Cryogenic Noise Measurement Using an Integrated Broadband SiGe-HBT Shot Noise Source

Accurate noise measurement at cryogenic temperatures using the commonly employed cold-attenuator and variable-temperature-load methods is challenging due to unknown thermal gradients along the cable between the device under test (DUT) and the noise source used for the measurement. This situation becomes worse for on-wafer cryogenic noise measurements due to heating of the DUT induced by the RF and dc wafer probes. Here, we propose a novel on-wafer noise characterization method using a terminated SiGe HBT shot-noise generator as a broadband noise source. The noise source is co-integrated on the same die as the DUT, in this case CMOS and BiCMOS low-noise amplifiers (LNAs) realized in a SiGe BiCMOS technology. We show that, provided the temperature of an on-chip termination resistor is known, the available noise power from the terminated shot-noise source (TSNS) can be directly calculated, obviating the need for deembedding noise contributions associated with unknown thermal gradients. The noise temperature of a DUT can be measured by connecting its input to the TSNS, sweeping the available noise power from the TSNS, and fitting to the resulting power measurement curve. The efficacy of this novel cryogenic noise measurement method has been verified with both cryogenic SiGe HBT and CMOS FET LNAs. Compared with the commonly used cold attenuator method, this method achieved comparable measurement results with reduced overall noise measurement uncertainty.