JP2000077947A - Oscillation detection circuit and am receiver provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an oscillation detection circuit which enables high fidelity demodulation of, especially an SSB(single side band) wave and also has noise elimination effects. SOLUTION: In this oscillation circuit which is provided with an amplifying part 2, a tuning part 1 that is connected to the preceding stage of the amplifying part and a feedback part 3 which applies feedback from an output of the amplifying part through the tuning part and oscillates in a tuning frequency of the tuning part, when an amplitude modulation wave is applied to an input of the tuning part, the oscillation circuit oscillates in a carrier frequency of the amplitude modulation wave in a slave manner and a half-wave rectification wave of the amplitude modulation wave in which a carrier is added to an input signal and a modulation degree drops is obtained at an output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a technique for demodulating an amplitude-modulated wave.

[0002]

2. Description of the Related Art A technique relating to demodulation of an amplitude-modulated wave is described in Document 1, "Wireless Communication Equipment", Japan Science and Technology Press (1991).
, Pages 212 to 220, describes an envelope detection method and a synchronous detection method, and describes SSB (Single Side
e Band) demodulation is described on pages 228 to 233. Also, Reference 2, Iwao Negishi: "Basic Knowledge of Radio", Seibundo Shinkosha, p. 289 (1954), there is a zero-beat method (homodyne) as a special receiving method of a reproduction receiver. A method is described in which the oscillating frequency is set to an oscillating state and the oscillating frequency is made substantially coincident with the frequency of the incoming radio wave so that no beat sound is generated.

[0003]

The prior art is described in detail in the above-mentioned literature, but the envelope detection method in the literature 1 has clipping distortion.
The synchronous detection method has a complicated circuit configuration and SSB.
The demodulation method of (Single Side Band) has problems that the circuit configuration is complicated and distortion occurs because the transmission frequency of the SSB does not match the carrier frequency for demodulation. The method described in 2 has good sensitivity, but lacks clarity of the received sound, and has a problem that it is hardly used except in a special case such as reception of a very weak radio wave at a long distance or a carrier removal method of transmitting a carrier wave. . The conventional demodulation method does not have the noise reduction effect as in the present invention. Accordingly, an object of the present invention is to provide an oscillation detection circuit which eliminates the drawbacks of the conventional amplitude modulation wave demodulation method, in particular, enables high-fidelity demodulation of SSB waves, and also has a noise reduction effect, and an oscillation detection circuit having the same. No AM receiver is provided.

[0004]

In order to achieve this object, an oscillation detection circuit according to the present invention comprises an amplifying section, a tuning section connected in front of the amplifying section, and an output from the amplifying section via the tuning section. An oscillation circuit oscillating at a tuning frequency of the tuning unit, wherein when the amplitude modulation wave is applied to the input of the tuning unit, the oscillation circuit operates as a carrier of the amplitude modulation wave. It oscillates as a slave at a frequency, and a carrier is added to the input signal at the output, and a half-wave rectified wave of the amplitude-modulated wave whose modulation degree is reduced is obtained, so that high-fidelity demodulation can be obtained. It is assumed that.

In a preferred embodiment of the circuit according to the present invention, a differential amplifying unit for differentiating an output signal of the detection circuit to narrow a flow angle and simultaneously increase a modulation degree, and clocking a carrier of the output signal of the detection circuit by a clock. A frequency divider is operated as a pulse, and a sampling pulse generating unit that generates a sampling pulse by differentiating and shaping a square wave of a frequency divider output, and a carrier of an output signal of the differential amplifying unit is switched by the generated sampling pulse. And a carrier thinning section for thinning the number of the carriers, so as to reduce noise in the output of the detection circuit.

Further, an AM receiver according to the present invention is characterized in that the oscillation detection circuit according to the present invention or the preferred embodiment is used as an intermediate frequency conversion circuit.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention focuses on the fact that an oscillation circuit has a function of demodulating an amplitude-modulated wave, and improves and commercializes it. For example, when a tuning unit is connected to the input of an amplification unit composed of two transistors, and feedback is applied from the output via the tuning unit, the amplification unit oscillates at the tuning frequency. When the amplitude modulation wave is applied to the input while the oscillation intensity is adjusted to an appropriate level by changing the feedback amount, the circuit oscillates at the frequency of the input signal, and the carrier is added to the input signal at the output, reducing the modulation degree The obtained half-wave rectified wave is obtained. That is, the amplitude modulation wave is demodulated.

