A current sense amplifier measures a voltage drop in a drive transistor LS to measure the current flowing through the drive transistor LS. The current sense amplifier includes a preamplifier pre-amp, to which a voltage across the drive transistor LS is inputted, and which obtains a positive output and a negative output corresponding to a voltage difference of the inputted voltage across the drive transistor; and a switch sw, which connects the input end of a common mode voltage vcm and the negative output, the common mode voltage vcm serving as the operation reference of the preamplifier pre-amp. A change of the positive output caused by turning on/off the switch sw can be detected.

Provided are a low-phase-shift variable-gain amplifier and a method for processing a radio frequency signal. The low-phase-shift variable-gain amplifier comprises: a differential cascode amplification circuit, which comprises a common-source transistor and a common-gate transistor, wherein a gate stage of the common-source transistor is connected to a first bias voltage via a target resistor, and a gate stage of the common-gate transistor is connected to a second bias voltage; a current-steering structure, wherein one end of the current-steering structure is connected between the common-source transistor and the common-gate transistor, a third current signal outputted by the current-steering structure is used to adjust a gain of the differential cascode amplification circuit; and a phase compensation circuit, wherein one end of the phase compensation circuit is connected between the common-source transistor and the common-gate transistor.

An integrator operating based on a variable current is provided. The integrator includes an operational amplifier, wherein the operational amplifier includes an amplifying stage circuit and a bias circuit. The amplifying stage circuit is configured to provide an amplification gain. The bias circuit is coupled to the amplifying stage circuit and is configured to control a bias condition of the amplifying stage circuit according to the variable current output from a variable current source. In a sampling phase of the integrator, the variable current source switches the variable current to a sampling current value. In an integration phase of the integrator, the variable current source switches the variable current to an integration current value. More particularly, the sampling current value is less than the integration current value.

According to an embodiment, an analog front-end (AFE) circuit includes a power amplifier and a trans-impedance amplifier. At least one of the amplifiers comprises a differential pair of transistors receiving input signals, a folded cascode structure coupled to the differential pair of transistors, and a nulling transistor coupled to the differential pair of transistors. The nulling transistor receives a nulling signal. A tail current of the differential pair of transistors, bias currents in the folded cascode structure, and a nulling current through the nulling transistor are selected such that a sum of half the tail current and a first bias current equals a sum of a second bias current and the nulling current. The configuration reduces flicker noise and offset of the amplifier without significantly increasing current consumption, enabling improved performance in low-power applications such as portable medical devices.