An impedance circuit includes a poly-resistor and a controller. The poly-resistor has a first terminal and a second terminal. The controller generates a first control voltage and a second control voltage. The resistance between the first terminal and the second terminal of the poly-resistor is determined according to the first control voltage and the second control voltage. The second control voltage is different from the first control voltage. The proposed impedance circuit can improve the linearity of the poly-resistor.

In one embodiment a differential amplifier arrangement includes a first input configured to receive a first input signal, a second input configured to receive a second input signal, a first output configured to provide a first output signal, a second output configured to provide a second output signal, a common mode loop configured to regulate an output common mode of the differential amplifier arrangement depending on a difference between a common mode reference signal and an average of the first and the second output signal, and a differential mode loop configured to regulate a differential mode output of the differential amplifier arrangement depending on a difference between a difference between the first and the second input signal and a difference between the first and the second output signal. Therein the difference between the first and the second output signal is substantially constant.

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 (300) is arranged to amplify an input signal (V.sub.INP) received at a sense node (104) from the MEMS capacitive sensor. An antiphase signal generator (201; 304) generates a second signal (V.sub.INN) which is in antiphase with the input signal (V.sub.INP) and an amplifier arrangement (105; 305) 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.

Certain aspects of the present disclosure generally relate to a differential amplifier implemented using a complementary metal-oxide-semiconductor (CMOS) structure. The differential amplifier generally includes a first pair of transistors and a second pair of transistors coupled to the first pair of transistors. The gates of the first pair of transistors and gates of the second pair of transistors may be coupled to respective differential input nodes of the differential amplifier, and drains of the first pair of transistors and drains of the second pair of transistors may be coupled to respective differential output nodes of the differential amplifier. In certain aspects, the differential amplifier may include a biasing transistor having a drain coupled to a source of a transistor of the first pair of transistors and having a gate coupled to a common-mode feedback (CMFB) path of the differential amplifier.

Certain aspects of the present disclosure generally relate to a differential amplifier implemented using a complementary metal-oxide-semiconductor (CMOS) structure. The differential amplifier generally includes a first pair of transistors and a second pair of transistors coupled to the first pair of transistors. The gates of the first pair of transistors and gates of the second pair of transistors may be coupled to respective differential input nodes of the differential amplifier, and drains of the first pair of transistors and drains of the second pair of transistors may be coupled to respective differential output nodes of the differential amplifier. In certain aspects, the differential amplifier may include a biasing transistor having a drain coupled to a source of a transistor of the first pair of transistors and having a gate coupled to a common-mode feedback (CMFB) path of the differential amplifier.

A circuit for amplifying signals from a Micro Electro-Mechanical System (MEMS) capacitive sensor is provided. First and second input nodes receive a sensing signal applied differentially between the input nodes. A first amplifier stage and a second amplifier stage, respectively, produce a differential output signal between first and second output nodes. A common mode signal is detected at the output nodes. A voltage divider having an intermediate tap node is coupled between the first output node and the second output node. A feedback stage is coupled between the intermediate tap node of the voltage divider and the inputs of the first amplifier stage and the second amplifier stage, where the feedback line is sensitive to the common mode signal at the output nodes.

An apparatus, e.g., an optical signal receiver, includes a trans-impedance amplifier (TIA) circuit. The TIA circuit includes a variable gain amplifier (VGA) having a tunable tail current source. The TIA circuit is configured to tune the tail current source to stabilize a DC current to a load resistor of the VGA over an operating gain range of the TIA circuit.

An apparatus includes a preamplifier stage to receive a power supply voltage and generate an output based upon an input. In particular, the preamplifier stage includes a biasing device coupled between the output and a ground node to bias a DC voltage level of the output independently of the power supply voltage. The preamplifier stage also includes a complementary circuit to receive the input and generate the output. The complementary circuit reuses a current through the preamplifier stage to provide an increased transconductance of the preamplifier stage for a given current level.

A semiconductor device is provided that includes an amplification circuit, a downstream circuit, and a clipping circuit. The amplification circuit includes a sampling capacitor, a feedback capacitor, and an operational amplifier circuit. The sampling capacitor holds air input signal on which sampling is performed, as a signal whose reference is a first reference voltage. The signal that is held in the sampling capacitor is transferred to the feedback capacitor. The operational amplifier circuit amplifies the signal that is held in the sampling capacitor, according to a ratio between values of the sampling capacitor and the feedback capacitor, and outputs the amplified signal, as a signal whose reference is a second reference voltage. The clipping circuit limits a voltage of an output signal of the operational amplifier circuit to a predetermined voltage or below.

Disclosed is a differential voltage supplying apparatus configured to supply, to a neural activity recorder, an input signal generated by combining, with a direct current (DC) power supply, a common-mode signal determined from a voltage applied to a detection electrode and a reference electrode connected to the neural activity recorder, and improve a common-mode rejection ratio of the neural activity recorder and generate a DC power supply.