Further, an operation of thinning out the carrier by sampling the demodulated signal is performed. Since the noise is superimposed on the carrier, the noise is reduced by thinning out the carrier. In the embodiment, 15 carriers out of 16 carriers are thinned out and demodulated by sampling by dividing the carrier by 16. In the case of AM radio, the maximum value of the modulation frequency is 9 kHz and the carrier frequency is 531 to 1629 kHz.
When the frequency is divided by 16, the frequency is 33.2 kHz, which is three times or more than 9 kHz. Therefore, the voice modulation signal can be demodulated. A feature of the oscillation detection circuit of the present invention is that high-fidelity detection is performed because demodulation is performed with a reduced modulation factor. No clipping distortion occurs unlike the conventional envelope detection method. Has a noise reduction function. The conventional envelope detection method and synchronous detection method have almost no noise reduction function. BSB (Both Side Band), SSB
Regardless of the (Single Side Band) method, it is possible to demodulate an amplitude modulated wave in any mode. Since the present invention uses the slave oscillation method, the oscillation component is added to the input signal as a carrier, so that high-fidelity demodulation can be performed even with SSB. The circuit configuration is very simple and can be realized at low cost. Because of the above features, the oscillation detection circuit of the present invention is considered to be applied to various aspects.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows a schematic configuration diagram of the oscillation detection circuit of the present invention. This circuit includes a tuning unit 1, an amplifying unit 2, and a feedback unit 3, and constitutes a slave oscillation circuit that oscillates following an input signal.

In a case where the oscillation amount is changed to an appropriate level by changing the feedback amount of the oscillation circuit, when an amplitude modulated wave is applied to the input, the circuit oscillates at the carrier frequency of the input signal.
At the output, a half-wave rectified wave of the amplitude-modulated wave with a reduced modulation factor appears. In other words, this shows that the slave oscillation circuit has a function of demodulating the amplitude modulated wave. The circuit shown in FIG. 2 was produced as a specific example of FIG. 1, and its operation was confirmed. FIG. 2 shows two transistors Tr ₁ and Tr ₂ (both 2S).
The tuning section of L (inductance element) and C (capacitance element) is connected to the amplification section constituted by C1815).
Since there is a gain of 50 times between the base input of Tr ₁ and the collector output (d) of Tr ₂ and (b) and (d) have the same phase, from (d) through R, L, C When feedback is applied to this amplifier, the circuit oscillates at the L and C resonance frequencies. When a signal is input to this input terminal (a) and tuning is performed, the amplifier follows an input signal and oscillates (slave oscillation).
Will do.

[0011] oscillation intensity can be controlled by increasing or decreasing the resistance of the feedback resistor R, based case Tr ₁ of the oscillation intensity appropriate value (b) and Tr ₁ collector (c)
A half-wave rectified wave in which the information of the input signal is added to the oscillation component appears at the collector (d) of Tr ₂ . From this, the input signals are BSB (Both Side Band), S
Regardless of SB (Single Side Band),
It can be seen that demodulation can be performed regardless of the mode of the amplitude modulation wave. In this example, it was confirmed that BSB and SSB can be demodulated with high fidelity.

The operation of each section will be described with reference to the waveforms shown in FIG. 3. Waveform (a) is an input signal of (a), and has a carrier frequency of 594 kHz, a modulation frequency of 1 kHz, a modulation factor of 95%, and a voltage of 0.1 Vpp. With this input signal, the circuit
Oscillates at 94 kHz. At the Tr ₁ base input (b) of the waveform (b), a half-rectified wave appears in which the oscillation component is added to the input signal in the same phase and the degree of modulation is reduced to 50%.
This is a waveform equivalent to synchronous detection.) This degree of modulation is the case where the feedback resistance R is 1 KΩ. When R is 1 KΩ or more, the oscillation is weakened and the degree of modulation increases, and when it is 1 KΩ or less, the degree of modulation decreases. A half-wave rectified wave in which the signal of the waveform (b) is amplified and the degree of modulation is reduced to 5% appears on the collector output (c) of the Tr ₁ of the waveform (c). The waveform (d) is Tr
This is fed back to the input with the waveform of the collector output (d) of ₂ .

