The 0.1 ns Mistake That Delayed an Entire Chip!

6 Aug 2026 • 3 minute read

We’ve all been there. You wake up early, get ready on time, leave home exactly as planned, but suddenly there’s traffic, a long signal, or an unexpected roadblock. By the time you reach your destination, you’re late. Now imagine what your boss is saying, “You left on time, so why are you late?” The answer is simple—real life isn’t ideal

Believe it or not, digital chips face the same problem. Inside a chip, data travels from one flip-flop to another, guided by the clock. Ideally, everything may look perfect. But in reality, tiny manufacturing variations and clock path differences can delay the data just enough to cause timing failures.

That’s why engineers don’t rely on ideal calculations. They calculate the Minimum Clock Time Period using concepts such as is (On-Chip Variation) and CPPR (Common Path Pessimism Removal) to ensure the chip operates reliably in the real world. Let’s understand these concepts as simply as possible.

What Is the Minimum Clock Time Period?

Think of the clock as a school bell. A student (data) must finish one class and reach the next classroom before the next bell rings. If the next bell rings too early, the student is still walking—and that’s exactly what happens in a setup timing violation.

So, the minimum clock period is the smallest period that allows data to safely travel from one flip-flop to the next. The basic formula is extracted during the setup timing analysis. As basic example design is shown below:

But real chips are never ideal. That’s where OCV and CPPR come into the picture.

What Is OCV?

OCV (On-Chip Variation) accounts for real-life manufacturing variations. Some paths become slightly faster, while others become slower due to changes in process, voltage, and temperature. Instead of trusting ideal delays, STA adds margins to make timing analysis more realistic and reliable.

Minimum Clock Time Period with OCV

When OCV is applied, the following mathematical calculations change as shown in the equations below,

Here, we assume:

The launch clock is late
The data path is late
Capture clock is early

This creates the worst-case setup timing condition. The following two 1-minute shorts will explain the calculation in more detail.

Minimum Clock Period Calculation in Static Timing Analysis without OCV?

Minimum Clock Period Calculation in Static Timing Analysis with OCV?

Why Do We Need CPPR?

Sometimes, both launch and capture clocks share the same clock path. OCV incorrectly applies variation to this common path twice, making the timing report more pessimistic than reality. This is where CPPR (Common Path Pessimism Removal) helps. It removes the extra pessimism from the shared clock path, giving a more accurate setup slack.

Minimum Clock Time Period with OCV + CPPRs

The mathematical formula includes the CPPR in the calculation:

Since unnecessary pessimism (Common Path Pessimism) is removed, as shown in the equation above, the required clock period often becomes slightly smaller, and the timing results are closer to what the silicon will actually experience. This 1-minute short will explain things quickly.

Watch the Shorts, practice the formulas, and you’ll find these timing concepts much easier to remember. To learn more about shorts, you can find many such YouTube Shorts/videos under Customer Education – Shorts on various topics. You can subscribe to this channel for more information and daily videos/shorts updates.

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