Over-30-GHz limiting amplifier IC's with small phase deviation for optical communication systems

For a high-speed limiting amplifier with small phase deviation, a new design technique using a uniplanar passive balun and a narrow-band matching network is proposed. It is revealed that a device with small bias-dependence of parasitic capacitances, such as a high electron mobility transistor (HEMT), and a differential operation using passive baluns enables phase deviations at very high frequency to be reduced. Furthermore, suppressing harmonics can reduce phase deviation in a limiting amplifier, which operates in the highly nonlinear region. To verify these design techniques, two types of limiting amplifier IC's using an InP HEMT and AlGaAs/GaAs BCT technology were designed and fabricated. These IC's feature narrow-band matching circuits for input and output using transmission lines and uniplanar CPW-slot transition balms for differential signals. The devices achieved high frequency operation of over 30 GHz with small phase deviations.