An amplifier circuit having improved common mode rejection is provided. This can be achieved by estimating the common mode value of an input signal and using this to adjust a target common mode voltage at the output of the amplifier. This can help avoid the differential gain becoming modified by the common mode voltage.

A differential pair of FETs forms a sensor circuit coupled to a differential current reading circuit that includes a current to voltage converter and an analog to digital converter. An ESD protection circuit interposed between the sensor circuit and the differential current reading circuit adds spurious currents to a differential sensor current output by the sensor circuit. A circuit before the ESD protection circuit switches the sign of the differential sensor current according to a period of complementary phase clock signals which correspond to a sampling interval of the analog to digital converter. A circuit selects signals depending on the value of the period of the phase clock signals to eliminate the spurious currents.

Embodiments of the present disclosure provide a chopper amplifier circuit that includes an operational amplifier, and a notch filter to be operated by a chopping pulse. The notch filter has a first branch that has a first capacitor, and a second branch that has a second capacitor. A chopping delay switch is connected to the first branch and the second branch of the notch filter. A control circuit is to close the chopping delay switch to short-circuit the first branch and the second branch of the notch filter to each other. The control circuit is to detect establishment of feedback signal at the chopper amplifier. The control circuit is to open the chopping delay switch, responsive to detecting establishment of the feedback signal at the chopper amplifier.

Embodiments of the present disclosure provide a chopper amplifier circuit that includes an operational amplifier, and a notch filter to be operated by a chopping pulse. The notch filter has a first branch that has a first capacitor, and a second branch that has a second capacitor. A chopping delay switch is connected to the first branch and the second branch of the notch filter. A control circuit is to close the chopping delay switch to short-circuit the first branch and the second branch of the notch filter to each other. The control circuit is to detect establishment of feedback signal at the chopper amplifier. The control circuit is to open the chopping delay switch, responsive to detecting establishment of the feedback signal at the chopper amplifier.

In a general aspect, a circuit can include an amplifier circuit including a first amplifier, a first feedback path, and a second feedback path. The first feedback path can provide a feedback path from a positive output of the first amplifier to a negative input of the first amplifier. The second feedback path can provide a feedback path from a negative output of the first amplifier to a positive input of the first amplifier. The circuit can also include a loop circuit including a second amplifier. The loop circuit can be configured to provide a local feedback loop for the first amplifier and configured to control current flow into the positive input of the first amplifier and into the negative input of the first amplifier.

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.

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.

In examples of a chopper operational amplifier, a current control circuit comprises a pair of voltage sources, each of which may be varied to generate a voltage signal of a particular value, and multiple inverters, each of which is configured to receive either a clock signal or its complement signal and one of the voltage signals. Based on these inputs, each inverter generates a control signal that is delivered to a corresponding switch in the input stage of the chopper operational amplifier to control the gate voltage of that switch. Based on the difference between the values of the voltage signals, the current control circuit operates to reduce the amplitudes of base currents induced by charge injection at the input terminals of the chopper operational amplifier.

In examples of a chopper operational amplifier, a current control circuit comprises a pair of voltage sources, each of which may be varied to generate a voltage signal of a particular value, and multiple inverters, each of which is configured to receive either a clock signal or its complement signal and one of the voltage signals. Based on these inputs, each inverter generates a control signal that is delivered to a corresponding switch in the input stage of the chopper operational amplifier to control the gate voltage of that switch. Based on the difference between the values of the voltage signals, the current control circuit operates to reduce the amplitudes of base currents induced by charge injection at the input terminals of the chopper operational amplifier.

A semiconductor device includes a magnetic switch provided on a semiconductor substrate. The magnetic switch includes: a Hall element, first and second power supply terminals; a current source driving the Hall element; a switch circuit switching a differential output voltage supplied from two electrodes of the Hall element to a first or second state based on a control signal supplied from a control terminal; an amplifier amplifying a signal from the switch circuit; a reference voltage circuit generating a reference voltage based on a reference common mode voltage and a control signal; a comparator receiving an output signal of the amplifier and the reference voltage; and a latch circuit latching an output voltage of the comparator. The reference voltage of the reference voltage circuit is controlled by switching from a reference value to a voltage with a high or low adjustment value according to the output voltage of the comparator.