A radio frequency (RF) amplifier includes an RF drive adjust circuit adapted to receive an input signal and adjust at least one of the amplitude and phase thereof to output a drive-adjusted input signal; a gain element adapted to amplify the drive-adjusted input signal and to output an amplified signal; and a dynamic impedance transformer adapted to receive the amplified signal, to output an output signal, and to transform a load impedance presented to the gain element by a load in accordance with a desired amplitude of an envelope of the output signal.

An amplifier employs a first and second input stage amplifier, and an output stage amplifier for rail-to-rail operation. The rail-to-rail amplifier is driven by an input signal with a particular common-mode voltage. The first amplifier is active during a first range of common-mode voltages, while the second amplifier is active during a second range. A monitor circuit includes an input differential pair that operates at the same common-mode voltage as the first input differential pair in the first amplifier. The monitor circuit senses when the first amplifier has reached a condition where the amplifier begins to stop working by monitoring a current flowing in the input differential pair. The monitor circuit controls the bias current in the second amplifier's bias circuit such that the second amplifier is enabled when the current in the monitor circuit input differential pair drops down towards zero. The outputs of the first input stage amplifier and the second input stage amplifier are coupled to the input of the output stage amplifier. Since the first and second input stage amplifiers are not on at the same time, the overall gain in the amplifier is reduced. Reducing the gain of the rail-to-rail amplifier results in a reduced size of a compensation capacitor that is coupled across the input and output of the output stage amplifier. The reduction in gain and compensation capacitor results in a lowered amount of chip space and reduced cost for the rail-to-rail amplifier.

A power amplification apparatus includes a carrier amplifier and a peaking amplifier. In the apparatus, a detection and comparison controller detects an envelope signal from an input signal, compares a value of the envelope signal with a threshold, and generates a control signal corresponding to a threshold power. At least one switch performs a switching operation for turning on/off the peaking amplifier according to the control signal.

A composite amplifier includes a main power amplifier (10) and an auxiliary power amplifier (12), which are connected to a load (14) over a Doherty output network (16). Filters (26, 28) are provided for pre-filtering the amplifier input signals in such a way that the signals meeting at the output of the main amplifier have essentially the same frequency dependence.

The invention includes a Doherty power amplifier system having a Doherty power amplifier electrically connected to a Doherty bias circuit. The Doherty amplifier includes a carrier amplifier and peaking amplifier. The Doherty bias circuit includes a current mirror and a first node that works to maintain a constant current in the current mirror as a function of a base voltage at the first node. The base voltage that results in a constant current is passed from a current mirror circuit to the carrier amplifier. The base voltage is at least one of scaled and shifted to produce a second voltage at a second node by employing a scaling/level shifting circuit. The scaling/level shifting circuit includes an input electronically connected to the current mirror circuit. The second voltage is passed through a voltage buffer to the peaking amplifier. An effect of the invention is to generate bias voltages for a Doherty amplifier that dynamically adjust to compensate for manufacturing process and environmental changes.