Certain aspects of the present disclosure provide methods and apparatus for amplifying an input signal. One example apparatus is a differential amplifier that includes a positive input node, a negative input node, a positive output node, a negative output node, a positive input transistor having a gate coupled to the positive input node and having a drain coupled to the negative output node, a negative input transistor having a gate coupled to the negative input node and having a drain coupled to the positive output node, a first common-gate amplifier having an output coupled to the negative output node, a second common-gate amplifier having an output coupled to the positive output node, a first capacitive element coupled between the negative input node and an input of the first common-gate amplifier, and a second capacitive element coupled between the positive input node and an input of the second common-gate amplifier.

An electronic device may include wireless circuitry with a baseband processor, a transceiver circuit, a front-end module, and an antenna. The front-end module may include amplifier circuitry such as a low noise amplifier for amplifying received radio-frequency signals. The amplifier circuitry is operable in a non-carrier-aggregation mode and a carrier aggregation mode. The amplifier circuitry may include an input transformer that is coupled to multiple amplifier stages such as a common gate amplifier stage, a cascode amplifier stage, and a common source amplifier stage. The common gate amplifier stage may include switches for selectively activating a set of cross-coupled capacitors to help maintain input impedance matching in the non-carrier-aggregation mode and the carrier-aggregation mode. The common source amplifier stage may include additional switches for activating and deactivating the common source amplifier stage to help maintain the gain in the non-carrier-aggregation mode and the carrier-aggregation mode.

Disclosed is a radio frequency (RF) amplifier having channel selectivity. The RF amplifier includes a main path including an amplifier, and a feedforward path including a gain/phase compensator, a high-pass filter, and a mixer.

High-performance radio frequency analog-to-digital converters (RF ADCs) demand high bandwidth, high linearity, and low noise input amplifiers. A Class-AB amplifier, including common-gate transistor devices and common-source transistor devices operating in parallel, offers high bandwidth and high linearity, while offering lower power operation when compared to Class-A amplifiers. The Class-AB amplifier can be followed by a Class-AB unity gain buffer comprising common-source transistor devices to provide additional isolation for the RF ADC from the circuitry preceding the Class-AB amplifier.

Certain aspects of the present disclosure provide methods and apparatus for amplifying an input signal. One example apparatus is a differential amplifier that includes a positive input node, a negative input node, a positive output node, a negative output node, a positive input transistor having a gate coupled to the positive input node and having a drain coupled to the negative output node, a negative input transistor having a gate coupled to the negative input node and having a drain coupled to the positive output node, a first common-gate amplifier having an output coupled to the negative output node, a second common-gate amplifier having an output coupled to the positive output node, a first capacitive element coupled between the negative input node and an input of the first common-gate amplifier, and a second capacitive element coupled between the positive input node and an input of the second common-gate amplifier.

An electronic device may include wireless circuitry with a baseband processor, a transceiver circuit, a front-end module, and an antenna. The front-end module may include amplifier circuitry such as a low noise amplifier for amplifying received radio-frequency signals. The amplifier circuitry is operable in a non-carrier-aggregation mode and a carrier aggregation mode. The amplifier circuitry may include an input transformer that is coupled to multiple amplifier stages such as a common gate amplifier stage, a cascode amplifier stage, and a common source amplifier stage. The common gate amplifier stage may include switches for selectively activating a set of cross-coupled capacitors to help maintain input impedance matching in the non-carrier-aggregation mode and the carrier-aggregation mode. The common source amplifier stage may include additional switches for activating and deactivating the common source amplifier stage to help maintain the gain in the non-carrier-aggregation mode and the carrier-aggregation mode.

High-performance radio frequency analog-to-digital converters (RF ADCs) demand high bandwidth, high linearity, and low noise input amplifiers. A Class-AB amplifier, including common-gate transistor devices and common-source transistor devices operating in parallel, offers high bandwidth and high linearity, while offering lower power operation when compared to Class-A amplifiers. The Class-AB amplifier can be followed by a Class-AB unity gain buffer comprising common-source transistor devices to provide additional isolation for the RF ADC from the circuitry preceding the Class-AB amplifier.

An electronic device may include wireless circuitry with a baseband processor, a transceiver circuit, a front-end module, and an antenna. The front-end module may include amplifier circuitry such as a low noise amplifier for amplifying received radio-frequency signals. The amplifier circuitry is operable in a non-carrier-aggregation mode and a carrier aggregation mode. The amplifier circuitry may include an input transformer that is coupled to multiple amplifier stages such as a common gate amplifier stage, a cascode amplifier stage, and a common source amplifier stage. The common gate amplifier stage may include switches for selectively activating a set of cross-coupled capacitors to help maintain input impedance matching in the non-carrier-aggregation mode and the carrier-aggregation mode. The common source amplifier stage may include additional switches for activating and deactivating the common source amplifier stage to help maintain the gain in the non-carrier-aggregation mode and the carrier-aggregation mode.

A variable gain amplifier includes a first transistor group which is connected to an input terminal and an output terminal, and which amplifies a signal from the input terminal to output the amplified signal to the output terminal; a second transistor group connected to the input terminal; a third transistor group connected to the output terminal; and a controller configured to control the first transistor group, the second transistor group, and the third transistor group so that a total number of the number of transistors to be turned on in the first transistor group and the second transistor group is kept at a constant value, and total numbers of transistors to be turned on in the first transistor group and in the third transistor group are the same.

Disclosed is a radio frequency (RF) amplifier having channel selectivity. The RF amplifier includes a main path including an amplifier, and a feedforward path including a gain/phase compensator, a high-pass filter, and a mixer.