Described herein is a front-end for a neural recording system that boosts input impedance of the front-end circuit. The front-end includes an amplifier and two choppers. A first input terminal of the first chopper may be coupled to a first output terminal from one or more signal sensors. A first input terminal of the second chopper may be coupled to a second output terminal from the signal sensors. A second input terminal of the first chopper may be coupled to a first output terminal of a feedback subsystem. A second input terminal of the second chopper may be coupled to a second output terminal of the feedback subsystem. The output terminals of each chopper may each be coupled to a different capacitor such that after switching, the voltage of each capacitor remains substantially the same, improving the input impedance of the circuit.

Described herein is a front-end for a neural recording system that boosts input impedance of the front-end circuit. The front-end includes an amplifier and two choppers. A first input terminal of the first chopper may be coupled to a first output terminal from one or more signal sensors. A first input terminal of the second chopper may be coupled to a second output terminal from the signal sensors. A second input terminal of the first chopper may be coupled to a first output terminal of a feedback subsystem. A second input terminal of the second chopper may be coupled to a second output terminal of the feedback subsystem. The output terminals of each chopper may each be coupled to a different capacitor such that after switching, the voltage of each capacitor remains substantially the same, improving the input impedance of the circuit.

Apparatus and associated methods relating to the amplification of an audio signal. In particular, such application is performed by using an audio to pulse train converter configured to convert an analog audio signal to a complementary train of pulses having a duty cycle indicative of the level of the analog audio signal. The audio to pulse train converter can be a class-D amplifier, a sigma-delta amplifier, self-oscillating amplifier, or any other audio amplifier that is configured to provide complementary pulse trains each having a duty cycle that is representative of the input audio signal. The complementary pulse trains are directed to a circlotron that is configured to provide an amplified version of the audio signal at two output nodes. The amplifier circuit may further include one or more low pass filters and/or output reference resistors. Two similar circuits can be configured together to provide stereo audio amplification.

An amplifier may include a first stage configured to receive an input signal at an amplifier input and generate an intermediate signal which is a function of the input signal, and a final output stage configured to generate an output signal which is a function of the intermediate signal at an amplifier output, and a signal feedback network coupled between the amplifier output and input. The final output stage may be switchable among a plurality of modes including at least a first mode in which the final output stage generates the output signal as a modulated output signal which is a function of the intermediate signal, and a second mode in which the final output stage generates the output signal as an unmodulated output signal which is a function of the intermediate signal. Structure of the feedback network and the first stage may remain static when switching between modes.

A sensor circuit is provided with a chopper-stabilized amplifier circuit configured to receive a signal from at least one magnetic sensing element, a sigma-delta modulator (SDM) configured to receive a signal from the chopper-stabilized amplifier circuit, and a feedback circuit configured to reduce ripple in a signal generated by the chopper-stabilized amplifier circuit. The feedback circuit includes a demodulator to demodulate a signal from the SDM in a digital domain by inverting a bit stream of the signal from the SDM according to a frequency chopping rate, a digital integrator configured to integrate an output signal of the demodulator to form an integrated signal, and a digital-to-analog converter (DAC) configured to convert the integrated signal to an analog signal and provide the analog signal to the chopper-stabilized amplifier circuit.

A sensor circuit is provided with a chopper-stabilized amplifier circuit configured to receive a signal from at least one magnetic sensing element, a sigma-delta modulator (SDM) configured to receive a signal from the chopper-stabilized amplifier circuit, and a feedback circuit configured to reduce ripple in a signal generated by the chopper-stabilized amplifier circuit. The feedback circuit includes a demodulator to demodulate a signal from the SDM in a digital domain by inverting a bit stream of the signal from the SDM according to a frequency chopping rate, a digital integrator configured to integrate an output signal of the demodulator to form an integrated signal, and a digital-to-analog converter (DAC) configured to convert the integrated signal to an analog signal and provide the analog signal to the chopper-stabilized amplifier circuit.

An output of a first amplifier is coupled to an input of a first track and hold circuit and an input of a second track and hold circuit. An input of a first summing circuit is also coupled to an output of the first track and hold circuit and an output of the second track and hold circuit. In addition, an input of a second summing circuit is coupled to the output of the first track and hold circuit and the output of the second track and hold circuit. Moreover, an input of a third summing circuit coupled to an output of a modulator and an output of the second summing circuit, and an output of the third summing circuit coupled to an input of the first amplifier.

An output of a first amplifier is coupled to an input of a first track and hold circuit and an input of a second track and hold circuit. An input of a first summing circuit is also coupled to an output of the first track and hold circuit and an output of the second track and hold circuit. In addition, an input of a second summing circuit is coupled to the output of the first track and hold circuit and the output of the second track and hold circuit. Moreover, an input of a third summing circuit coupled to an output of a modulator and an output of the second summing circuit, and an output of the third summing circuit coupled to an input of the first amplifier.

A class-D driver circuit includes a feedback loop including an input integrator stage, a switched modulator, and an output driver stage. A feedback resistor connects an output terminal of the output driver stage with an input node of the input integrator stage to provide a feedback current. The class-D driver circuit also includes a compensation circuit configured to provide a compensation current to an output node of the input integrator stage to relieve a slew rate limitation of the feedback loop, the compensation current having a magnitude based on the magnitude of the feedback current.

An amplifier circuit comprising: a delta-PWM-modulator, a three-level-DAC, a loop-integrator, and a comparator. The delta-PWM-modulator receives a digital-input-signal; and processes the digital-input-signal and a modulator-triangular-signal to generate a delta-pulse-width-modulation-signal. The delta-pulse-width-modulation-signal is representative of the difference between a square-wave-carrier-signal and a digital-pulse-width-modulation of the digital-input-signal. The three-level-DAC receives the delta-pulse-width-modulation-signal from the delta-PWM-modulator and provides a three-level-analog-signal. The loop-integrator comprises: a virtual-ground-node-terminal configured to receive: (i) the three-level-analog-signal from the three-level DAC; and (ii) a feedback-signal from an output stage of the amplifier circuit via a feedback loop; and an integrator-output-terminal configured to provide a loop-integrator-output-signal. The comparator comprises a comparator-input-terminal configured to receive the loop-integrator-output-signal; a comparator-reference-terminal configured to receive a triangular-reference-signal that corresponds to the integral of the square-wave-carrier-signal; and a comparator-output-terminal configured to provide a drive-signal suitable for driving an output-stage of the amplifier circuit.