JPH09284055A - Fm demodulation method and fm demodulation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shape a pulse wave, to improve the S/N while being immune to power noise, ringing, waveform distortion and jitter, and to simplify the circuit. SOLUTION: An FM signal waveform is given to a waveform shaping circuit 1, from which a pulse shaped waveform is outputted, it is fed to an inverter of a logic integration circuit 2, from which an inverted pulse shaped waveform is outputted, the inverted pulse shaped waveform is given to an integration part of the logic integration circuit 2 consisting of a resistor and a capacitor, in which an unsharpened waveform is adjusted by adjusting the constant of the resistor and the capacitor and a resulting pulse wave is outputted. The pulse wave and the pulse shaped wave are given to an AND circuit 3, from which a triangular pulse wave whose peak voltage is close to a power supply voltage of the AND circuit 3 is outputted to a low pass filter 4, and a demodulation output is obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an FM demodulation method and an FM demodulation circuit for demodulating an FM signal.

[0002]

2. Description of the Related Art Conventionally, an FM demodulation circuit, which uses a delay circuit and obtains a constant pulse width for demodulation output, generally has a structure shown in FIG. That is, FIG. 3 is a block diagram showing a conventional FM demodulation circuit. In the figure, reference numeral 31 is a waveform shaping circuit for inputting an FM signal waveform and outputting a pulse shaping waveform, 36 is a delay circuit for delaying a pulse by a fixed time, and 37 is an anti-coincidence circuit for forming an exclusive OR.
An XOR circuit, 34 is a low-pass filter that cuts high-frequency components, integrates signal components, and outputs a demodulated wave, and 35 is an amplifier that amplifies the demodulated wave. In particular, for the delay circuit of 36, several logic ICs are stacked or a long wire is used.
Some circuits simply delay the pulse, which is the simplest circuit.

FIG. 4 is a diagram showing waveforms at a, b, and c in FIG. 4A is a diagram showing an output waveform (waveform at a) of the waveform shaping circuit 31 of FIG. 3, and FIG. 4B is a diagram showing an output waveform of the delay circuit 36 of FIG. 3 (waveform at b). 4 (c) is a diagram showing an output waveform (waveform at c) of the EXOR circuit 37 of FIG.

The input waveform of the FM signal is pulse shaped through the waveform shaping circuit 31 (FIG. 4A), and this is delayed by the delay circuit 36.
(FIG. 4B), and the waveform shaping circuit 31
2 and the output of the delay circuit 36 are input to the EXOR circuit 37 to output a waveform in which the pulse width is halved and the number of pulses is doubled (FIG. 4 (c)).
The high frequency component is cut by and the signal component is integrated to output a demodulated wave, which is amplified by the amplifier 35 and then output as a demodulated wave.

[0005]

The above-mentioned prior art has the following problems.

The first problem is that the S / N (signal to noise) ratio deteriorates due to power supply noise and ringing on the pulse waveform.

FIG. 5 is a diagram showing power supply noise and ringing on a waveform in a conventional FM demodulation circuit. In the figure, reference numeral 58 is power supply noise and 59 is ringing.

The demodulation circuit obtains a demodulation output by integrating the signal component of the pulse through a low pass filter. This time,
As shown in FIG. 5A, in a device with a poor power supply environment, power supply noise 58 is added to the pulse and similarly integrated and output. Also, as shown in FIG. 5B, ringing 59
Also affects and appears as a noise component.

A second problem is that when the S component is increased by widening the pulse width or increasing the number of pulses in order to improve the S / N ratio, the waveform is distorted and the FM wave bandwidth is increased. It means that there is a limit to the width (deviation).

FIG. 6 is a diagram showing waveform distortion in the conventional FM demodulation circuit. FIG. 6A is a diagram showing the density of pulses of a constant width when the FM wave has a narrow bandwidth.
(B) is a diagram showing a demodulated wave obtained by integrating the signal components of the pulse width of (a) with a constant width through a low-pass filter,
FIG. 6C is a diagram showing the density of pulses of a constant width when the FM wave has a wide bandwidth, and FIG. 6D shows the signal density of the pulses of a constant width of FIG. 6C through a low-pass filter. It is a figure which shows the demodulated wave obtained by integrating. In the figure, reference numeral 60 is a waveform distortion in the FM demodulation circuit of the conventional technique.

This kind of FM demodulation circuit obtains the waveform of FIG. 6B by integrating the signal component of the pulse density of a constant width as shown in FIG. 6A through a low pass filter. However, as shown in (c) of FIG. 6, when the bandwidth of the FM wave becomes wider, the number of dense pulses increases and the waveform becomes distorted like the waveform of (d) of FIG. This is the same even if the pulse width is widened.

