An amplifier that amplifies a differential signal includes first and second input terminals for receiving two input signals; first and second diodes each including an anode and a cathode, the anodes being electrically connected to the first and second input terminals; first and second bias current sources being respectively electrically connected to the cathodes of the first and second diodes; an operational amplifier connected to the cathode of the first diode and the cathode of the second diode and configured to amplify a differential signal between signals generated at the cathodes of the first and second diodes; a capacitive element being electrically connected between an input and an output of the operational amplifier; and a differential amplifier provided between the operational amplifier and the first and second input terminals and configured to amplify the two input signals. The first and second bias current sources include a current mirror circuit.

A differential pair gain stage is disclosed. In one embodiment, the gain stage includes a differential pair of depletion-mode transistors, including a first and a second n-type transistor. In certain embodiments of the invention, the depletion mode transistor may be GaN (gallium nitride) field effect transistors. The gain stage includes an active load including one or more depletion mode transistors electrically coupled to at least one of the drains of depletion mode transistors of the differential pair. The active load may include a source follower for maintaining the AC voltages at the drains of the differential pair at a constant value and may further include a casocde stage for setting a fixed drain source voltage across the output transistors to increase the output impedance and gain of the stage.

A variable gain amplifier includes an input transistor, an auxiliary transistor, an active inductor and an input current replica circuit. The input transistor is arranged for receiving an input signal to generate an output signal at an output terminal. The auxiliary transistor is coupled to the output terminal of the input transistor, wherein a current of the output terminal flows into the input transistor and the auxiliary transistor. The active inductor is coupled to the output terminal of the input transistor. The input current replica circuit is coupled to the output terminal of the input transistor, wherein a current flowing through a portion of the input current replica circuit is equal to the current flowing through the input transistor, and both a current of the active inductor and the current of the portion of the input current replica circuit flow into the output terminal of the input transistor.

A method for improving the linearity of a radio frequency power amplifier, a compensation circuit (307) for implementing the method, and a communications terminal with the compensation circuit (307). In the method, a compensation circuit (307) is connected between a base (a3) and a collector (b3) of a transistor of a common emitter amplifier (306), in order to neutralize the impact of a variation in capacitance between the base (a3) and the collector (b3) of the transistor (306) according to a radio frequency signal. No additional direct-current power consumption is needed, and degradation in performance of other radio frequency power amplifiers can be avoided. The corresponding compensation circuit (307) can be easily integrated with a main amplification circuit, without affecting other performance of the main amplification circuit, and provides high adjustability.

A signal transfer circuit includes a transmission circuit, a conversion circuit and a sensing output circuit. The transmission circuit outputs a driving signal to a signal line. The conversion circuit receives an input signal that is a single-ended signal transferred through the signal line and converts the input signal to a differential signal including a first output amplified signal and a second output amplified signal. The first output amplified signal swings downwardly from a first output DC level and the second output amplified signal swings upwardly from a second output DC level that is lower than the first output DC level. The sensing output circuit generates an output signal based on the differential signal. The number of the signal lines is reduced without decrease in performance of signal transfer, and sizes of the signal transfer circuit and the device including the signal transfer circuit are reduced.

An amplifier that amplifies a differential signal includes first and second input terminals for receiving two input signals; first and second diodes each including anode and cathode, the anodes being electrically connected to the first and second input terminals; first and second bias current sources being respectively electrically connected to the cathodes of the first and second diodes; an operational amplifier connected to the cathode of the first diode and the cathode of the second diode and configured to amplify a differential signal between signals generated at the cathodes of the first and second diodes; a capacitive element being electrically connected between an input and an output of the operational amplifier; and a differential amplifier provided between the operational amplifier and the first and second input terminals and configured to amplify the two input signals. The first and second bias current sources include a current mirror circuit.

Provided is a preamplifying circuit, including a first amplifier and a second amplifier sequentially connected in series, wherein an output end of the second amplifier is connected to a circuit output end, and an input end of the first amplifier is connected to a circuit input end. The preamplifying circuit further includes a positive feedback branch including a diode group and a third amplifier, wherein one end of the diode group is connected to the input end of the first amplifier. The positive feedback circuit can positively feed part of signals back to the other end of the diode group, so that voltage drops at two ends of the diode group can be reduced, and harmonic distortion caused by nonlinearity of the diode group is reduced. Thus, the sound quality detected by a microphone sensor is improved.

A class D amplifier output stage including an input for receiving an input signal, an output for providing an output signal to a load, serially coupled upper and lower switching devices configured to provide an output signal to the output, a driver circuit configured to receive the input signal, and to derive therefrom first and second drive signals for driving the upper and lower switching devices alternately from a conducting state into a non-conducting state and vice versa, such that the conducting state periods of the upper switching device with respect to those of the lower switching device are mutually exclusive and separated by dead time intervals during which both upper and lower output transistors are non-conducting. To reduce distortion and more particularly, total harmonic distortion (THD), the amplifier output stage includes a substantially linear circuit configured to provide a bidirectional current sink for residual currents from the load occurring during at least part of each dead time interval.

A variable gain amplifier includes an input transistor, an auxiliary transistor, an active inductor and an input current replica circuit. The input transistor is arranged for receiving an input signal to generate an output signal at an output terminal. The auxiliary transistor is coupled to the output terminal of the input transistor, wherein a current of the output terminal flows into the input transistor and the auxiliary transistor. The active inductor is coupled to the output terminal of the input transistor. The input current replica circuit is coupled to the output terminal of the input transistor, wherein a current flowing through a portion of the input current replica circuit is equal to the current flowing through the input transistor, and both a current of the active inductor and the current of the portion of the input current replica circuit flow into the output terminal of the input transistor.

An apparatus for performing capacitor amplification in an electronic device may include a first resistor and a second resistor that are connected in series and coupled between a set of input terminals of a receiver in the electronic device, a common mode capacitor having a first terminal coupled to a common mode terminal and having a second terminal, and an alternating current (AC)-coupled amplifier that is coupled between the common mode terminal and the second terminal of the common mode capacitor. The first resistor and the second resistor may be arranged for obtaining a common mode voltage at the common mode terminal between the first resistor and the second resistor. In addition, the common mode capacitor may be arranged for reducing a common mode return loss. Additionally, the AC-coupled amplifier may be arranged for performing capacitor amplification for the common mode capacitor.