An operational amplifier comprises: a first amplifier stage 4 comprising a first differential pair of transistors 8, 10 arranged to receive and amplify a differential input signal 18, 20 thereby providing a first differential output signal 22, 24; and a second amplifier stage 6 comprising a second differential pair of transistors 26, 28 arranged to receive and amplify the first differential output signal 22, 24 thereby providing a second differential output signal 38, 40.

A method can be used to measure a load driven by a switching amplifier having a differential input, an LC output demodulator filter and a feedback network between the amplifier output and the differential input. The amplifier is AC driven in a differential and in a common mode by applying a common. The feedback network provides feedback towards the differential input from downstream the LC demodulator filter by computing the impedance of the load as a function of the differential mode output current and the common mode output current. The feedback network provides feedback towards the differential input from upstream the LC demodulator filter by measuring the impedance value of the inductor of the LC demodulator filter, and computing the impedance of the load as a function of the differential mode output current, the common mode output current and the impedance value of the inductor of the LC demodulator filter.

In one implementation, a circuit can include a reference pin and an operational amplifier that can include an output pin, an inverting input pin and a non-inverting input pin. The inverting input pin can be electrically coupled to the output pin via a first impedance and to the reference pin via a second impedance. The non-inverting input pin can be electrically coupled to the reference pin via a third impedance and can be configured to receive a detection signal. The reference pin can be configured to receive a detection reference signal associated with the detection signal.

Provided is a semiconductor integrated circuit including a pad Pd1 provided on one end side of a resistive element R1 externally provided, a pad Pd5 provided on a different end side of the resistive element R1; an operation amplifier A1, a signal line L11 wired between an output terminal of the operation amplifier A1 and the pad Pd1, a signal line L21 wired between an inverting input terminal of the operation amplifier A1 and the pad Pd5, a ESD protection element r11 provided to the signal line L11, and a signal line L31, through which a voltage signal of the pad Pd1 is transmitted. The signal line L31 is connected to the pad Pd1.

Equalizer circuitry includes a differential target voltage input, an equalizer output, a first operational amplifier, and a second operational amplifier. The differential target voltage input includes a target voltage input node and an inverted target voltage input node. The first operational amplifier and the second operational amplifier are coupled in series between the differential target voltage input and the equalizer output. The first operational amplifier is configured to receive a target voltage signal and provide an intermediate signal based on the target voltage input signal. The second operational amplifier is configured to receive the intermediate signal and an inverted target voltage signal and provide an output signal to the equalizer output. The first operational amplifier and the second operational amplifier are interconnected with one or more passive components such that a transfer function between the differential target voltage input and the equalizer output is a second-order complex-zero function.

In at least one embodiment, a differential amplifier including first and second current transfer systems, a current difference producing system, and a feedback network circuit is provided. The first current transfer system generates a first differential current signal. The second current transfer system generates a second differential current signal. The current difference producing system receives the first differential current signal and the second differential current signal and generates a voltage difference signal that is indicative of a difference between a first current signal and a second current signal. The feedback network circuit converts the voltage difference signal into at least two converted current signals and provides the at least two converted current signals to one of the first and second current transfer systems or the current difference producing system to minimize the difference between the first current signal and the second current signal.

The present invention generally relates to a structure and method of audio amplifier by dynamic impedance adjustment, including a power amplifying unit, a loud-speaker, a current sensing unit and a subtraction unit. The power amplifying unit has a fixed closed loop gain, with an input side and an output side; the loud-speaker is electrically connected to the output side of the power amplifying unit; the current sensing unit senses the output current of the power amplifying unit, and the sensed output current is converted into a current control voltage signal; the subtraction unit inputs the audio voltage signal and the feedback current control voltage signal, and outputs the difference of the audio voltage signal minus the current control voltage signal, and inputs it to the input side of the power amplifying unit. The output sound quality of the loud-speaker is improved by dynamic impedance adjustment.

An integrated cinema amplifier comprises a power supply stage that distributes power over a plurality of channels for rendering immersive audio content in a surround sound listening environment. The amplifier automatically detects maximum and net power availability and requirements based on audio content by decoding audio metadata and dynamically adjusts gains to each channel or sets of channels based on content and operational/environmental conditions. A power supply stage provides power to drive a plurality of channels corresponding to speaker feeds to a plurality of speakers. The amplifier has a front panel having an LED array with each LED associated with a respective channel or group of channels of the multi-channel amplifier, and a control unit configured to light the LEDs according to display patterns based on operating status or error conditions of the amplifier.

A precharge circuit comprises a gain amplifier, a comparator, a reservoir capacitor, a switch, a current source, and a switching network. The gain amplifier has a gain G1 and receives an input voltage Vrefp. The gain amplifier outputs an amplified voltage G1Vrefp to the comparator, which compares G1Vrefp to a voltage across the reservoir capacitor. The comparator outputs a control signal for the switch based on the comparison. The switch couples the current source to the reservoir capacitor. The current from the current source charges the reservoir capacitor. The switching network couples the reservoir capacitor to an output of the precharge circuit during a first operating mode and provides the input voltage Vrefp to the output during a second operating mode.

According to an aspect of the invention, an electronic lock is conceived, being adapted to harvest energy from a radio frequency (RF) connection established between a mobile device and said electronic lock, further being adapted to use the harvested energy for processing an authorization token received via said RF connection from the mobile device, and further being adapted to use the harvested energy for controlling an unlocking switch in dependence on a result of said processing.