The third problem is that the delay circuit includes a logic IC.
If a method of stacking a number of steps is used, the circuit scale can be small, but the S / N ratio is deteriorated due to the influence of jitter, and if the wire is lengthened to avoid the jitter and the delay is increased, the device scale becomes large. Is to be.

Especially when the frequency of the FM wave is high, I
Noise due to C jitter increases proportionally. Further, when a wire is used, there is no fear of noise such as jitter, but since the wire is usually a coaxial wire, it is bulky and the device becomes large.

In view of the above-mentioned problems of the prior art, an object of the present invention is to form a pulse wave which is not easily affected by power supply noise, ringing, waveform distortion and jitter and which improves the S / N ratio, and the circuit is simple. FM demodulation method and FM
It is to provide a demodulation circuit.

[0015]

According to the FM demodulation method of the present invention, in the FM demodulation method, an FM signal waveform is output as a pulse shaping waveform via a waveform shaping circuit, and the pulse shaping waveform is inverted pulse shaping via an inverter. The waveform is output, the inverted pulse shaping waveform is adjusted through the integrating circuit to adjust the resistance of the resistor and the capacitor to adjust the waveform bluntness, the pulse waveform is output, and the pulse waveform and the pulse shaping waveform are input to the AND circuit. A triangular pulse waveform close to the power supply voltage is output, and the triangular pulse waveform is demodulated through a low pass filter.

The FM demodulation circuit of the present invention is, in the FM demodulation circuit, a waveform shaping circuit which inputs an FM signal waveform and outputs a pulse shaping waveform, and an inverter which inputs a pulse shaping waveform and outputs an inverted pulse shaping waveform. , An inversion pulse shaping waveform is input, an integrator circuit that adjusts the waveform blunting by adjusting the constants of resistors and capacitors and outputs a pulse waveform, and a pulse waveform and a pulse shaping waveform are input, and the power supply voltage of the AND circuit is almost close. It has an AND circuit that outputs a triangular pulse waveform and a low-pass filter that inputs the triangular pulse waveform and obtains a demodulation output.

That is, the inverted pulse shaping waveform input to the integrator circuit is adjusted for the bluntness by adjusting the constants of the resistors and capacitors, and this waveform and the pulse shaping waveform output from the waveform shaping circuit are input to the AND circuit, The pulse wave output from the AND circuit forms a triangular pulse waveform that is substantially close to the power supply voltage of the AND circuit. Therefore, the power supply noise of the IC is not added and the ringing hardly occurs. Also,
Since the pulse width is narrow, the noise level of the demodulated wave due to the jitter is also small. Therefore, it is possible to form a waveform in which the influence of the power supply noise, ringing, and jitter on the S / N ratio can be minimized.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an FM demodulation circuit according to an embodiment of the present invention. In the figure, reference numeral 1 is a waveform shaping circuit, 2 is a logical integration circuit composed of an inverter and an integration circuit, 3 is an AND circuit for making a logical sum, 4 is a low-pass filter, and 5 is an amplifier.

The FM signal wave after the limiter amplifier is pulse-shaped through the waveform shaping circuit 1. After outputting the inverted pulse shaping waveform of this pulse shaping waveform through the inverter of the logical integration circuit 2, the output of the integration circuit and the output of the waveform shaping circuit 1 are input to the AND circuit 3 to generate a triangular waveform. Obtain the pulse waveform. This output waveform is demodulated via the low pass filter 4 and the amplifier 5.

Next, the operation of the embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

FIG. 2 is a diagram showing waveforms at a, b, and c in FIG. 2A is a diagram showing an output waveform (waveform at a) of the waveform shaping circuit 1 of FIG. 1, and FIG. 2B is a diagram showing FIG.
2 shows the output waveform of the logical integration circuit 2 (waveform in b), FIG. 2 (c) shows the output waveform of the AND circuit 3 in FIG. 1 (waveform in c), and FIG. 2 (d) shows in FIG. FIG. 6 is an enlarged view of an output waveform (waveform at c) of the AND circuit 3. In the figure, reference numeral 6 is a power supply voltage, and 8 is a power supply noise level.

