Variable gain low noise amplifier

摘要

A commonly used variable gain low noise amplifier (lna) works as a simple cascaded differential pair. In this invention the second cascade output is crossed over to the output node of opposite polarity rather than connected to the supply. The cascade voltages cancel each other out and this can be used to further control the amplifier performance. An additional variable tail current source may be used to add dc tail current for lower gain modes. This increases the IP1dB by decreasing the modulation depth in the input transistor pairs. Attenuation and gain ranging from -10dB to +20dB can be achieved.