference frequency Fosc (= 1 / Tosc) as shown in FIG. 2A is input as an input signal Vin to the gate circuit 1 of FIG. When a modulation signal Vm composed of a sine wave as shown in FIG. 2B, for example, is input to the power supply voltage modulation circuit 2, the power supply voltage modulated with the modulation signal Vm as shown in FIG. Vbm (2.2 to 5 V) is output and input to the power supply terminal of the digital IC package having the NOT circuits NOT1, NOT2, and NOT3. The gate circuit 1 outputs an amplitude modulation signal Vout (maximum amplitude value: 5 V, minimum amplitude value: 2.2 V) in which the repetitive pulse signal Vosc is changed according to the power supply voltage Vbm.
[0023]
FIG. 3 is a circuit diagram illustrating a configuration example of a transmitter configured using an amplitude modulation circuit including the gate circuit 1 and the power supply voltage modulation circuit 2. In addition to the amplitude modulation circuit, the transmitter outputs a pulse signal generation circuit 10 that outputs a repetitive pulse signal Vosc repeated at a reference frequency Fo, and a modulation signal Vm that is input to the power supply voltage modulation circuit 2 of the amplitude modulation circuit. A modulation signal generation circuit 20 that performs resonance, a resonance circuit 30 that resonates at the reference frequency Fo of the output signal Vout output from the gate circuit 1 of the amplitude modulation circuit, and a power supply circuit 40 that outputs a power supply voltage Vb (= 6 V). I have.
[0024]
The pulse signal generation circuit 10 uses a NOT circuit NOT4, which is a gate circuit, similarly to the amplitude modulation circuit, and has a resonance frequency Fo (for example, 1600 kHz) of the crystal resonator Xtal selected from the medium wave band (522 kHz to 1629 kHz). It is configured to oscillate stably and output a repetitive pulse signal Vosc. The NOT circuit NOT4 of the pulse signal generation circuit 10 is a digital IC different from the digital IC used in the amplitude modulation circuit. The power supply voltage Vb (= 6V) is supplied from the power supply circuit 40 to the digital IC. A repetitive pulse signal Vosc (see FIG. 2A), which is directly supplied and has a stable amplitude, can be output. Further, a voltage dividing circuit composed of resistors R4 and R5 is formed at the output portion of the pulse signal generation circuit 10, and the amplitude of the repetitive pulse signal Vosc output to the amplitude modulation circuit is set to NOT circuits NOT1, NOT2, NOT3. The input voltage is within the maximum rated range. For example, when a CMOS type digital IC is used as the NOT circuit NOT1, NOT2, NOT3 of the amplitude modulation circuit, the maximum rating of the input voltage is Vss−0.5V to Vdd + 0.5V. The values of the resistors R4 and R5 of the voltage dividing circuit are set so as not to occur. The resistor R4 is connected in parallel with a speed-up capacitor for preventing waveform distortion due to parasitic capacitance. The repetitive pulse signal Vosc divided by the voltage dividing circuit is input to the amplitude modulation circuit via a DC cut capacitor C5. The repetitive pulse signal Vosc is superimposed with a midpoint potential obtained by dividing the power supply voltage Vbm by ½ with resistors R7 and R8 (R7 = R8).
[0025]
For example, the modulation signal generation circuit 20 may be configured to amplify an audio signal converted into an electric signal by a microphone to a predetermined level and output it, or to output an audio signal stored in advance in a memory. You may comprise as follows.
[0026]
An output signal (amplitude modulation signal) Vout output from the gate circuit 1 of the amplitude modulation circuit is input to a series resonance circuit in which a coil L, a capacitor C6, and a semi-fixed variable resistor R4 are connected in series. The signal component of the reference frequency Fo of the amplitude modulation signal Vout resonates with the resonance circuit, so that the amplitude becomes Q (sharpness of resonance of the resonance circuit) times and then a sinusoidal amplitude modulation signal with the carrier frequency Fo. (Vrf in FIG. 2E) is output to the antenna ANT. Here, the setting of the intensity of the radio wave radiated from the antenna ANT can be changed by changing the value of the variable resistor R4 provided in the resonance circuit. The variable resistor R4 may be connected to any position of the series resonance circuit, or may be connected between the resonance circuit and the antenna ANT.
[0027]
As described above, according to the amplitude modulation circuit of the present embodiment, it is possible to configure the amplitude modulation circuit by using a general-purpose digital IC that is inexpensive and easily available, and has fewer adjustment points than the conventional circuit, and the number of parts. Therefore, the cost can be reduced. According to the transmitter including the amplitude modulation circuit, it is possible to efficiently transmit a sinusoidal amplitude modulation signal using the reference frequency component of the repetitive pulse signal Vosc as a carrier wave.
