Ultra-wide-bandwidth oscilloscope architectures and circuits

Users of test equipment such as oscilloscopes expect performance and accuracy beyond the level of their device under test in order to insure measurement results correspond to the DUT, not to limitations of the test equipment. This drives the use of bipolar circuitry at the front-end of high-bandwidth oscilloscopes, even if targeted at testing devices in a marketplace dominated by CMOS. Several circuit schematics in 130nm and 90 nm SiGe BiCMOS are presented to demonstrate how bipolar transistors are typically employed to provide broadband DC-coupled amplifiers, samplers, and oscilloscope triggers in the 30 to 70 GHz range. The performance metrics of these circuits depend on many parameters of the underlying process beyond Ft and Fmax, and the design effort and simulation accuracy on many effects beyond the core bipolar device model. Examples drawn from the schematics will illustrate many other facets of optimizing a fabrication process for such uses.