Integrated circuit signal measurements using an undersampling approach

Integrated circuit (IC) manufacturing processes have been successful in introducing complex high-speed analog and mixed-signal devices. Testing these devices is becoming increasingly difficult. The paper presents a novel method of analyzing analog IC´s using periodic input stimuli and wideband undersampling. In its simplest form, the testing procedure can be implemented in a design by adding an analog switch to sample the response signal at a particular node under test and a buffer to bring the sampled values off-chip. Using a sequential undersampling algorithm to control the switch allows high-frequency signals to be mixed down in frequency and driven off-chip using a low bandwidth buffer. By placing the sampling circuit on-chip, the high-frequency buffering problems associated with a similar system using digital sampling scopes or mixed-signal IC testers can be avoided. The utility of the procedure has been illustrated by measuring the frequency response, slew rate, and transient response characteristics for a unity gain 1.2 μm CMOS opamp