If the outputs of the waveforms (b) and (c) are passed through a low-pass filter, an audio signal having a low distortion rate is demodulated because the degree of modulation is reduced. Further, the signal of the waveform (c) is output, and noise is reduced by a sampling amplifier circuit described below.
Here, in each of the waveforms (a) to (d) shown in FIG. 3, the left waveform is a 594 kHz carrier waveform (peak interval 1.68 μs).
ec), and note that the waveform on the right side shows the envelope waveform (peak interval 1 msec) of the modulated wave of 1 kHz. FIG. 4 shows a schematic configuration diagram of the sampling amplifier circuit. This circuit intends to achieve noise reduction by narrowing the distribution angle of a signal wave and thinning out carriers by sampling.

The differential amplifying unit 5 shown in FIG. 4 performs an operation of differentiating the output signal of the oscillation detection circuit 4 to narrow the flow angle and increase the modulation degree. The sampling pulse generator 6 is a circuit that operates the frequency divider using the output signal of the oscillation detection circuit 4 as a clock pulse, and generates a sampling pulse by differentiating and shaping the square wave output from the frequency divider. Further, the carrier thinning section 7 performs an operation of thinning out the number of carriers by switching the differentially amplified signal with a sampling pulse.

The operation of this circuit will be described with reference to a specific embodiment shown in FIG. The oscillation detection circuit 4 shown in FIG.
(C) is input. This is an amplitude modulated wave having a modulation factor of 5% and an amplitude of 4.5V. This signal is transferred to the capacitor C
₁ (6 to 120 pF) and the resistance R ₁ (3 KΩ) to narrow the flow angle, and the transistor Tr ₃ (2SC1815)
(The modulation is increased because Tr ₃ is operated with a negative bias), and a resistor R ₂ (1 KΩ) and a capacitor C
₂ By integrating at (1000 pF), a waveform at the position (e) is obtained. The reason for integrating a resistor R ₂ and capacitor C ₂ is to widen the distribution angle narrowed by differentiating again. In the waveform at the position (e), the input modulation degree 5% is 50%.
To rise.

On the other hand, the input signal (c) is input to the frequency dividing IC (74HC4040) as a clock signal.
A square wave divided to 1/16 of (f) is extracted. (C)
Is subjected to 5% amplitude modulation, but with such a degree of modulation, it can be used as a clock signal and the frequency dividing IC does not malfunction.

The signal of (f) is converted to a capacitor C ₃ (6 to 12).
0 pF) and the resistance R ₃ (20 kΩ), and Tr ₅ (2
SC1815), the sampling pulse of (g) is obtained. Tr ₆ (2SC1815) is driven by this sampling pulse (g), and Tr ₄ (2S1815) is driven.
After switching K241), Tr ₇ (2SC18)
When amplified in 15), the output signal of (h) is obtained.

The signal of (h) is 15 out of 16 carriers.
This is a pulse-like waveform in which books are thinned out and the distribution angle is extremely narrow, and a modulation component is stored in this.

The carrier frequency of AM radio is 531 to 1
629 kHz, which is 1 / of the lowest frequency 531 kHz.
16 is 33.2 kHz. Since the maximum value of the audio frequency to be modulated is 9 kHz, 33.2 kHz is three times or more thereof, so that demodulation can be performed using one of the 16 carriers.

The noise reduction effect of the signal (h) is as shown in the waveform, with a duty ratio of 26.9 μsec: 50n.
sec ≒ 540: 1, which means that the signal passes only in 1/540 of the entire period. Assuming that the noise reduction effect on external noise is equal to the duty ratio, an effect of 50 dB (20 log 540 = 54.7 dB) or more can be obtained. Here, the signals (e ') and (h') shown in FIG. 6 are enlarged views of the signals (e) and (h) above.

Next, FIG. 7 shows a schematic configuration diagram of a noise reduction mixer circuit. Under the policy that noise reduction can be obtained by narrowing the distribution angle of the signal wave, this is to be applied to a mixer circuit. As shown in FIG.
1, the switching unit 13 and the local oscillation unit 12 are existing, but a new idea is to narrow the distribution angle of the signal wave by the differential amplification unit 14.

