Filter circuit and receiving device
AssigneeRenesas Electronics Corporation
InventorsYasuku Katsube, Takeshi Uchitomi, Yutaka Igarashi
Life of this patent
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Abstract
To implement a filter circuit with low noise and a low cutoff frequency in a smaller area, a filter circuit has a first circuit which receives an input signal supplied to an input terminal, amplifies the signal, and outputs the amplified signal to an output terminal, a first differential amplification circuit for receiving the output signal of the first circuit through a first capacitance element, a first resistance element for forming a negative feedback path between the input and output of the first differential amplification circuit, and a second resistance element for forming a negative feedback path between the output of the first differential amplification circuit and the input of the first circuit.
Claims20
A filter circuit comprising:
- a first circuit which receives a signal supplied to an input terminal, amplifies an input signal, and outputs an amplified signal to an output terminal;
- and
- a second circuit which receives the signal output to the output terminal and is feedback-coupled to the input of the first circuit,
- wherein the second circuit includes:
- a first capacitance element;
- a first differential amplification circuit for receiving the signal output to the output terminal through the first capacitance element;
- a first resistance element for forming a negative feedback path between the input and output of the first differential amplification circuit;
- and
- a second resistance element for forming a negative feedback path between the output of the first differential amplification circuit and the input of the first circuit.
A receiving device comprising:
- an antenna unit for receiving a signal;
- a conversion unit for converting the signal received by the antenna unit into a baseband signal;
- a filter circuit for acquiring a signal in a frequency band corresponding to an intended communication system from the baseband signal converted by the conversion unit;
- and
- a control unit for performing control for switching filter characteristics of the filter circuit,
- wherein the filter circuit comprises:
- a first circuit which receives the baseband signal;
- amplifies an input signal, and outputs an amplified signal;
- a second circuit which receives an output signal of the first circuit and is feedback-coupled to the input of the first circuit;
- and
- a switch element for switching connection and disconnection between the first circuit and the second circuit,
- wherein the second circuit includes:
- a first capacitance element;
- a first differential amplification circuit for receiving the output signal of the first circuit through the first capacitance element;
- a first resistance element for forming a negative feedback path between the input and output of the first differential amplification circuit;
- and
- a second resistance element for forming a negative feedback path between the output of the first differential amplification circuit and the input of the first circuit,
- wherein the first circuit includes:
- a second differential amplification circuit for receiving the baseband signal and a signal fed back through the second resistance element;
- a third resistance element for forming a negative feedback path between the input and output of the second differential amplification circuit;
- and
- a second capacitance element placed in parallel to the third resistance element,
- wherein the second capacitance element has a variable capacitance value, and
- wherein the control unit controls the switch element and the capacitance value of the second capacitance element in accordance with the intended communication system.
Dependencies are inferred from the claim text.