Embedded at-speed test probe

The addition of a small analog probe circuit to an ASIC design allows previously unreachable internal signal nodes of the ASIC to be accurately monitored and measured with conventional test equipment. The probe is essentially a high-performance analog multiplexer, that can connect to up to 16 test points inside the core of the ASIC with minimal loading, and buffer these signals accurately to a transmission line driver output connected to a dedicated pad. A 0.65/spl mu/ CMOS implementation of the probe circuit provides a -3 dB bandwidth in excess of 400 MHz.