In a general aspect, a circuit can include an input circuit configured to receive an input signal, and an amplifier circuit coupled with the input circuit. The amplifier circuit can include an amplifier, and first and second feedback paths. The first feedback path can be from a positive output to a negative input of the amplifier, and the second feedback path can be from a negative output to a positive input of the first amplifier. The circuit can also include a loop circuit configured to provide a local feedback loop for the first amplifier and configured to control current flow into the positive input of the first amplifier and current flow into the negative input of the first amplifier. The circuit can also include a control circuit that is configured to enable the loop circuit in response to a magnitude of the input signal exceeding a threshold.

This disclosure describes techniques for selecting one of a plurality of modes in which to operate an amplifier. The techniques include configuring input routing circuitry, coupled to first and second inputs of the amplifier, based on the selected one of the plurality of modes; selectively applying a resistance to an output of the amplifier, using feedback routing circuitry, based on the selected one of the plurality of modes; and selectively applying one of a plurality of reference voltages, using reference voltage routing circuitry, coupled to the first and the second inputs of the amplifier, based on the selected one of the plurality of modes.

This disclosure describes techniques for selecting one of a plurality of modes in which to operate an amplifier. The techniques include configuring input routing circuitry, coupled to first and second inputs of the amplifier, based on the selected one of the plurality of modes; selectively applying a resistance to an output of the amplifier, using feedback routing circuitry, based on the selected one of the plurality of modes; and selectively applying one of a plurality of reference voltages, using reference voltage routing circuitry, coupled to the first and the second inputs of the amplifier, based on the selected one of the plurality of modes.

A sensor arrangement comprises a sensor having a first terminal and a second terminal, and an amplifier having an amplifier input for applying an input signal and an amplifier output for providing an amplified input signal, the amplifier input being coupled to the second terminal. The sensor arrangement further comprises a quantizer having a quantizer input and a quantizer output being suitable for providing a multi-level output signal on the basis of the amplified input signal and a feedback circuit having a feedback circuit input coupled to the quantizer output and a feedback circuit output coupled to the first terminal. The feedback circuit comprises a digital-to-analog converter being suitable for generating an analog signal on the basis of the multi-level output signal, the analog signal being the basis of a feedback signal provided at the feedback circuit output. The feedback circuit further comprises a feedback capacitor that is coupled between the feedback circuit output and an output of the digital-to-analog converter, and a voltage source coupled to the feedback circuit output.

An embodiment of an amplifier circuit includes first, second, and third amplifiers. The first and second amplifiers, each of which can be a respective operational amplifier or a respective transconductance amplifier, are configured to amplify a differential input signal with a non-inverting gain. And the third amplifier, which can be an operational amplifier or a transconductance amplifier, is configured to cause the first and second amplifiers to amplify a common-mode input signal with a gain that is less than unity. The third amplifier can also be configured to cause the first and second amplifiers to generate a common-mode output voltage that is substantially independent of the common-mode input voltage. Consequently, in addition to presenting a high input impedance and a low noise factor, such an amplifier circuit has a configurable common-mode output voltage and has a lower common-mode gain (e.g., less than unity, approaching zero) than other non-inverting differential amplifiers.

In optical receivers, cancelling the DC component of the incoming current is a key to increasing the receiver's effectiveness, and therefore increase the channel capacity. Ideally, the receiver includes a DC cancellation circuit for removing the DC component; however, in differential receivers an offset may be created between the output voltage components caused by the various amplifiers. Accordingly, an offset cancellation circuit is required to determine the offset and to modify the DC cancellation circuit accordingly.

This application relates to methods and apparatus for operating MEMS sensors, in particular MEMS capacitive sensors (C.sub.MEMS) such as a microphones. An amplifier apparatus is arranged to amplify an input signal (V.sub.INP) received at a sense node from the MEMS capacitive sensor. An antiphase signal generator generates a second signal (V.sub.INN) which is in antiphase with the input signal (V.sub.INP) and an amplifier arrangement is configured to receive the input signal (V.sub.INP) at a first input and the second signal (V.sub.INN) at a second input and to output corresponding amplified first and second output signals. This converts a single ended input signal effectively into a differential input signal.

The present invention provides a circuit applied to a biopotential acquisition system, wherein the circuit includes an active current source and an amplifier. In the operations of the circuit, the active current source is configured to provide a current to two input terminals of the circuit, wherein the two input terminals of the circuit are coupled to two input electrodes of the biopotential acquisition system; and the amplifier is configured to receive input signals from the two input terminals to generate an output signal.

In optical receivers, cancelling the DC component of the incoming current is a key to increasing the receiver's effectiveness, and therefore increase the channel capacity. Ideally, the receiver includes a DC cancellation circuit for removing the DC component; however, in differential receivers an offset may be created between the output voltage components caused by the various amplifiers. Accordingly, an offset cancellation circuit is required to determine the offset and to modify the DC cancellation circuit accordingly.

A semiconductor device includes a differential amplification circuit that outputs differential output signals Vo1 and Vo2, external output terminals PD1 and PD2 to which one of the differential output signals Vo1 and Vo2 and single end signals Vo3 and Vo4 is selectively supplied, switch units SW1 and SW2 that control a conduction state between the external output terminal PD1 and the feedback line and a conduction state between the external output terminal PD2 and the feedback line, respectively, resistance elements R1 and R2 respectively provided in series with the switch units SW1 and SW2, a CMFB circuit that controls a common mode voltage of the differential amplification circuit according to a difference between an intermediate voltage Vcm of the external output terminals PD1 and PD2 in the feedback line and a reference voltage Vref, and a switch unit SW3 that controls to supply a clamp voltage to the feedback line.