Analog Test Bus Structure for Wide-Bandwidth High-Frequency Measurements

Analog test buses facilitate the testing of analog components in integrated circuits through dedicated test ports and switches. IEEE 1149.4 is an analog test bus standard that can be calibrated with simple gain correction but cannot calibrate for other sources of error present at higher frequencies, leading to inaccurate measurements. This paper presents a novel analog test bus structure with greater calibration capabilities inspired by the vector network analyzer (VNA) calibration approach that uses multiple known calibration references. These references were integrated within the test bus constructed of voltage and current buffers. IEEE 1149.4 and the proposed test bus were first compared via simulation and then through a discrete component PCB implementation, both aimed at measuring a transimpedance amplifier (TIA). The simulation showed that the proposed test bus exactly measured the amplifier with little error while 1149.4 deviated at higher frequencies. These results were echoed in the physical experiment, with the proposed 4-port deviating slightly from the ideal due to the mismatch inherent in the PCB experiment.