An amplifier is utilized in various applications of remote sensing and communication equipment. Applications of the amplifier include radar, ultrasound, wireless communication and even speech analysis. These applications use the amplifier to enhance dynamic performance. An amplifier is categorized as low noise amplifier (LNA), variable gain amplifier (VGA) and programmable gain amplifier (PGA). Each of these amplifiers is used to sense and amplify low level signals.
The low noise amplifiers (LNAs) are used in receivers to amplify radio frequency (RF) signals received by a receive antenna. LNAs which are required to present a high input impedance have a V2I (voltage to current) architecture followed by an I2V (current to voltage) architecture. A gain programmability of the LNA is incorporated into the V2I architecture so as to maintain similar signal current level and signal to noise ratio (SNR) across different values of the gain.
Depending on signal frequency, an LNA can be implemented as an open loop or closed-loop amplifier. LNA input and output connections can be single-ended or differential. When the LNA is used both in single-ended and differential modes, a set of switches used in the V2I architecture invariably see a large voltage swing which degrades linearity of the LNA.