A specific embodiment will be described with reference to FIG. Tr₁₁When
Tr₁₂(Both 2SC1815) is an amplifier circuit. Entering
594 kHz, 95% modulation, level-4
A signal of 0 dBm is input. Tr ₁₃And Tr₁₄(Tomo
2SC1815) constitutes a CR oscillation circuit and 1044
It oscillates at kHz and the waveform is as shown in (m). (M)
With the waveform of Tr₁₂By switching the emitter of
And mixes the input signal with the signal of the oscillator.

The signal having the waveform (m) is converted to C ₁₁ (6 to 120 p
F) and R ₁₁ (1 kΩ), differentiated and amplified by Tr ₁₆ and Tr ₁₇ (both 2SC1815), an output signal of the waveform (n) is obtained. In the waveform (n), the frequency component 594 kHz of the input signal and the frequency component 104
4kHz, frequency converted 450kHz, 1638k
Hz (1044 ± 594 kHz) and the like, and the intensity thereof is equal to the level (−40 dBm) of the input signal as shown by the spectrum waveform (n ′).

If the signal (n) is passed through a 594 kHz tuning circuit, 594 kHz is obtained, and if it is passed through a 450 kHz tuning circuit, a 450 kHz signal is obtained. As shown in the output waveform of (n), the duty ratio is 32: 1 by the differential amplifier circuit.
Since the signal passes only for a period of 1/32, a noise reduction effect of 30 dB against external noise can be expected.

Although the embodiments of the present invention have been described in detail with reference to several embodiments, the present invention is not limited to these embodiments, and various modifications can be made within the scope of the invention. It is self-evident.

[0026]

Since the oscillation detection circuit of the present invention uses the slave oscillation method, the oscillation component is added to the input signal as a carrier, so that high fidelity demodulation can be performed even with SSB. There are advantages that clipping distortion does not occur unlike the conventional envelope detection method (having a deep modulation degree), and there is a noise reduction function.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an oscillation detection circuit according to the present invention.

FIG. 2 is a circuit diagram of a specific embodiment of the circuit shown in FIG. 1;

FIG. 3 is a waveform diagram of each part of the circuit shown in FIG. 2;

FIG. 4 is a schematic block diagram of a sampling amplifier circuit according to the present invention.

FIG. 5 is a circuit diagram of a specific example of the circuit shown in FIG. 4;

FIG. 6 is a waveform diagram of each part of the circuit shown in FIG. 5;

FIG. 7 is a schematic block diagram of a noise reduction mixer circuit according to the present invention.

FIG. 8 is a circuit diagram of a specific example of the circuit shown in FIG. 7;

FIG. 9 is a waveform diagram of each part of the circuit shown in FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tuning part 2,11 Amplification part 3 Feedback part 4 Oscillation detection circuit 5,14 Differential amplification part 6 Sampling pulse generation part 7 Carrier thinning part 12 Oscillation part 13 Switching part

Claims (3)

[Claims] 1. An amplifier, a tuning unit connected to a preceding stage of the amplifier, and a feedback unit for performing feedback from an output of the amplifier via the tuning unit, wherein a tuning frequency of the tuning unit is provided. When an amplitude modulated wave is applied to the input of the tuning unit, the oscillation circuit oscillates as a slave at the carrier frequency of the amplitude modulated wave, and the carrier is added to the input signal at the output. An oscillation detection circuit configured to obtain a half-wave rectified wave of the amplitude-modulated wave having a reduced modulation degree and to obtain a high-fidelity demodulation. 2. A differential amplifier for differentiating an output signal of the detection circuit to narrow a flow angle and simultaneously increase a modulation degree, and operating a frequency divider using a carrier of the output signal of the detection circuit as a clock pulse, A sampling pulse generating unit for generating a sampling pulse by differentiating a square wave of a frequency divider output; and a carrier thinning unit for switching the number of carriers by switching the carrier of the output signal of the differential amplifying unit with the generated sampling pulse. 2. The oscillation detection circuit according to claim 1, further comprising: reducing an output noise of the detection circuit. 3. An oscillation detection circuit according to claim 1, wherein the oscillation detection circuit according to claim 1 is used as an intermediate frequency conversion circuit.
M receiver.