JPH0225106A - Waveform shaping circuit - Google Patents

Abstract

PURPOSE:To a void an amplitude level of an input signal from being affected by the duty of a shaped rectangular wave signal by limiting an output signal amplitude of an inverse amplifier to a constant level. CONSTITUTION:An FM modulation signal inputted to a terminal 11 is amplified by an inverse amplifier 13 via capacitor 12, waveform-shaped by inverse amplifiers 16, 17 into a rectangular wave and given to an FM demodulation circuit 18 of the pulse count system. An amplitude limit circuit 25 comprising diodes 22, 23 and a capacitor 24 is connected to the output terminal of the inverse amplifier 13 to limit the output signal level of the amplifier 13 to a constant level. Even if there is a difference in the characteristic of P and N channels of a CMOS circuit being a component of the amplifier 13, since the positive and negative waveforms of the output signal from the amplifier 13 are made nearly equal to each other, the average value of the output of the amplifier 13 is not fluctuated by the amplitude of the input signal and the bias voltage through a resistor 15 is made constant. Then the input signal amplitude is not affected by the duty cycle of the rectangular wave.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a waveform shaping circuit that shapes a sine wave signal into a rectangular wave signal with a constant amplitude, and particularly relates to a waveform shaping circuit that shapes a sine wave signal into a rectangular wave signal with a constant amplitude, and particularly relates to a waveform shaping circuit that shapes a sine wave signal into a rectangular wave signal with a constant amplitude. The present invention relates to a device suitable for use in an FM demodulation circuit, etc.

(Prior Art) As is well known, a pulse count type FM demodulation circuit using a waveform shaping circuit that shapes a sine wave signal into a rectangular wave signal with a constant amplitude is configured as shown in FIG. . A sinusoidal input signal (FM modulation signal) supplied to the input terminal 11 is supplied to the input terminal of the inverting amplifier 13 via the capacitor 12 and is inverted and amplified. At this time, the human-powered DC (direct current) bias voltage of the inverting amplifier 13 is
3 is fed back to the input terminal of the inverting amplifier 13 via the resistor 15 forming the feedback circuit 14.

The output of the inverting amplifier 13 is connected to the inverting amplifier 1 connected in series.
8.17 and shaped so that its rising and falling edges become rectangular waves. Then, the rectangular wave signal output from the inverting amplifier 17 is FM demodulated by the FM demodulation circuit 18 and taken out from the output terminal 19. Note that the inverting amplifiers 13, 16, and 17 are composed of P-channel and N-channel CMOS field effect transistors 2, as shown in FIG.
0.21 are interconnected.

FIG. 6 shows signal waveforms at various parts of the conventional waveform shaping circuit shown in FIG. FIG. 6(a) shows an input signal, and solid lines and dotted lines in the figure represent cases where the signal amplitude is small and large, respectively. The inverting amplifier 13 is a nonlinear amplifier because the P-channel and N-channel CMO3 field effect transistors 20 and 21 have different characteristics. Therefore, the output waveform of the inverting amplifier 13 is distorted as shown by the solid line and the dotted line in FIG. 6(b), respectively, depending on whether the input signal amplitude is small or large.

On the other hand, the DC bias voltage generated at the input of the inverting amplifier 13 matches the output voltage of the inverting amplifier 13 when there is no signal. However, when a signal is present, the output signal of the inverting amplifier 13 is smoothed by the capacitor 12 and the resistor 15, and for example, when the amplitude is small due to manual input, the upper and lower areas are equal as shown by diagonal lines in FIG. 6(b). Stabilizes to level no.

At this time, there would be no problem if the inverting amplifier 13 had linear characteristics, but in reality it has non-linear characteristics as described above, so when the input amplitude is large, the DC bias voltage generated at the input of the inverting amplifier 13 is The level at which the areas become equal is stable at level No. 2, which is lower than the above-mentioned level No. 1, as shown in FIG. 6(b).

That is, the DC bias voltage generated at the input of the inverting amplifier 13 varies depending on whether the input signal amplitude is small or large. Therefore, the pulse width of the rectangular wave signal obtained by shaping the output of the inverting amplifier 13 by the inverting amplifiers 16 and 17 is shown by the solid line and dotted line in FIG. 6(C) when the input signal amplitude is small and when the input signal amplitude is large. As shown, they differ, that is, the duty fluctuates.

This results in phase fluctuations, and fluctuations in the input signal amplitude (AM component), which should originally be unrelated to FM demodulation, affect the FMI modulation output.

Particularly, in the FM modulation output of the HlFi audio signal in a two-head type high quality (HlFi) video tape recorder, variations in the characteristics of the two audio heads directly appear as the amplitude of the FM modulation signal. in this case,
When the above-mentioned duty fluctuation of the rectangular wave signal occurs due to the amplitude difference between the FM modulation signals obtained from both heads, a problem arises in that this duty fluctuation becomes noise and is mixed into the reproduced audio.

