A Wide Range Low Power Low Jitter All Digital DLL for Video Applications

Abstract: Technological advancements in video technology have placed stringent requirements on video analog front ends (AFEs) to deliver high resolutions crisp images while consuming low power to deliver optimal performance. One of the vital parts of an AFE is a delay locked loop (DLL). The DLL is a first order system that aligns  a delayed signal with respect to a reference signal while working in a feedback manner. DLLs find their applications in many electronic devices that deal with clocks in their operation. They are used to improve timing margins and clock delays in microprocessors, memory elements and other such applications. The vital function of a DLL is to delay the input clock (one period delay), by passing it through delay line and aligning the input clock and the delayed clock of the DLL through phase detector. Once this is done multiple phases canbe derived from various stages of the delay line with each providing a stable clock signal that is a delayed version of the input clock. Due to the increasing clock speeds this task of deriving multiple phases has become quite cumbersome. The task may become complicated due to noise generated from switching activity in digital circuits thus resulting in jitter at DLL output. As the design of analog circuits becomes quite exigent especially below the 100 nm mark, the goal hereis to design an all digital DLL to take advantage of the 65 nm process and a simplified design cycle. The aim of this thesis is to implement an all digital delay locked loop with an input frequency range of 60 MHz to 300 MHz with a worst case jitter of 66 ps.The DLL provides 32 uniformly spaced phases between input and output clocks.The DLL operation is divided in to two stages. In the first step the first delayline quantizes input clock period with the help of a binary time to digital converter.Based on this quantization information second delay line introduces actual delay between input and output clocks with 32 intermediate phases in between.The entire process takes up to 9 clock cycles until a lock state is achieved. These 32 phases provide a greater phase resolution enhancing the sync processing characteristics of the video AFE thus improving the one screen display characteristics.