[0028]
In addition, the transmitter according to the present embodiment has its own position and traveling direction when a visually handicapped person or the like as proposed by the applicant in Japanese Patent Laid-Open No. 10-171343 moves alone in an urban area or facility. It is suitable for use as a transmission means in a position information guide device used for recognition. As described above, the variable resistance provided in the resonance circuit is adjusted to change the intensity of the radio wave transmitted from the transmitter, thereby changing the area where the position information guide device can inform the user's position and traveling direction. Can do.
[0029]
In the above embodiment, the pulse signal generation circuit 10 includes a pulse oscillation circuit 11 that generates a repetitive pulse signal repeated at an even number (A) times the reference frequency Fo, as shown in FIG. You may comprise using the frequency dividing circuit 12 which divides | segments the frequency of the output signal of the circuit 11 to 1 / A. The frequency dividing circuit 12 can be configured using a flip-flop circuit element (4013, 74HC74, etc.) as shown in FIG. When the pulse signal generation circuit 10 is configured using the pulse oscillation circuit 11 and the frequency dividing circuit 12 as described above, for example, the duty ratio of the repetitive pulse signal output from the pulse oscillation circuit 11 as shown in FIG. Even when the frequency is shifted from 50% to 33.3%, a repetitive pulse signal (Vosc) having a duty ratio adjusted to 50% is generated as shown in FIG. It can be input to the circuit 1. As a result, as shown in FIG. 6, the harmonic component that is an even multiple of the reference frequency Fo can be reduced, and an amplitude-modulated signal using the harmonic component of the reference frequency or an odd multiple of the reference frequency as a carrier wave is output. can do.
[0030]
In the above embodiment, the duty ratio of the repetitive pulse signal output from the pulse signal generation circuit 10 is shifted from 50%, and the amplitude modulation signal Vout output from the gate circuit 1 of the amplitude modulation circuit as shown in FIG. The ratio of harmonic signal components (2Fo, 4Fo,...) That is an even multiple of the reference frequency Fo included in may be increased. In this case, the resonance frequency of the resonance circuit 30 is set to one that is an even multiple of the reference frequency Fo. Thus, the resonance circuit 30 resonates with one of the multiples of the reference frequency Fo of the output signal Vout output from the gate circuit 1, so that the carrier frequency is the resonance frequency of the resonance circuit 30 and the amplitude is Q A sinusoidal amplitude-modulated signal that is double the sharpness of resonance of the resonance circuit 30 can be output to the antenna.
[0031]
In a conventional transmitter, in order to output a high-frequency amplitude modulation signal exceeding 20 MHz, an overtone signal having a frequency that is an integral multiple of the oscillation frequency output from the oscillation circuit is generated by the overtone circuit. Amplitude modulation was performed on the overtone signal. On the other hand, in the transmitter according to the present embodiment, high-frequency amplitude modulation is performed by using a resonance circuit to select harmonics from an amplitude-modulated rectangular wave signal that includes many harmonics of integer multiples without using the overtone circuit. A signal can be easily output.
[0032]
In the above embodiment, the output signal from the resonance circuit 30 is directly supplied to the antenna. However, a power amplifier is provided between the resonance circuit 30 and the antenna, and an amplitude modulation signal of desired power can be supplied to the antenna. You may comprise as follows. In particular, this power amplifier is preferably provided when a harmonic signal having a signal level lower than that of the fundamental wave is selected and supplied to the antenna.
[0033]
In the above embodiment, the gate circuit 1 is configured by connecting three NOT circuits in parallel. However, the number is not limited to this number, and one, two, or four or more are necessary. These NOT circuits may be combined. The gate circuit 1 may be configured using a basic gate circuit other than the NOT circuit. For example, as shown in FIG. 8, a circuit in which a plurality of NAND circuits each shorted on the input side are connected in parallel, or a flip-flop circuit can be used.
[0034]
In the above-described embodiment, a switching circuit constituted by an FET, a bipolar transistor, or the like that is available as a single unit instead of a digital IC may be used as the gate circuit 1. When such a transistor element such as a single FET or bipolar transistor is used, a high-power high-frequency switching circuit can be configured. Further, since the switching operation using the saturation region is performed, the element generates less heat than the analog circuit using the linear region under the same frequency region.
