Comparator and voltage controlled oscillator circuit

• US 6,456,170 B1
• Filed: 03/30/2000
• Issued: 09/24/2002
• Est. Priority Date: 06/01/1999
• Status: Expired due to Term

• Current Assignee: Monterey Research, LLC (Vector Capital Corporation)
• Original Assignee: Fujitsu Limited
• Inventors: Segawa, Yuji, Kikuchi, Osamu, Yoshikawa, Yoshinori, Otsuka, Masaru, Haga, Akira
• Primary Examiner(s): KINKEAD, ARNOLD M
• Application Number:
  US09/538,720
• Time in Patent Office: 908 Days
• Field of Search: 331/111, 331/143, 331/57, 327/50, 327/54, 327/56, 327/57
• US Class Current: 331/143
• CPC Class Codes: H03K 19/0027 in field effect transistor circuits
• CPC Class Codes: H03K 2217/0018 Special modifications or use of the back gate voltage of a FET
• CPC Class Codes: H03K 3/0231 Astable circuits H03K3/0315 takes precedence
• CPC Class Codes: H03K 3/03 Astable circuits
• CPC Class Codes: H03K 3/0322 with differential cells
• CPC Class Codes: H03K 5/082 with an adaptive threshold
• CPC Class Codes: H03K 5/2481 with at least one differential stage
• CPC Class Codes: H03K 5/249 using clock signals

Abstract

The inverter functioning as a comparator, dummy inverter having the same electric characteristics as the inverter, and control circuit are provided. Vth detecting input voltage output from the control circuit is input into the dummy inverter, Vth detecting output voltage output from the dummy inverter is input into the control circuit, and the threshold voltage of the dummy inverter is detected. The threshold voltage of the inverter is controlled by controlling the back gate voltages of the MOS transistors of the dummy inverter and the inverter in such a manner that the threshold voltage of the dummy inverter coincide with an external reference voltage.

Claims

1. A comparator comprising:

an inverter which compares a voltage input from outside with a threshold voltage and outputs the result of the comparison as an output voltage;

a dummy inverter having a threshold voltage which is equal to or substantially equal to the threshold voltage of said inverter; and

a control circuit which detects the threshold voltage of said dummy inverter and based upon the result of this detection controls the threshold voltages of said inverter and said dummy inverter;

wherein said control circuit comprises;

an alternating current signal generator circuit which generates an alternating current signal and out puts the alternating current signal to said dummy inverter;

an internal comparator which compares the alternating current signal generated by said alternating current signal generator circuit with an external reference voltage; and

a differential amplifier circuit which outputs a difference between a direct current component of the output voltage of said internal comparator and a direct current component of the output voltage of said dummy inverter as a control signal for controlling the threshold voltages of said inverter and said dummy inverter.

2. A voltage controlled oscillator circuit comprising:

a first chopper comparator supplied with a reference voltage having a relatively high potential level, which first chopper comparator assuming a comparison operation state in response to a rise of a comparison voltage depending upon the input voltage and assuming an auto zero state in response to a fall of the comparison voltage;

a second chopper comparator supplied with a reference voltage having a relatively low potential level, which second chopper comparator assuming an auto zero state in response to a rise of the comparison voltage and assuming a comparison operation state in response to a fall of the comparison voltage; and

an output switching circuit which switches an output voltage from a first potential level to a second potential level in response to elapse of a delay time of said first chopper comparator after excess of the comparison voltage over the reference voltage of said first chopper comparator, and switches the output voltage from the second potential level to the first potential level in response to elapse of a delay time of said second chopper comparator after falling of the comparison voltage below the reference voltage of said second chopper comparator.

3. A voltage controlled oscillator circuit comprising:

a first chopper comparator supplied with a reference voltage having a relatively high potential level, which first chopper comparator assuming a comparison operation state in response to a rise of a comparison voltage depending upon the input voltage and assuming an auto zero state in response to a fall of the comparison voltage;

a second chopper comparator supplied with a reference voltage having a relatively low potential level, which second chopper comparator assuming an auto zero state in response to a rise of the comparison voltage and assuming a comparison operation state in response to a fall of the comparison voltage; and

an output switching circuit which switches the output voltage from a first potential level to a second potential level in response to elapse of a delay time of said first chopper comparator after excess of the comparison voltage over the reference voltage of said first chopper comparator, and switches the output voltage from the second potential level to the first potential level in response to elapse of a delay time of said second chopper comparator after falling of the comparison voltage below the reference voltage of said second chopper comparator;

wherein said first chopper comparator and said second chopper comparator are switched from the comparison operation state to the auto zero state and vice versa in synchronism with the voltage output from said output switching circuit.

4. A voltage controlled oscillator circuit comprising:

a first chopper comparator supplied with a reference voltage having a relatively high potential level, which first chopper comparator assuming a comparison operation state in response to a rise of a comparison voltage depending upon the input voltage and assuming an auto zero state in response to a fall of the comparison voltage;

a second chopper comparator supplied with a reference voltage having a relatively low potential level, which second chopper comparator assuming an auto zero state in response to a rise of the comparison voltage and assuming a comparison operation state in response to a fall of the comparison voltage;

an output switching circuit which switches an output voltage from a first potential level to a second potential level in response to elapse of a delay time of said first chopper comparator after excess of the comparison voltage over the reference voltage of said first chopper comparator, and switches the output voltage from the second potential level to the first potential level in response to elapse of a delay time of said second chopper comparator after falling of the comparison voltage below the reference voltage of said second chopper comparator; and

a logic circuit for generating a clock signal in synchronism with the voltage output from said output switching circuit;

wherein said first chopper comparator and said second chopper comparator are switched from the comparison operation state to the auto zero state and vice versa in synchronism with the voltage output from said output switching circuit;

wherein said clock signal being delayed by a predetermined time as compared with the voltage output from said output switching circuit, an operation state of said first chopper comparator being controlled by the clock signal, an operation state of said second chopper comparator being controlled by an inversion signal of the clock signal.

5. A voltage controlled oscillator circuit comprising:

a first chopper comparator supplied with a reference voltage having a relatively high potential level, which first chopper comparator assuming a comparison operation state in response to a rise of a comparison voltage depending upon the input voltage and assuming an auto zero state in response to a fall of the comparison voltage;

a second chopper comparator supplied with a reference voltage having a relatively low potential level, which second chopper comparator assuming an auto zero state in response to a rise of the comparison voltage and assuming a comparison operation state in response to a fall of the comparison voltage;

an output switching circuit which switches an output voltage from a first potential level to a second potential level in response to elapse of a delay time of said first chopper comparator after excess of the comparison voltage over the reference voltage of said first chopper comparator, and switches the output voltage from the second potential level to the first potential level in response to elapse of a delay time of said second chopper comparator after falling of the comparison voltage below the reference voltage of said second chopper comparator;

a current source;

a converter circuit which controls said current source so as to generate a current proportionate to the input voltage; and

a capacitor which is charged or discharged based on the current from said current source and generates the comparison voltage based on the charging or discharging;

wherein said first chopper comparator and said-second cropper comparator are switched from the comparison operation state to the auto zero state and vice versa in synchronism with the voltage output from said output switching circuit.