An L-band gain and bandwidth tunable low-noise differential amplifier using varactor-tuned bias circuits and active loads

An L-band gain and bandwidth tunable low-noise differential amplifier has been developed for the next generation reconfigurable wireless radios. It employs a varactor-tuned base bias circuit for tuning a lower band-edge frequency of the amplifier, a varactor-tuned collector bias circuit for tuning a higher band-edge frequency of the amplifier, an active load for a fine tuning of gain, and a cascode HBT for a coarse tuning of gain. With the use of the varactor-tuned bias circuits, the lower band-edge frequency can be varied from 0.3 to 0.8 GHz for a fixed higher band-edge frequency of 1.7 GHz. On the other hand, the higher band-edge frequency can be varied from 0.7 to 1.7 GHz for a fixed lower band-edge frequency of 0.3 GHz. With the use of an active load and a cascode HBT, a fine tuning range of gain up to 2.8 dB over 1.3 to 1.5 GHz and a coarse tuning range of gain up to 23 dB across 0.7 to 1.5 GHz have been successively achieved. Since the frequency response including lower and higher band-edge frequencies as well as gain level can be tuned independently, the amplifier is considered to greatly contribute to realizing the next generation reconfigurable wireless transceivers.