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.

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.

The present disclosure relates to circuitry comprising audio amplifier circuitry for receiving an audio signal to be amplified; and first and second output nodes for outputting first and second differential output signals. The circuitry further comprises common mode buffer circuitry configured to receive a common mode voltage and to selectively output the common mode voltage to the first and second output nodes.

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.

A chopper amplifying circuit employing a negative impedance compensation technique, including a differential input end, a first-level chopper switch, a first-level amplifying circuit, a second-level chopper switch, a second-level amplifying circuit, a negative impedance converting circuit, a negative feedback unit, an input capacitor, and a differential output end, is provided. The differential input end is connected to the first-level chopper switch. An output terminal of the first-level chopper switch is connected to the first-level amplifying circuit through the input capacitor. The first-level amplifying circuit is connected to the second-level chopper switch, which is connected to the second-level amplifying circuit. The second-level amplifying circuit is connected to the differential output end, and is also connected to a feedback input end of the first-level amplifying circuit through the negative feedback unit. The negative impedance converting circuit is parallel-connected to a signal input end of the first-level amplifying circuit.

A signal distribution circuit including an equalization circuit, a signal distribution part, an operational amplifying circuit, a feedback circuit, and a time sequence circuit. The equalization circuit is configured to collect an initial broadband signal. The signal distribution part is configured to distribute a first-stage broadband signal resulting from amplitude attenuation process to obtain a plurality of same second-stage broadband signals. The operational amplifying circuit is configured to perform amplification processing on the second-stage broadband signal obtained after distribution to obtain a third-stage broadband signal. The feedback circuit is configured to feedback the third-stage broadband signal to the equalization circuit. The time sequence circuit is configured to adjust an amplification gain of the third-stage broadband signal, and transmit the third-stage broadband signal to an analog to digital converter.

An amplifier arrangement has a first differential stage with a first transistor pair, a second differential stage with a first and a second transistor pair, each pair having a common source connection. The amplifier arrangement further has a first complementary differential stage with a transistor pair having opposite conductivity type, and a second complementary differential stage with a first and a second transistor pair of the complementary conductivity type. The first and the second complementary differential stage are connected symmetrically compared to the first and the second differential stage. The transistors of the second differential stage and the second complementary differential stage are symmetrically connected to form respective first, second, third and fourth current paths. A pair of output terminals is coupled to the first and the fourth current path. Gate terminals of the transistors are coupled to a respective pair of input terminals.

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.

A class-D amplifier includes a loop filter, a pulse-width modulation (PWM) circuit, an output circuit, and a common-mode control circuit. The loop filter receives an input signal of the class-D amplifier to generate a filtered signal. The PWM circuit converts a non-PWM signal into a PWM signal, wherein the non-PWM signal is derived from at least the filtered signal. The output circuit generates an output signal of the class-D amplifier according to the PWM signal. The common-mode control circuit monitors a common-mode level of the output signal to generate a common-mode control signal for PWM common-mode control.

Circuits for low noise amplifiers with interferer reflecting loops are provided. In some embodiments, circuits for a low noise amplifier with an interferer reflecting loop are provided, the circuits comprising: a low noise amplifier (LNA) having an input and an output; a buffer having an input coupled to the output of the LNA and an output; and notch filter having an input coupled to the output of the buffer and an output coupled to the input of the LNA.