LNA Design Using SpectreRF Application Note
LNA Design Using SpectreRF Application Note
Introduction to LNAs- The first stage of a receiver is typically a low-noise amplifier (LNA), whose main function is to provide enough gain to overcome the noise of subsequent stages (for example, in the mixer or IF amplifier). Aside from providing enough gain while adding as little noise as possible, an LNA should accommodate large signals without distortion, offer a large dynamic range, and present good matching to its input and output, which is extremely important if a passive bandselect filter and image-reject filter precedes and succeeds the LNA, since the transfer characteristics of many filters are quite sensitive to the quality of the termination.
LNA Measurements and Design Specifications
Power Consumption and Supply Voltage You must trade off gain, distortion, and noise performance against power dissipation. Total power dissipation for an operating LNA circuit should be within its design budget. Since most LNAs are operated in Class-A mode, power consumption is easily available by multiplying the DC supply voltage by the DC operating point current. Selecting the operating point is a critical stage of LNA design which affects the power consumption, noise performance, IP3, and dynamic range.Three power gain definitions appear in the literature and are commonly used in LNA design.