What are the main timing optimization techniques in digital VLSI design?

Digital VLSI timing optimization employs several key techniques including resizing, buffering, and cloning. Resizing involves selecting appropriately sized gates to achieve optimal delay, while buffering and cloning help manage load by distributing signal driving responsibility. Additionally, designers can redesign fan-in and fan-out trees to better balance signal arrival times, decompose complex gates into simpler ones, and swap commutative pins to optimize critical paths. The most complex but powerful approach is retiming, which repositions registers to balance timing paths and achieve higher throughput while maintaining logical equivalence.