Low-power digitally-controlled variable gain attenuator and LNA with high gain dynamic range for sub-GHz ISM bands

A low-power Digitally-controlled Variable Gain Attenuator and Low Noise Amplifier are implemented in a 40-GHz f_T 0.25-??m BiCMOS process. They cover the sub-GHz ISM bands for automotive applications such as Remote Keyless Entry. The LNA achieves wideband input matching independent of the variable gain, as well as high reverse isolation, thanks to a partial feedback technique. Its variable gain is based on a resistor-chain gain-control technique, leading to fine gain steps and constant output impedance. 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 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. This LNA is preceded by a five coarse steps (about 11?dB each) digitally-programmable attenuator based on a hybrid T and R-2R network. Together with the LNA, more than 50?dB of gain dynamic range is achieved. For high attenuation steps, input IP₃ of more than +18?dBm is reached.