Low-pass filter, constant voltage circuit, and semiconductor integrated circuit including same
First Claim
1. A low-pass filter that filters an input signal input to a filter input terminal to output a filtered output signal to a filter output terminal, the low-pass filter comprising:
- a capacitor connected between the filter output terminal and ground;
a first field-effect transistor having a gate terminal, a first conduction terminal connected to the filter input terminal, and a second conduction terminal connected to the filter output terminal;
a first resistor connected between the gate and first conduction terminal of the first transistor; and
a first current source connected to the first resistor to supply a first current to the first resistor,the first resistor generating a first voltage thereacross based on the supplied first current for electrically biasing the gate terminal of the first transistor,wherein the first current source includes;
a second current source to supply a second current;
a second field-effect transistor having a gate terminal, a first conduction terminal connected to the gate terminal thereof, and a second conduction terminal connected to the second current source,the second transistor generating a second voltage at the second conduction terminal thereof based on the second current supplied from the second current source;
a second resistor;
a third field-effect transistor having a gate terminal, a first conduction terminal connected to the first resistor, and a second conduction terminal connected to the second resistor,the third transistor conducting the first current between the first and second conduction terminals thereof for supply to the first resistor in response to a control signal applied to the gate terminal thereof,the second resistor generating a third voltage at the second conduction terminal of the third transistor conducting the first current; and
an operational amplifier having a first input connected to the second conduction terminal of the second transistor, a second input connected to the second conduction terminal of the third transistor, and an output connected to the gate terminal of the third transistor to output the control signal to the gate terminal of the third transistor so as to maintain the third voltage substantially equal to the second voltage.
4 Assignments
0 Petitions
Accused Products
Abstract
A low-pass filter that filters an input signal input to a filter input terminal to output a filtered output signal to a filter output terminal includes a capacitor, a first field-effect transistor, a first resistor, and a first current source. The capacitor is connected between the filter output terminal and ground. The first field-effect transistor has a gate terminal, a first conduction terminal connected to the filter input terminal, and a second conduction terminal connected to the filter output terminal. The first resistor is connected between the gate and first conduction terminals of the first transistor. The first current source is connected to the first resistor to supply a first current to the first resistor. The first resistor generates a first voltage thereacross based on the supplied first current for electrically biasing the gate terminal of the first transistor.
18 Citations
13 Claims
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1. A low-pass filter that filters an input signal input to a filter input terminal to output a filtered output signal to a filter output terminal, the low-pass filter comprising:
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a capacitor connected between the filter output terminal and ground; a first field-effect transistor having a gate terminal, a first conduction terminal connected to the filter input terminal, and a second conduction terminal connected to the filter output terminal; a first resistor connected between the gate and first conduction terminal of the first transistor; and a first current source connected to the first resistor to supply a first current to the first resistor, the first resistor generating a first voltage thereacross based on the supplied first current for electrically biasing the gate terminal of the first transistor, wherein the first current source includes; a second current source to supply a second current; a second field-effect transistor having a gate terminal, a first conduction terminal connected to the gate terminal thereof, and a second conduction terminal connected to the second current source, the second transistor generating a second voltage at the second conduction terminal thereof based on the second current supplied from the second current source; a second resistor; a third field-effect transistor having a gate terminal, a first conduction terminal connected to the first resistor, and a second conduction terminal connected to the second resistor, the third transistor conducting the first current between the first and second conduction terminals thereof for supply to the first resistor in response to a control signal applied to the gate terminal thereof, the second resistor generating a third voltage at the second conduction terminal of the third transistor conducting the first current; and an operational amplifier having a first input connected to the second conduction terminal of the second transistor, a second input connected to the second conduction terminal of the third transistor, and an output connected to the gate terminal of the third transistor to output the control signal to the gate terminal of the third transistor so as to maintain the third voltage substantially equal to the second voltage. - View Dependent Claims (2, 3, 4)
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5. A constant voltage circuit that converts an input voltage input to a voltage input terminal to generate a constant output voltage output to a voltage output terminal, the circuit comprising:
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an output transistor connected between the voltage input and output terminals to control current flow therethrough according to a regulator control signal applied to a control terminal thereof; a reference voltage generator to generate a reference voltage; a regulator control circuit connected to the reference voltage generator and the voltage output terminal to generate the regulator control signal based on a comparison of the output voltage and the reference voltage for application to the control terminal of the output transistor; and a low-pass filter having a filter input terminal connected to the reference voltage generator and a filter output terminal connected to the control circuit to filter the reference voltage input to the filter input terminal to output a filtered reference voltage to the filter output terminal, the low-pass filter including; a capacitor connected between the filter output terminal and ground; a first field-effect transistor having a gate terminal, a first conduction terminal connected to the filter input terminal, and a second conduction terminal connected to the filter output terminal; a first resistor connected between the gate and first conduction terminals of the first transistor; and a first current source connected to the first resistor to supply a first current to the first resistor, the first resistor generating a first voltage thereacross based on the supplied first current for electrically biasing the gate terminal of the first transistor, wherein the first current source includes; a second current source to supply a second current; a second field-effect transistor having a gate terminal, a first conduction terminal connected to the gate terminal thereof, and a second conduction terminal connected to the second current source, the second transistor generating a second voltage at the second conduction terminal thereof based on the second current supplied from the second current source; a second resistor; a third field-effect transistor having a gate terminal, a first conduction terminal connected to the first resistor, and a second conduction terminal connected to the second resistor, the third transistor conducting a first current between the first and second conduction terminals thereof for supply to the first resistor in response to a control signal applied to the gate terminal thereof, the second resistor generating a third voltage at the second conduction terminal of the third transistor conducting the first current; and an operational amplifier having a first input connected to the second conduction terminal of the second transistor, a second input connected to the second conduction terminal of the third transistor, and an output connected to the gate terminal of the third transistor to output the control signal to the gate terminal of the third transistor so as to maintain the third voltage substantially equal to the second voltage. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13)
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Specification