Hybrid cascode with an isolated NLDMOS and HBT for X-Band power amplifier applications

A cascode amplifier stage with an isolated NLDMOS and SiGe:C HBT was demonstrated. The main advantages of that circuitry concept are a reduced capacitive portion of the input impedance and a significantly increased power gain in comparison to a single NLDMOS amplifier stage. Additionally a more stable input impedance for different RF input power levels can be obtained. The stable and less capacitive input impedance simplifies the design of integrated impedance matching networks. In a first feasibility study a circuit with a NLDMOS gate width of 90 μm showed a maximum gain of 18 dB and a maximum output power of 10 dBm at 11 GHz. To the authors knowledge the circuit concept of a cascode amplifier containing a HBT and an isolated NLDMOS is presented for the first time.