In recent years, with the rise of wireless communications technology, such as 5G and Internet of Things, and the continuous development of radio frequency (RF) integrated circuits (ICs), handheld wireless communications devices (mobile devices) are today widely used, and wireless communication has experienced explosive growth.  Currently, with the development of wireless applications such as Global System for Mobile communications (GSM), General Packet Radio Service (GPRS), Wireless Local Area Network (WLAN), and Low Power Bluetooth (BLE), the share of wireless communications equipment in the commercially available mass market has increased significantly.  Consumer demand has turned to low-cost, small size, low power consumption multi-function equipment that includes multi-media features, which promotes the development of the RF IC industry. 
BLE (Bluetooth Low Energy) uses a mixed analog-digital integrated circuit design.  The analog system mainly includes an RF front-end circuit, and the digital back-end circuit mainly includes a digital baseband processor.  A high-frequency power amplifier represents a major portion of a BLE transmitter, its function is to amplify an RF signal to a certain level that can be transmitted by an antenna and received by a specific receiver without being distorted by emitted signals of adjacent channels.  Therefore, in order for the transmitted signal to be successfully received at the destination, the signal must be transmitted with sufficient power.  As a result, the power amplifier dominates the power consumption of the entire transceiver system. 
Conventional power amplifiers are generally classified into different groups: class A, class B, class C, class AB, etc.  Their power-added efficiency (PAE) is relatively low, and the power consumption is relatively high.  The power amplifier structure is usually a relatively simple single-ended or differential structure, and the on-chip bias voltage of the power amplifier is constant.  The performance of the power amplifier is adversely affected by process, temperature, and voltage (PVT) variations. 
FIG.  1 is a block circuit diagram of a high-gain high-efficiency power amplifier circuit as known in the prior art.  The high-gain high-efficiency power amplifier circuit includes a main amplifier circuit 40 and an auxiliary amplifier circuit 46.  Each of the main amplifier circuit and the auxiliary amplifier circuit has multiple amplification stages including a driver stage.  A splitter 54 divides an input signal 52 into two signals 56, 58 to provide to two asymmetrical amplifier paths.  Main amplifier circuit 40 includes a power amplifier 42 that is biased in a class AB and a power amplifier 44 that is biased in the class AB.  Auxiliary amplifier circuit 46 includes a power amplifier biased in a class BC and an amplifier 50 biased in a class C. The power amplifier circuit is referred to as a Doherty amplifier and has a high sensitivity due to the mutual influence of the two amplifier paths.  The power amplifier has a relatively high output back-off power and low efficiency.  Further, because the two power paths are operating at the same time, the power consumption is relatively high. 
FIG.  2 is an RF power amplifier that exhibits high power-added efficiency at high output power.  The power amplifier is based on the fact that the switching transistor is either voltage controlled or current controlled, but not both.  When the voltage (current) amplitude of the power amplifier remains constant, the power transfer is not only maximized, but the power consumption is also reduced, and the excitation level and the final stage are designed for switching operation.  The power amplifier is designed as a relatively simple single-ended structure, and the on-chip bias voltage of the power amplifier is fixed.  The performance of the power amplifier is adversely affected by process, temperature, and voltage (PVT) variations.