Which statement about setup time and hold time is true?

• A. Setup time refers to data stability after the clock edge
• B. Hold time is the required data stability before the clock edge
• C. Violations of timing have no effect on maximum clock rate
• D. Both setup and hold times constrain the clock period and maximum clock rate

Answer: (D)

The key idea is that timing constraints on data stability around a clock edge determine how fast you can clock a circuit. Setup time is the minimum amount of time the data must be stable before the clock edge, and hold time is the minimum amount of time the data must remain stable after the clock edge. These requirements ensure the flip-flop captures the intended value reliably; if data changes too soon before or after the edge, the register may latch the wrong data or become metastable.

Because the clock period must accommodate not only the data’s travel through the combinational path but also that data being stable before the edge and not changing immediately after the edge, both setup and hold times constrain the minimum clock period. Consequently, they limit the maximum clock rate you can achieve. That’s why the statement that both setup and hold times constrain the clock period and maximum clock rate is true.

The other statements mix up the definitions or dismiss the impact of timing violations: setup time is not stability after the clock edge, hold time is not stability before the clock edge, and violations of these timing constraints do affect the achievable clock rate.