In summary, variable gain amps are required in radio transmitters and receivers for a number of performance optimization reasons. The standard architecture is a combination of a variable attenuator and a fixed gain amp. Depending on whether the signal chain is RX or Tx, the line-up will be either attenuator-amp for the receiver or amp-attenuator for the transmitter. By using a combination of a variable attenuator with a variable gain amplifier, the noise figure vs. gain of the overall amplifier can be made to be nearly constant over a significant part of the gain range.