Design of a Fixed IF Down-Conversion Double-Balanced Mixer for UHF Band Applications.

Area of Science:

• Electrical Engineering
• Radio Frequency (RF) Engineering
• Semiconductor Devices

Background:

• High dynamic range mixers are crucial for modern wireless communication systems.
• Existing mixer designs often face limitations in linearity, noise performance, and isolation.
• SiGe HBT technology offers advantages for high-frequency analog circuit design.

Purpose of the Study:

• To present a novel SiGe HBT-based double-balanced down-conversion differential mixer.
• To achieve high dynamic range and superior performance metrics for demanding applications.
• To validate the design through comprehensive measurements across a wide operating band.

Main Methods:

• The mixer incorporates a single-ended to differential-balanced RF stage with dual feedback linearization.
• Key components include a local oscillator (LO) balun, LO mixing cores, and a fixed intermediate frequency (IF)-tuned circuit.
• Fabrication and testing were performed using SiGe Heterojunction Bipolar Transistor (HBT) technology.

Main Results:

• Achieved a Single Sideband (SSB) noise figure of approximately 7 dB ± 0.4 dB.
• Obtained a conversion gain of approximately 12 dB ± 1 dB across the 0.5 GHz to 1.8 GHz band.
• Demonstrated excellent isolation (>35 dB RF-to-IF, >50 dB LO leakage) and return loss (>8 dB RF/LO, >18 dB IF).

Conclusions:

• The developed SiGe HBT mixer exhibits high dynamic range and excellent linearity, evidenced by a third-order intercept point of +4.7 dBm.
• The mixer's performance metrics meet the stringent requirements for cellular base stations, SATCOM, and military radar.
• This design represents a significant advancement in mixer technology for high-performance RF applications.