The Risk of Not Optimizing Clock Power

Clock power is rarely the issue teams expect to limit advanced-node designs. Yet in many chips today, over-driven clock networks quietly consume disproportionate power, reduce thermal headroom, and can constrain achievable frequency. And all while passing traditional sign-off checks and often remaining locked in through tapeout.

Because clocks toggle continuously and span the entire chip, inefficiencies in the clock network compound relentlessly. Once locked into silicon, these costs are paid every cycle, in every product, for the life of the design. Let’s take a closer look at the risk of not optimizing clock power.

Power as a Silent Constraint

Power is a universal constraint for advanced chip designs, increasingly determining whether performance targets, thermal limits, and product differentiation can actually be achieved. While designers spend significant effort optimizing functional logic, the clock network often escapes the same level of scrutiny because it is assumed to be good enough once timing closes, even though power behavior is no longer explicitly examined in a detailed, clock-network-specific way.

Why Clock Power Is Getting Worse

The massive processing required by AI workloads has turbo-charged the problem. There are many dials to turn to optimize power. It turns out the energy consumed by the clock network in most advanced designs is a substantial contributor to the power problem – often without being explicitly identified as such during sign-off, even as logic efficiency improves and overall power budgets tighten. Clock power can quietly erode available budget even when all timing requirements appear to be met.

Clock Networks: A Disproportionate Power Consumer

You can do your own research on the issue. I found some very useful data at numberanalytics.com and embedded.com. A few key statistics are worth repeating:

• In modern chips, clock networks can account for over 50% of the total dynamic power consumption.

Several factors contribute to the power consumption of clock networks:

• Capacitance: The capacitance of the clock network affects how much power is consumed during signal transitions.
• Switching Activity: The frequency at which the clock toggles directly impacts power usage. Higher switching rates lead to increased power consumption.
• Wire Length: Longer wires increase resistance, which can lead to higher power dissipation.

Capacitance, switching activity (or clock speed), and wire length are all familiar problems for advanced chip design. They all drive power consumption in the wrong direction.

It’s also important to note that unlike logic nets, which may toggle infrequently, the clock net has a 100 percent activity factor. Every inefficiency in gate sizing, topology, or loading assumption is therefore paid continuously. Small amounts of excess drive strength can translate into significant power loss when multiplied across deep clock networks and sustained over billions of cycles. This makes clock power uniquely unforgiving: inefficiencies do not average out over time.

Where Traditional Clock Power Analysis Falls Short

Let’s look at some of the basic steps of how the clock tree is implemented:

1. RTL design of clock network, considering items such as net connectivity, number of nodes, required drive strength and estimate wiring load.
2. Synthesize the clock tree.
3. Perform post layout extraction and timing analysis to verify the clock network meets timing specifications. At this stage, the clock network is typically judged complete based on timing closure alone. Once this judgment is made, opportunities to revisit clock power late in the flow are often avoided due to perceived risk.

This is clearly a simplified view of the steps involved, but what happens in step 3 presents a significant opportunity. Tools like static timing analysis can verify overall performance of the clock network to ensure timing is met. But at what cost?

The opportunity here lies in the clock gates that are inserted during synthesis. The choices made by the synthesis tool are influenced by the drive requirements of the elements in each clock tree and an estimate of the loading effects of the wiring. The amount of wiring has become quite large for advanced designs, so small errors in estimates can become big discrepancies in the final layout.

In any clock network, there will be drivers that are too large for the required load, resulting in wasted power. There will also be undersized drivers that will struggle to keep up, also wasting power, though over-sizing is far more common in practice.

A useful analogy here is internal combustion engines in automobiles. If the engine is too small for the car’s weight, it will struggle and waste gasoline. If it’s too powerful for the car’s weight, gas will also be wasted. There is an optimal engine size for a given car configuration from a fuel efficiency point of view. The same is true for clock network drivers.

This combination of scale, electrical complexity, and late-stage risk has made clock power one of the hardest problems to address in practice. The post-layout netlist of the clock network contains all the actual wiring load and clock drivers chosen by the synthesis tool. Some of those drivers will be too small for the required load and some will be too large, based on the difference between the estimate and actual wire loads.

The most reliable way to find these issues is to perform a SPICE-level analysis on the clock network. Historically, this level of electrically accurate analysis has been impractical at full clock-network scale. Until now, this level of analysis was impractical for real designs.

Turning Clock Power Risk into an Addressable Problem

ClockEdge has developed technology that makes electrically accurate clock power analysis practical at full scale – an area that has traditionally been out of reach. Instead of relying on inferred models or averaged assumptions, this approach evaluates clock power behavior directly across complete clock networks under realistic post-layout conditions.

Crucially, this visibility can be applied early in the clock design process, beginning at clock tree synthesis (CTS). By identifying over-driven paths and unnecessary margin at CTS, teams can make informed sizing and topology decisions before inefficiencies are propagated and locked in. This early intervention reduces downstream power waste and minimizes the need for disruptive late-stage changes.

As the design matures, the same electrically grounded analysis continues to provide value, allowing teams to validate clock power assumptions and refine optimization decisions with confidence. By anchoring analysis in actual electrical behavior, clock power optimization becomes a controlled, data-driven exercise rather than a risky late-stage guess – while preserving timing integrity throughout the flow.

Clock power is no longer a secondary concern- it is a growing source of hidden risk in advanced-node designs. When conservative assumptions are embedded early in CTS and left unexamined, unnecessary power consumption can become locked in, quietly constraining performance, thermal headroom, and predictability. The risk of not optimizing clock power is that its impact often goes unnoticed until it’s too late to change.

To Learn More

If clock power is expected to challenge your next design, ClockEdge provides a practical solution to evaluate and optimize clock power using its vPower solution. To see how this technology applies to your clock network before inefficiencies are locked in, request a demo with the ClockEdge team. This is how you can avoid the risk of not optimizing clock power.

Also Read:

Taming Advanced Node Clock Network Challenges: Jitter

Taming Advanced Node Clock Network Challenges: Duty Cycle

How vHelm Delivers an Optimized Clock Network