An overvoltage protection circuit includes an input terminal, an output terminal, a clamp transistor, and a selector circuit. The clamp transistor is configured to control current flow between the input terminal and the output terminal. The clamp transistor includes a first terminal coupled to the input terminal, a second terminal coupled to the output terminal. The selector circuit is configured to control a resistance of the clamp transistor based on a voltage at the input terminal. The selector circuit includes a first terminal coupled to the first terminal of the clamp transistor, a second terminal coupled to the second terminal of the clamp transistor, and a third terminal coupled to a third terminal of the clamp transistor.

A differential amplifying apparatus includes an input matching circuit serving as an input balun to which a signal inputted to an input terminal is input, an output matching circuit serving as an output balun that outputs a signal to an output terminal, first and second amplifiers provided in parallel between the input balun and the output balun and configured to output a differential signal, a diode provided between a reference potential and a path between the input balun and the first amplifier, a second diode provided between a reference potential and a path between the input balun and the second amplifier, and a bias circuit that applies a bias to the first diode and the second diode, in which a cathode of the first diode and a cathode of the second diode are connected to the reference potential side.

An amplifying circuit and a rectifying antenna are provided. The amplifying circuit includes: a first rectifying circuit (20), configured to output a first direct current signal according to an alternating current signal; a second rectifying circuit (30), configured to output a second direct current signal according to the alternating current signal; a differential amplifying circuit (40), configured to receive the first direct current signal and the second direct current signal, amplify a difference between the first direct current signal and the second direct current signal, and output an amplified difference between the first direction current signal and the second direct current, the first direct current signal and the second direct current signal have directions opposite to each other. The amplifying circuit can improve sensitivity of an antenna with relatively low costs.

An isolation amplification circuit having an input stage circuitry and a control circuitry stage interconnected through a galvanic isolation barrier. The input stage circuitry includes a first filter network and a second filter network for supplying first and second output signals in response to the application of first and second electrical input signals. The input stage circuitry includes a first feedback path configured for applying a first feedback signal to a common node of the first filter network to close a first feedback loop around the first filter network and a second feedback path configured for applying a second feedback signal to a common node of the second filter network to close a second feedback loop around the second filter network.

An isolation amplification circuit having an input stage circuitry and a control circuitry stage interconnected through a galvanic isolation barrier. The input stage circuitry includes a first filter network and a second filter network for supplying first and second output signals in response to the application of first and second electrical input signals. The input stage circuitry includes a first feedback path configured for applying a first feedback signal to a common node of the first filter network to close a first feedback loop around the first filter network and a second feedback path configured for applying a second feedback signal to a common node of the second filter network to close a second feedback loop around the second filter network.

An overvoltage protection circuit includes an input terminal, an output terminal, a clamp transistor, and a selector circuit. The clamp transistor is configured to control current flow between the input terminal and the output terminal. The clamp transistor includes a first terminal coupled to the input terminal, a second terminal coupled to the output terminal. The selector circuit is configured to control a resistance of the clamp transistor based on a voltage at the input terminal. The selector circuit includes a first terminal coupled to the first terminal of the clamp transistor, a second terminal coupled to the second terminal of the clamp transistor, and a third terminal coupled to a third terminal of the clamp transistor.

A radio frequency (RF) power limiter includes an input direct current (DC) block, an output DC block, a limiter diode, a RF choke, and a test diode. A first terminal of the limiter diode is coupled to a node between the input DC block and the output DC block, and a second terminal of the limiter diode is coupled to an electrical ground. A first terminal of the RF choke is coupled to the node between the input DC block and the output DC block so that the first terminal of the RF choke is coupled to the first terminal of the limiter diode. A first terminal of the test diode is coupled to the second terminal of the RF choke, and a second terminal of the test diode is coupled to the electrical ground.

Provided are a semiconductor device and a sensor system capable of achieving improvement of noise resistance. Thus, an output circuit 106a in the semiconductor device includes: input terminals 207n, 207p; and an output terminal 208; an output amplifier 201 connecting the input terminals 207n, 207p to the output terminal 208; a feedback element 203 returning the output terminal 208 to the input terminal 207n; a switching transistor 204; and a resistance element 206. A drain of the switching transistor 204 is connected to the input terminal 207n. The resistance element 206 is provided between a back gate of the switching transistor 204 and a power source Vdd and has impedance of a predetermined value or more for suppressing noise of a predetermined frequency generated at the input terminal 207n.

An amplifying circuit and a rectifying antenna are provided. The amplifying circuit includes: a first rectifying circuit (20), configured to output a first direct current signal according to an alternating current signal; a second rectifying circuit (30), configured to output a second direct current signal according to the alternating current signal; a differential amplifying circuit (40), configured to receive the first direct current signal and the second direct current signal, amplify a difference between the first direct current signal and the second direct current signal, and output an amplified difference between the first direction current signal and the second direct current, the first direct current signal and the second direct current signal have directions opposite to each other. The amplifying circuit can improve sensitivity of an antenna with relatively low costs.

An amplification circuit coupled to another circuit by alternating current (AC) coupling includes: an amplifier that amplifies and outputs a signal input from the other circuit or amplifies an input signal and outputs the amplified input signal to the other circuit; a feedback circuit that positively feeds back the signal output from the amplifier to an input of the amplifier; and a low pass filter that attenuates a high frequency component of the signal positively fed back to the input of the amplifier by the feedback circuit, and in which a higher cut-off frequency is set such that a lower cut-off frequency in a combination of the amplification circuit and a high pass filter formed by the AC coupling is lower than a lower cut-off frequency in the high pass filter.