Sampling Ocsilloscope On-Chip

Abstract: Signal-integrity degradation from such factors as supply and substrate noise and cross talk between interconnects restricts the performance advances in Very Large Scale Integration (VLSI). To avoid this and to keep the signal-integrity, accurate measurements of the on-chip signal must be performed to get an insight in how the physical phenomenon affects the signals. High-speed digital signals can be taken off chip, through buffers that add delay. Propagating a signal through buffers restores the signal, which can be good if only information is wanted. But if the waveform is of importance, or if an analog signal should be measured the restoration is unwanted. Analog buffers can be used but they are limited to some hundred MHz. Even if the high-speed signal is taken off chip, the bandwidth of on-chip signals is getting very high, making the use of an external oscilloscope impossible for reliable measurement. Therefore other alternatives must be used. In this work, an on-chip measuring circuit is designed, which makes use of the principle of a sampling oscilloscope. Only one sample is taken each period, resulting in an output frequency much lower than the input frequency. A slower signal is easier to take off-chip and it can easily be processed with an ordinary oscilloscope.