A temperature compensated L-band variable gain amplifier with eight bit digital control

The authors describe a high-performance microwave AGC (automatic gain control) amplifier with an eight bit TTL (transistor-transistor logic)-compatible digital control. The amplifier includes five temperature-compensated gain stages, six RF switches, a 5-bit digital step attenuator, and eight TTL-compatible switch drivers on a single monolithic GaAs integrated circuit operating over an octave of bandwidth in L-band. The most significant performance feature of the amplifier is the ability to maintain both a low noise figure, and a high third-order intercept point throughout most of the gain control range. This is accomplished by embedding three of the stages in switch networks such that the amplifiers can be bypassed with the appropriate control signal. At maximum gain, the noise figure is about 4 dB, and the 1 dB compressed power output is about 16 dBm. The chip is 2.5 by 4.9 mm.<>