FIG. 2A shows an output waveform of the waveform shaping circuit 1. This waveform is output as an inverted pulse shaping waveform through the inverter of the logical integration circuit 2 and then the constants of the resistor R and the capacitor C of the integration circuit. The waveform is blunted by, and a waveform as shown in FIG. The output of the waveform shaping circuit 1 and the output of the logical integration circuit 2 are input to the AND circuit 3, and the AND circuit 3
At, a pulse close to a triangular wave using the rising and falling of the pulse is shaped (FIG. 2 (c)). When this waveform is enlarged, it becomes as shown in FIG. This waveform has a level at which the peak reaches or does not reach the level of the power supply voltage 6, so that the power supply noise is not added and ringing does not appear. Further, since the pulse waveform close to the triangular wave has a narrow pulse width, even if the number of pulses is increased, the waveform is not distorted and the influence of jitter can be reduced.

[0024]

As described above, the present invention has the effect of forming a pulse wave which improves the S / N ratio and is less susceptible to power supply noise, ringing, waveform distortion and jitter.

Further, since the logical integration circuit corresponding to the delay circuit is simple and the parts used are small, the FM demodulation circuit can be simplified.

Further, the power supply circuit is simplified because it is not easily affected by the power supply noise and it is not necessary to remove the power supply noise.

That is, while improving the S / N ratio,
Since the circuit can be simplified, there is an effect that a small, lightweight, and inexpensive FM demodulator can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an FM demodulation circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing waveforms in a, b, and c of FIG. (A) It is a figure which shows the output waveform (waveform in a) of the waveform shaping circuit of FIG. (B) It is a figure which shows the output waveform (waveform in b) of the logic integration circuit of FIG. (C) It is a figure which shows the output waveform (waveform in c) of the AND circuit of FIG. (D) It is an enlarged view of the output waveform (waveform in c) of the AND circuit of FIG. 1.

FIG. 3 is a block diagram showing a conventional FM demodulation circuit.

FIG. 4 is a diagram showing waveforms at a, b, and c in FIG. (A) It is a figure which shows the output waveform (waveform in a) of the waveform shaping circuit of FIG. (B) Output waveform of the delay circuit in FIG. 3 (waveform in b)
FIG. (C) It is a figure which shows the output waveform (waveform in c) of the EXOR circuit of FIG.

FIG. 5 is a diagram showing power supply noise and ringing on a waveform in a conventional FM demodulation circuit. (A) It is a figure which shows the power supply noise on a waveform in the FM demodulation circuit of a prior art. (B) It is a figure which shows the ringing on a waveform in the FM demodulation circuit of a prior art.

FIG. 6 is a diagram showing waveform distortion in a conventional FM demodulation circuit. (A) It is a figure which shows the density of the pulse of a fixed width in case the bandwidth of FM wave is narrow. (B) It is a figure which shows the demodulated wave obtained by integrating the signal component of the density of the pulse of fixed width of (a) through a low pass filter. (C) It is a figure which shows the density of the pulse of a fixed width | variety when the band width of FM wave is wide. (D) It is a figure which shows the demodulated wave obtained by integrating the signal component of the density of the pulse of a fixed width of (c) through a low pass filter.

[Explanation of symbols]

 1, 31 Waveform shaping circuit 2 Logical integration circuit 3 AND circuit 4, 34 Low pass filter 5, 35 Amplifier 36 Delay circuit 37 EXOR circuit 58 Power supply noise 59 Ringing 60 Distortion

Claims (2)

[Claims] 1. In an FM demodulation method, an FM signal waveform is output as a pulse shaping waveform through a waveform shaping circuit, the pulse shaping waveform is output as an inverted pulse shaping waveform through an inverter, and the inverted pulse shaping waveform is output. A pulse waveform is output by adjusting the dullness of the waveform by adjusting the constants of the resistor and the capacitor through an integrating circuit, and the pulse waveform and the pulse shaping waveform are input to an AND circuit, and a triangle that is approximately close to the power supply voltage of the AND circuit. An FM demodulation method comprising outputting a wave-shaped pulse waveform and obtaining a demodulation output of the triangular wave-shaped pulse waveform through a low-pass filter. 2. In an FM demodulation circuit, a waveform shaping circuit which inputs an FM signal waveform and outputs a pulse shaping waveform, an inverter which inputs the pulse shaping waveform and outputs an inverted pulse shaping waveform, and the inverted pulse shaping An input circuit inputs a waveform, adjusts the waveform blunting by adjusting the constants of a resistor and a capacitor, and outputs a pulse waveform, and inputs the pulse waveform and the pulse shaping waveform.
An FM demodulation circuit comprising: the AND circuit which outputs a triangular pulse waveform close to the power supply voltage of the D circuit; and a low-pass filter which receives the triangular pulse waveform and obtains a demodulation output.