Low-power digitally-controlled variable gain LNA with high isolation for sub-GHz ISM bands

A low-power digitally-controlled variable gain low noise amplifier is implemented in a 40-GHz f_T 0.25 ¿m BiCMOS process. Wideband input matching independent of the variable gain, as well as high reverse isolation are achieved thanks to a partial feedback technique. The variable gain is based on a resistor-chain gain-control technique, leading to fine gain steps and constant output impedance. It covers the sub-GHz ISM bands for automotive applications such as Remote Keyless Entry. This LNA is designed with 15 gain steps of 1 dB. The simulated results for the maximum gain show a Transducer Power Gain of 16.5 dB, a Noise Figure of 2.4 dB and respective input and output IP₃ of -12.1 dBm and +4.5 dBm, while only drawing 1.45 mA from a 2.7 V power supply. The measurement results are slightly degraded because of wire-bonding couplings in the package.