[0035]
【The invention's effect】
According to the first to fourth aspects of the present invention, it is possible to configure an amplitude modulation circuit using a general-purpose digital IC that is inexpensive and easily available, and has fewer adjustment points and fewer parts than the conventional circuit. Cost reduction is possible. In addition, there is an effect that it is possible to efficiently transmit a sinusoidal amplitude modulation wave signal using a harmonic signal component that is an even multiple of the reference frequency of the repetitive pulse signal output from the pulse signal generation circuit as a carrier wave .
[0036]
In particular, according to the present invention, the reference frequency signal leaked from the power supply voltage input terminal of the gate circuit can be bypassed to the ground side so as not to be input to the power supply voltage modulation circuit side. There is an effect that the frequency band of the modulation signal input to the circuit is not attenuated.
[0040]
In particular, according to the invention of claim 3 , there is an effect that a gate circuit composed of a high-power high-frequency switching circuit can be configured.
[0041]
In particular, according to the invention of claim 4 , there is an effect that an amplitude modulation signal having a desired output level can be obtained.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an amplitude modulation circuit according to an embodiment of the present invention.
FIG. 2A is an explanatory diagram showing a waveform of an input signal Vin input to a gate circuit of the same amplitude modulation circuit.
(B) is explanatory drawing which shows the waveform of the modulation signal Vm input into the power supply voltage modulation circuit of the same amplitude modulation circuit.
(C) is explanatory drawing which shows the waveform of the power supply voltage Vbm output from the power supply voltage modulation circuit of the same amplitude modulation circuit.
(D) is explanatory drawing which shows the waveform of the output signal Vout output from the gate circuit of the same amplitude modulation circuit.
(E) is explanatory drawing which shows the waveform of the amplitude modulation signal Vrf output from the transmitter provided with the same amplitude modulation circuit.
FIG. 3 is a circuit diagram showing a configuration example of a transmitter including the same amplitude modulation circuit.
FIG. 4A is a block diagram of a pulse signal generation circuit according to a modification.
FIG. 4B is an explanatory diagram of a flip-flop that constitutes the frequency dividing circuit of the pulse signal generation circuit.
FIG. 5A is an explanatory diagram showing a waveform of a signal input to the flip-flop.
(B) is explanatory drawing which shows the waveform of the signal output to the flip-flop.
FIG. 6 is an explanatory diagram showing a frequency spectrum of an output signal of an amplitude modulation circuit when a repetitive pulse signal with a duty ratio of 50% is input.
FIG. 7 is an explanatory diagram showing a frequency spectrum of an output signal of an amplitude modulation circuit when a repetitive pulse signal having a duty ratio shifted from 50% is input.
FIG. 8 is a circuit diagram of a gate circuit of an amplitude modulation circuit according to a modification.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Gate circuit 2 Power supply voltage modulation circuit 10 Pulse signal generation circuit 11 Pulse oscillation circuit 12 Frequency division circuit 20 Modulation signal generation circuit 30 Resonance circuit 40 Power supply circuit

Claims (4)

A pulse signal generation circuit that outputs a repetitive pulse signal repeated at a reference frequency;
A gate circuit that receives an input signal composed of a repetitive pulse signal that is repeated at the reference frequency and that is output from the pulse oscillation circuit, and an amplitude of the output signal that is output based on the input signal changes according to a power supply voltage and the gate An amplitude modulation circuit having a power supply voltage modulation circuit that changes a power supply voltage supplied to the circuit in accordance with a modulation signal ;
A modulation signal generation circuit that outputs a modulation signal input to the amplitude modulation circuit;
A resonance circuit that resonates at one of a reference frequency of the output signal of the amplitude modulation circuit or an integer multiple of the reference frequency;
A power supply circuit for outputting the power supply voltage,
The duty ratio of the repetitive pulse signal output from the pulse signal generation circuit is shifted from 50%,
The transmitter characterized in that the resonance frequency of the resonance circuit is set to one of an even multiple of the reference frequency . The transmitter of claim 1, wherein
An impedance element having a low impedance with respect to the reference frequency and a high impedance with respect to the frequency of the modulation signal is connected between the output terminal of the power supply voltage modulation circuit of the amplitude modulation circuit and the ground. Transmitter. In 請 Motomeko 1 or 2 of the transmitter,
A transmitter characterized in that the gate circuit of the amplitude modulation circuit is configured using a single transistor element. The transmitter according to any one of claims 1 to 3 ,
A transmitter comprising an amplifier circuit for amplifying an output signal output from the resonance circuit.

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