A novel HBT active transformer balanced Schottky diode mixer

This paper describes a unique HBT active transformer balun which has been monolithically integrated with a GaAs Schottky diode ring quad to construct a double balanced mixer which can operate from DC to >2 GHz. The HBT active balun transformer achieves </spl plusmn/0.5 dB gain balance and </spl plusmn/3/spl deg/ phase balance from DC-5 GHz and provides an in-phase combined IF center-tap output. The HBT actively balanced Schottky mixer achieves positive conversion gain from DC-2 GHz, and excellent LO-IF and LO-RF isolation in excess of 28 dB across the band. Two-tone input IP3's of -6 dBm and -14 dBm were obtained with an LO drive of +15 dBm and +6 dBm, respectively. The unique HBT active transformer balanced Schottky mixer topology can achieve multi-decade balanced performance, whereas, the passive transformer-balun approach is limited to an octave in frequency bandwidth. Furthermore, the HBT active balanced mixer topology is capable of operating from a minimum voltage supply of /spl ap/2 Vbe, which is lower than that achieved with conventional active Gilbert cell-based mixers (3 Vbe), making it potentially attractive for low voltage battery powered applications.