Improved technique for reflection performances in broadband variable gain low noise amplifiers

We propose an improved technique for reflection performances in broadband variable gain low noise amplifiers that does not require preamplifiers and buffer amplifiers. This technique controls the feedback circuit and main amplifier simultaneously to obtain constant input and output impedance values. When the amplifier´s gain changed, the reflection performance remained good. Amplifiers ranging from 750 MHz to 6 GHz fabricated using this technique showed an |S/sub 22/| of less than -10 dB, a |S/sub 11/| of less than -8 dB, and a variable gain range of more than 33 dB @ 2 GHz. Compared with conventional techniques, the |S/sub 22/| showed a 6 dB improvement, the |S/sub 11/| showed a 3 dB improvement, and the variable gain range showed an 8 dB improvement.