A wide-bandwidth Si/SiGe HBT direct conversion sub-harmonic mixer/downconverter

A wideband sub-harmonic mixer/direct-conversion downconverter is implemented in a Si/SiGe HBT technology, with improved rejection of the local oscillator (LO), high input intercept point, and low current requirements. The circuit utilizes a combination of phase shifters operating at 45/spl deg/ and 90/spl deg/ to achieve better than 33-dB input-referred rejection of the LO. The measured third-order input intercept point (IIP3) was approximately -3 dBm and the second-order input intercept point (IIP2) was roughly 35 dBm, with a measured double sideband (DSB) noise figure of 7.8 dB. A comparison was made between devices of differing germanium concentration in the base, and the devices with higher Ge content exhibited improved noise figure and gain. Each mixer required approximately 2.8 mA from a 3.3 V supply.