Design of High-Order Type-II Delay-Locked Loops With a Fast-Settling-Zero-Overshoot Step Response and Large Jitter-Rejection Capabilities

In this paper, a design method for high-order delay-lock loops (DLLs) is presented and verified through simulations and physical experiments. The general approach is based on selecting the closed-loop transfer function of the DLL, together with identifying the coefficients of the phase-detector and voltage-controlled delay line, and subsequently, solving for parameters of the loop filter of the DLL. Past DLL design approaches relied more on establishing a desired phase margin requirement than attempting to establish a desired input-output behavior. This limited the realization of DLLs to second order; largely a result of the complicated mathematics that arise. As the method proposed in this paper is based on selecting a desired closed-loop transfer function, the issues of stability or phase margin never come to the forefront. This paper will show how a DLL can be designed to achieve a fast-settling-zero-overshoot step response with large jitter-rejection capabilities. The method is simple and easy to execute. No optimization or iteration is necessary. The method is similar to the methods used to design active-RC filter circuits. A fully programmable experimental prototype involving a custom IC implemented in a 130-nm IBM CMOS process was constructed. DLLs with orders ranging from second to eighth will be investigated.