Impact of bipolar transistor parameters on the characteristics of the double-balanced mixer

Impact of integrated bipolar transistor parameters on the double-balanced Gilbert mixer performance is analyzed. The used Gummel-Poon transistor model is based on Horizontal Current Bipolar Transistor (HCBT) integrated technology. Intermodulation distortion and conversion gain are analyzed by harmonic balance simulations. Due to the flexibility of HCBT technology, transistor parameters can be adjusted and their impact on circuit characteristics is examined. Analysis starts at lower level, where distortion of differential amplifier is studied and then it is expanded to the whole mixer where the influence of the each circuit part on distortion is examined. The achieved values of input third-order intercept point (IIP3) of 18 dBm and conversion gain of -3.3 dB for mixer with default transistor parameters are comparable with the commercial mixers. Parameter optimization gives a 4-5 dBm increase of IIP3 with small conversion gain decrease of -0.5 dB. The linearity increase depends on the mixer operating frequency.