An operational amplifier includes: a first amplifier stage, configured to generate first output voltages according to first input voltages; a second amplifier stage, configured to generate second output voltages according to the first output voltages; a second output stage circuit, configured to replicate an equivalent or a scaled-down version of the first output stage circuit; a first common-mode feedback circuit, configured to keep an output common-mode voltage of the second output stage circuit at a predetermined value; a logic loop circuit configured to, when the operational amplifier operates in a direct current calibration phase, adjust a difference between the first output voltages; a bias circuit, configured to generate a voltage close to a common mode voltage of the first output voltages produced after the operational amplifier is turned on, the voltage serving as a reference voltage of a second common-mode feedback circuit.

The operational amplifier disclosed includes an input stage configured to receive power from a floating supply in a low voltage range that can float according to the common mode voltage at the input. The floating supply facilitates the use of low voltage components that can improve the precision of the operational amplifier by lowering the offset voltage. The input stage includes a first gain stage including field effect transistors and a second gain stage using bipolar transistors. The gain stages can be implemented differently to accommodate different applications and fabrication capabilities.

Reducing a spring softening effect on a capacitive sense element of an electromechanical sensor is presented herein. A system, such as a microphone or an accelerometer, comprises an electromechanical sensor and a voltage-to-voltage converter component. The electromechanical sensor comprises a capacitive sense element and a bias voltage component that applies a bias voltage to a sense electrode of the capacitive sense element. The voltage-to-voltage converter component couples a positive feedback voltage to the sense electrode to maintain a constant charge at the sense electrode to facilitate a reduction of charge flow in the electromechanical sensor representing a spring softening effect on the capacitive sense element. In an example, the spring softening effect on the sense element alters a resonant frequency of the sense element and a gain of the sense element. In another example, the charge flow corresponds to a parasitic capacitance that is electrically coupled to the sense electrode.

A class-D amplifier includes measurement of speaker current via the low-side drive transistors of the amplifier. In one embodiment, a class-D amplifier includes two high-side transistors, two low-side transistors, a first sense resistor, a second sense resistor, and a sigma delta analog to digital converter ( ADC). The two high-side transistors and two low-side transistors are connected as a bridge to drive a bridge tied speaker. The first sense resistor is connected between a first of the low-side transistors and a low-side reference voltage. The second sense resistor is connected between a second of the low-side transistors and the low-side reference voltage. The ADC is coupled to the bridge to measure voltage across the first sense resistor and the second sense resistor.

In some embodiments, a circuit for use in devices involving digital-to-analog conversion of signals includes: a capacitive digital-to-analog converter array and an amplifier. The capacitive digital-to-analog converter includes an input port for receiving a digital input signal and an output port. The amplifier includes capacitive feedback loops that include a first capacitor coupling the output of the amplifier with the input of the amplifier and a second capacitor coupled to the output port of the digital-to-analog converter array at the input of the amplifier. The circuit further includes a set of switches that include a first switch and a second switch coupled with opposed ends of the second capacitor at the input and at the output of the amplifier, respectively.

A monolithically-integrated current-feedback instrumentation amplifier includes two differential pairs of transistors. A drain terminal of transistor is directly connected to a drain terminal of transistor and to a differential voltage amplifier, and is connected to a ground terminal by means of a first sink resistor. A drain terminal of transistor is directly connected to a drain terminal of transistor and to the differential voltage amplifier, and is connected to a ground terminal by means of a second sink resistor. An output terminal of the differential voltage amplifier is connected to a resistive voltage divider. Source terminals of the transistors are directly connected together and to a first bias current source without a degeneration resistor, and source terminals of the transistors are directly connected together and to a second bias current source without a degeneration resistor. A sensing system comprising a piezoresistive N&MEMS sensor and a monolithically-integrated differential readout circuit comprising the amplifier are also provided.

The present invention provides a circuit having a filter with an amplifier circuit for filtering and amplifying an input signal to generate an output signal, wherein a corner frequency of the filter is adjustable to control a settling time of the output signal.

A pseudo-resistor structure, comprises: a first and a second PMOS transistor or PN diode configured as two-terminal devices, wherein the positive terminal of the first PMOS transistor or PN diode is connected to the positive terminal of the second PMOS transistor or PN diode, and wherein the negative terminal of the first PMOS transistor or PN diode is connected to an input (A) of the pseudo-resistor structure and wherein the negative terminal of the second PMOS transistor or PN diode is connected to an output (C) of the pseudo-resistor structure, and a dummy transistor or dummy diode connected to the input (A), wherein the dummy transistor or dummy diode is further connected to a bias voltage for compensating a leakage current through the first and the second PMOS transistors or PN diodes. A closed-loop operational amplifier circuit comprising the pseudo-resistor structure is provided. Also, a bio-potential sensor comprising the closed-loop operational amplifier circuit is provided.

A class-D amplifier includes measurement of speaker current via the low-side drive transistors of the amplifier. In one embodiment, a class-D amplifier includes two high-side transistors, two low-side transistors, a first sense resistor, a second sense resistor, and a sigma delta analog to digital converter ( ADC). The two high-side transistors and two low-side transistors are connected as a bridge to drive a bridge tied speaker. The first sense resistor is connected between a first of the low-side transistors and a low-side reference voltage. The second sense resistor is connected between a second of the low-side transistors and the low-side reference voltage. The ADC is coupled to the bridge to measure voltage across the first sense resistor and the second sense resistor.

A class-D amplifier includes measurement of speaker current via the low-side drive transistors of the amplifier. In one embodiment, a class-D amplifier includes two high-side transistors, two low-side transistors, a first sense resistor, a second sense resistor, and a sigma delta analog to digital converter ( ADC). The two high-side transistors and two low-side transistors are connected as a bridge to drive a bridge tied speaker. The first sense resistor is connected between a first of the low-side transistors and a low-side reference voltage. The second sense resistor is connected between a second of the low-side transistors and the low-side reference voltage. The ADC is coupled to the bridge to measure voltage across the first sense resistor and the second sense resistor.