(Issue 8 to be solved by the invention) As described above, in the conventional waveform shaping circuit, the duty of the shaped rectangular wave signal fluctuates depending on the magnitude of the input signal amplitude. When used in the front stage, there is a problem in that it causes noise in the FM demodulated signal.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an extremely good waveform shaping circuit in which the duty of a shaped rectangular wave signal is not affected by the amplitude level of an input signal.

[Structure of the Invention] (Means for Solving the Problems) The present invention comprises a capacitor to which a sinusoidal input signal is supplied at one end, an inverting amplifier to which the other end of the capacitor is connected to the input end, and an inverting amplifier to which a sinusoidal input signal is supplied. This waveform shaping circuit includes a feedback circuit that returns the output of the amplifier to the input side and shapes an input signal into a rectangular wave signal, and is configured to limit the output signal amplitude of the inverting amplifier to a constant level.

(Function) According to the above configuration, since the output signal amplitude of the inverting amplifier is limited to a constant level, the level component of the signal fed back via the feedback circuit is always constant, and the level component generated at the input of the inverting amplifier is Since the DC bias voltage can be kept constant, the duty of the shaped rectangular wave signal is not affected by the amplitude level of the human input signal. Note that if the limit on the output signal amplitude of the inverting amplifier is set to be vertically symmetrical with respect to the DC bias voltage when there is no signal, the duty of the rectangular wave signal can be maintained at 50%.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as in FIG. 4 are indicated with the same symbols, and only the different parts will be described here. That is, an amplitude limiting circuit 25 consisting of diodes 22, 23 and a capacitor 24 connected in parallel in opposite directions is connected to the output terminal of the inverting amplifier 13, so as to limit the output signal amplitude of the inverting amplifier 13 to a constant level. What we did is different from the conventional method.

According to the above configuration, when the input signal amplitude is small and large as shown by the solid line and dotted line in FIG. 2(a),
It can be seen that distortion in the output of the inverting amplifier 13 is almost completely removed, as shown by solid lines and dotted lines in FIG.

The amount of distortion removed is equal to the input signal amplitude 1 inverting amplifier 1
It is determined by the gain of 3, the limiting level by the amplitude limiting circuit 25, etc., and it is sufficient that the amplitude limiting level is sufficiently lower than the output level of the inverting amplifier 13.

Therefore, the level of the output of the inverting amplifier 13 smoothed by the capacitor 12 and the resistor 15, that is, the DC bias voltage, can be kept constant. Therefore, the inverting amplifier 1
The duty of the rectangular wave signal obtained by shaping the output waveform of No. 3 by the inverting amplifier 18 and 17 is no longer affected by the amplitude level of the input signal, as shown in FIG. 2(C).

Furthermore, if the amplitude limiting level by the amplitude limiting circuit 25 is set to be symmetrical in the upper and lower (positive and negative) directions with respect to the DC bias voltage when there is no signal, the inverting amplifier 13
Since the output of is always equal in area above and below the DC bias voltage level when there is no signal, the duty of the rectangular wave signal can be set to 50%.

FIG. 3 shows another embodiment of the invention, in which the output of the inverting amplifier 17 is fed back to the input of the inverting amplifier 13 via a resistor 15. In this embodiment, the inverting amplifier 17 itself is considered as an amplitude limiting circuit, and the amplitude is limited by the power supply voltage vCC and the ground level.

It should be noted that the present invention is not limited to the above-described embodiments, and can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to provide an extremely good waveform shaping circuit in which the duty of the shaped rectangular wave signal is not affected by the amplitude level of the input signal.

[Brief explanation of the drawing]

1 and 2 are block circuit configuration diagrams showing one embodiment of the present invention and waveform diagrams for explaining its operation, and FIG. 3 is a block circuit configuration diagram showing another embodiment of the invention, FIG. 4 is a block circuit configuration diagram showing a conventional waveform shaping circuit, FIG. 5 is a circuit configuration diagram showing a specific configuration of an inverting amplifier, and FIG. 6 is a waveform diagram for explaining the operation of the conventional circuit. be. 11...Input terminal, 12...Capacitor, 13...
・Inverting amplifier, 14... Feedback circuit, 15... Resistor,
18.17... Inverting amplifier, 18... FM demodulation circuit, 19... Output terminal, 20゜21... CMOS field effect transistor, 22.2 (... Diode, 24... Capacitor , 25... Amplitude limiting circuit. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure Figure Figure Figure Figure

Claims (1)

[Claims] a capacitor to which a sinusoidal input signal is supplied;
A waveform shaping circuit for shaping the input signal into a rectangular wave signal, comprising an inverting amplifier in which the other end of the capacitor is connected to the input end, and a feedback circuit for feeding back the output of the inverting amplifier to the input side. 1. A waveform shaping circuit comprising amplitude limiting means for limiting the output signal amplitude of an inverting amplifier to a constant level.