Direct measurement of picosecond propagation delays in individual logic gates by a differential optoelectronic technique

The first direct measurement of single-gate propagation delays in gigabit GaAs digital IC's is described. The technique uses picosecond light pulses to generate short on-chip logic-level-switched pulses and infers single logic gate delays by differential measurement of output waveforms. In the 2-GHz clock-rate D-flip-flop selected for these measurements, single-gate propagation delays of 100 ps were measured in specific NOR gates internal to the flip-flop (FF) with this new measurement technique; the technique is easily extendible to measurement of gate delays of the order of a few picoseconds.