Pros and cons of H-tree? Advantage of using both buffers and inverters?

o   H-Tree:

o    Advantages:

§  Zero Skew (Ideal): Theoretically capable of achieving zero skew if sinks are perfectly distributed and the tree is perfectly balanced.

§  Symmetric Structure: Predictable and regular routing pattern.

o    Disadvantages:

§  Impractical for Real Designs: Assumes uniform sink distribution, which rarely occurs. Blockages and routing obstacles disrupt the ideal structure.

§  High Insertion Delay: Can lead to long paths from the root to sinks.

§  Resource Intensive: Can consume significant routing area, especially on preferred layers.

§  Large Central Driver: Often requires a very large buffer at the root, consuming significant power and area.

§  Less Flexible: Rigid structure makes it hard to adapt to local density variations or timing requirements.

o   Advantage of Using Both Buffers and Inverters:

o    Flexibility: Provides the CTS tool with more options for delay balancing and phase control.

o    Finer Delay Tuning: Inverters typically have slightly lower delay than equivalent-drive buffers (since a buffer is ~2 inverters). Using inverters allows for finer granularity in delay insertion.

o    Area/Power Optimization: A pair of inverters might consume less area/power than a single equivalent buffer. The tool can choose the most efficient option based on availability and design constraints.