TrueDigital DLL

All-Digital DLLs Save Time and Reduce Risk

TrueDigital DLLs (delay-locked loops) are used to
advance or delay clock or data signals in a variety of applications.

They operate in a similar function to PLLs but are used for different applications. Both operate with a feedback loop that locks the phase of an output signal train to a reference signal to ensure the two are precisely timed. This is particularly important in digital systems that run at high data rates with fast clock/signal edges. They differ only in how they synchronize system and signal clocks.

The primary application for a DLL is deskewing. Propagation delay accumulates when a clocking signal travels on interconnects, traverses buffers and gates, or is somehow delayed throughout the system. DLLs can remove skew and synchronize the phase of a system clock before sending it to multiple components. This ensures the components receive clock pulses that are in-phase, ensuring they stay synchronized.

TrueDigital DLLs can be implemented to address clock-domain alignment. They can be configured with different insertion delays to simultaneously reduce clock uncertainty and align two independent clock trees. Aligning clocks at interfaces simplifies communication between flops across hierarchical blocks. Lower clock uncertainty results in significant reductions in power and leads to faster timing closure by eliminating hold violations. It also enables faster clock rates and SoC throughput by reducing setup time.

Movellus features a hierarchical DLL architecture that uses a master lane to calibrate core DLL characteristics thus minimizing circuitry in downstream DLLs. This is useful in chip-to-chip IO links and parallel hard disk read/write heads that require alignment of multiple bits with varying arrival times.

Fully synthesizable, TrueDigital DLLs fit seamlessly with existing digital workflows and methodologies to significantly reduce development time. They consume a minimum number of routing layers, employ standard DFT features, and allow easy migration to new processes or PDKs. TrueDigital DLLs are silicon-proven across foundries including TSMC, GF, UMC, Fujitsu, and are commonly used by customers in volume production. They can also support implementation for non-standard process nodes in a fraction of the time of analog DLLs.