Waveform shaping circuit

• US 5,548,242 A
• Filed: 04/08/1994
• Issued: 08/20/1996
• Est. Priority Date: 04/12/1993
• Status: Expired due to Term

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Yasuda, Yukio, Ohashi, Yutaka
• Primary Examiner(s): Callahan, Timothy P.
• Assistant Examiner(s): LE, DINH THANH
• Application Number:
  US08/224,885
• Time in Patent Office: 865 Days
• Field of Search: 327/551, 327/552, 327/559, 327/557, 327/510, 327/513, 327/558, 327/100, 307/652, 307/650, 342/166, 342/174, 330/9, 330/261, 330/258
• US Class Current: 327/559
• CPC Class Codes: H03K 5/08 by limiting; by thresholding; by slicing, i.e. combined limiting and thresholding H03K5/07 takes precedence; comparing one pulse with another H03K5/22; providing a determined threshold for switching H03K17/30

Abstract

A waveform shaping circuit shapes a waveform by comparing an output signal generated by an electromagnetic coil in response to a change in an incident magnetic flux to a reference voltage in a comparator. The circuit prevents waveform shaping error due to rapid fluctuations in the output signal. The waveform shaping circuit includes a high-pass filter that removes low-frequency components having frequencies not higher than a cut-off frequency from the output signal of the electromagnetic coil and that has at least two different attenuation characteristics with respective cut-off frequencies, a voltage limiting circuit for switching between the attenuation characteristics of the filter in response to the amplitude of the output signal of the electromagnetic coil by limiting the amplitude of the output signal to a maximum voltage, and a comparator for comparing the filtered output signal with a reference voltage and generating a shaped output signal in response.

Claims

1. The waveform shaping circuit comprising:

an electromagnetic coil for generating an AC output signal that varies in amplitude in response to a change in an incident magnetic flux;

filter means coupled to said electromagnetic coil for removing low-frequency components having frequencies not higher than a cut-off frequency from the AC output signal of said electromagnetic coil, said filter means producing a filtered output signal and comprising;

a first high-pass filter coupled to said electromagnetic coil and said voltage limiting circuit and having a first attenuation characteristic for removing low-frequency components having frequencies not higher than a first cut-off frequency from the AC output signal of said electromagnetic coil, said first high-pass comprising a first resistor, a first capacitor, and a second resistor connected in series, said first resistor, first capacitor, and second resistor connected in series being connected in parallel with said electromagnetic coil; and

a second high-pass filter coupled to said electromagnetic coil and said voltage limiting circuit and having a second attenuation characteristic for removing low-frequency components having frequencies higher than the first cut-off frequency and lower than a second cut-off frequency, the second cut-off frequency being higher than the first cut-off frequency, from the AC output signal of said electromagnetic coil, said second high-pass filter comprising a third resistor and a second capacitor connected in series, said third resistor and second capacitor being connected in parallel with said first resistor;

a voltage limiting circuit coupled to said electromagnetic coil and said filter means for switching between the attenuation characteristics of said filter means in response to the amplitude of the AC output signal of said electromagnetic coil by limiting the amplitude of the AC output signal of said electromagnetic coil so that the AC output signal does not exceed a maximum voltage; and

a comparator having first and second input terminals for comparing the filtered output signal with a reference voltage and generating a shaped output signal in response, a node connecting said first capacitor to said second resistor being connected to the first input terminal of said comparator and a node connecting said electromagnetic coil to said second resistor being connected to the second input terminal of said comparator.

2. The waveform shaping circuit according to claim 1 wherein said voltage limiting circuit comprises a pair of diodes connected to each other in reverse polarity and in parallel with said series-connected first capacitor and second resistor.

3. The waveform shaping circuit according to claim 1 wherein the capacitance of said second capacitor is less than the capacitance of said first capacitor.

4. A waveform shaping circuit comprising:

an electromagnetic coil for generating an AC output signal that varies in amplitude in response to a change in an incident magnetic flux;

filter means coupled to said electromagnetic coil for removing low-frequency components having frequencies not higher than a cut-off frequency from the AC output signal of said electromagnetic coil, said filter means producing a filtered output signal and comprising;

a first high-pass filter coupled to said electro-magnetic coil and said voltage limiting circuit and having a first attenuation characteristic for removing low-frequency components having frequencies not higher than a first cut-off frequency from the AC output signal of said electromagnetic coil, said first high-pass filter comprising a first resistor, a first capacitor, and a second resistor connected in series, said first resistor, first capacitor, and second resistor connected in series being connected in parallel with said electromagnetic coil;

a second high-pass filter coupled to said electro-magnetic coil and said voltage limiting circuit and having a second attenuation characteristic for removing low-frequency components having frequencies higher than the first cut-off frequency and lower than a second cut-off frequency, the second cut-off frequency being higher than the first cut-off frequency, from the AC output signal of said electromagnetic coil, said second high-pass filter comprising a third resistor and a second capacitor connected in series, said third resistor and second capacitor connected in series being connected in parallel with said first resistor; and

a third high-pass filter coupled to said electromagnetic coil and said second high-pass filter and having a third cut-off frequency higher than the second cut-off frequency, said third high-pass filter comprising a fourth resistor and a third capacitor connected in series, said fourth resistor and third capacitor connected in series being connected in parallel with said third resistor;

a voltage limiting circuit coupled to said electromagnetic coil and said filter means for switching between the attenuation characteristics of said filter means in response to the amplitude of the AC output signal of said electromagnetic coil by limiting the amplitude of the AC output signal of said electromagnetic coil so that the AC output signal does not exceed a maximum voltage; and

a comparator having first and second input terminals for comparing the filtered output signal with a reference voltage and generating a shaped output signal in response, a node connecting said first capacitor to said second resistor being connected to the first input terminal of said comparator and a second node connecting said electromagnetic coil to said second resistor being connected to the second input terminal of said comparator.

5. The waveform shaping circuit according to claim 4 wherein said voltage limiting circuit comprises a pair of diodes connected to each other in reverse polarity and in parallel with said series-connected first capacitor and second resistor.

6. The waveform shaping circuit according to claim 4 wherein the capacitance of said second capacitor is less than the capacitance of said first capacitor.