Power amplifier and low noise amplifier

Power amplifier:

Amplifiers produce from an input signal, an output signal having an increased magnitude (i.e., gain). Essentially, an amplifier produces a constant output power at a higher level. Radio frequency (RF) power amplifiers are commonly used in numerous applications, such as base stations used in wireless communication systems. Modern wireless communication base stations transmit and receive radio frequency (RF) signals through the use of RF power amplifiers. RF power amplifiers are generally designed to provide maximum efficiency at the maximal output power. A typical radio transmitter uses a radio frequency (RF) power amplifier to amplify outbound signals for transmission by an antenna. A radio frequency power amplifier is typically constructed using a printed circuit board, with various components of the radio frequency power amplifier circuit installed on the printed circuit board. The RF amplifier circuit typically includes an input, an active element, a bias circuit element, an output matching network, and an output. RF power amplifiers characterized by a plurality of operating performance characteristics responsive to a quiescent operating point established by a direct current (DC) bias current. The linear power amplifier is driven by a direct current (DC) input voltage, provided for example by a battery in the transmitter, and the efficiency of the power amplifier is given by the ratio of the output power to the DC input power.

Low noise amplifier:

A low noise amplifier (LNA) is utilized in various aspects of wireless communications, including wireless LANs, cellular communications, and satellite communications. A typical receiver for a radio frequency signal (RF signal) comprises a combination of an amplifier and a mixer for signal amplification and frequency conversion. The amplifier, usually a low-noise amplifier (LNA), receives the RF signal, amplifies the RF signal and feeds the amplified RF signal to the mixer which in addition receives a local signal from a local oscillator (LO). A critical building block in a radio receiver is the low noise amplifier (LNA). The LNA amplifies the received signal and boosts its power above the noise level produced by subsequent circuits. An LNA provides a steady gain over a specified frequency bandwidth. One common application is the use of a LNA as the input stage of a receiving circuit, such as in a mobile communication device. In a radio frequency (RF) signal receiving apparatus such as a cellular phone and a base station of a wireless communication system, a received signal has very weak intensity and includes considerable noise mixed therein. As such, the performance of the LNA greatly affects the sensitivity of the radio receiver. The low noise amplifier is capable of decreasing most of the incoming noise and amplifying a desired signal within a certain frequency range to increase the signal to noise ratio (SNR) of the communication system and improve the quality of received signal as well. Depending on signal frequency, an LNA can be implemented as an open loop or closed-loop amplifier and may also have a requirement to match a specific source impedance.