The present disclosure provides an audio circuit capable of inhibiting a current when mute is deactivated. An output terminal of a class D amplifier circuit is connected to an electroacoustic conversion element through a low-pass filter. An output node of a bridge circuit is connected to the output terminal. An integrator integrates and outputs, in a non-mute period in which a mute control signal is negated, a difference between an input signal and a feedback signal corresponding to an output signal generated at the output terminal, and outputs a predetermined bias voltage in a mute period in which the mute control signal is asserted. A PWM comparator compares the output of the integrator with a periodic voltage. A driver switches, in the non-mute period, the bridge circuit according to an output of the PWM comparator, and fixes an output of the bridge circuit in the mute period.

A read-out circuit includes an operational amplifier configured to receive an input voltage through a positive input terminal; a feedback capacitor connected between an output terminal of the operational amplifier and a negative input terminal of the operational amplifier; a sensor charging and discharging circuit configured to charge or discharge a sensor during a first time; a switching circuit connecting the sensor and the operational amplifier during a second time after the sensor is charged or discharged; and a duty control circuit configured to determine a duty ratio of the first time and the second time according to a capacitance of the sensor.

In an embodiment an integration circuit has a first input terminal configured to receive a first input signal, a second input terminal configured to receive a second input signal, an output terminal to provide an output signal as a function of the first and the second input signal, a first and a second amplifier, each being switchably connected between the first or the second input terminal and the output terminal, and a capacitor which is switchably coupled in a feedback loop either of the first or of the second amplifier such that the capacitor and one of the first and the second amplifier form an inverting integrator providing the output signal. Therein the integration circuit is prepared to be operated in a first and a second subphase, wherein in each of first and second subphases one of the first and the second input signals is supplied to the inverting integrator and the respective other one of first and the second input signals is supplied to the respective other one of the first and the second amplifier.

In some examples, an amplifier comprises a first integrator to receive a differential input signal, a second integrator coupled to the first integrator, a third integrator coupled to the second integrator, and a comparator to receive outputs of the second and third integrators, to compare each of the outputs to a reference signal that is below a power supply rail voltage supplied to the amplifier, and to produce an error current based on the comparison. The amplifier also comprises a feedback connection between the comparator and inputs to the second integrator. The feedback connection injects the inputs to the second integrator with a current that is determined at least in part by the error current.

A system may include a plurality of playback paths comprising an open-loop playback path configured to drive an output load and a closed-loop playback path. The closed-loop playback path may include an outer feedback loop comprising one or more integrators, a quantizer, and an output driver for driving the output load, the outer feedback loop having an outer loop feedback gain and an inner feedback loop comprising the one or more integrators and the quantizer and excluding the output driver, wherein the inner feedback loop has a variable inner loop feedback gain which is adjustable to match the outer loop feedback gain.

An embodiment of this disclosure provides an automated payment apparatus. The apparatus includes a photodiode current integrator configured to charge an integration capacitor. The photodiode current integrator includes a first feedback resistor connected along a negative feedback path of an operational amplifier between an output of the operational amplifier and a negative input of the operational amplifier. The photodiode current integrator also includes a second feedback resistor connected along a positive feedback path of the operational amplifier between the output of the operational amplifier and a positive input of the operational amplifier. The photodiode current integrator also includes an integration capacitor connected to the positive input of the operational amplifier and to common circuit ground. The photodiode current integrator also includes a reset switch connected to the positive input of the operational amplifier and to common circuit ground or to additional voltage source. The photodiode current integrator also includes a photodiode connected to the positive input and the negative input of the operational amplifier.

A digital amplifier includes a pulse-width adjustment circuit that adjusts the pulse width of a digital signal, a switching circuit that amplifies the output signal of the pulse-width adjustment circuit, and a feedback signal generator that generates a feedback signal based on the output signal of the switching circuit.

A correlated double sampling integrating circuit is provided. The circuit includes: a sampling and holding module, an energy storage unit and a feedback module. The sampling and holding module is configured to perform sampling and holding for different input signals. The energy storage unit is configured to store charges corresponding to the input signals upon the sampling and holding to generate node signals, and the feedback module is configured to form a negative feedback loop with the energy storage unit to control node signals at an integrating stage to keep consistent with node signals at a resetting stage and prevent output jump of the correlated double sampling integrating circuit. The correlated double sampling integrating circuit reduces noise, and prevents or weakens output jump of the correlated double sampling integrating circuit caused by the increase of the count of integrations.

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.