Digitally programmable delay-locked-loop with adaptive charge pump current for UWB radar system

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Engenharia Electrotécnica e Computadores

The objective of this thesis is to study and design a digitally programmable delay locked loop for a UWB radar sensor in 0.13 m CMOS technology.. Almost all logic systems have a main clock signal in order to provide a common timing reference for all of the components in the system. In certain cases it is necessary to have rising (or falling) edges at precise time instants, different from the ones in the main clock. To create those new timing edges at the appropriate time it is necessary to use delay circuits or delay lines. In the case of the radar system its necessary to generate a clock signal with a variable delay. This delay is relative to the transmit clock signal and is used to determine the target distance. Traditionally, delay lines are realized using a cascade of delay elements and are typically inserted into a delay-locked-loop (DLL) to guaranty that the delay is not affected by process and temperature variations. A DLL works in a similar way to a Phase Locked Loop (PLL). In order to facilitate the operation of the radar system, it is important that the delay value should be digitally programmable. To achieve a digitally programmable delay with a large linearity (independent from matching errors), the architecture of the system is constituted by a digital modulator that controls a 1-bit digital to time converter, whose output will be filtered by the DLL, thus producing the delayed clock signal. The electronic sub-blocks necessary to build this circuit are describe in detail as the proposed architectures. These circuits are implemented using differential clock signals in order to reduce the noise level in the radar system. Design and simulation results of the digitally programmable DLL shows a high output jitter noise for large delays. In order to improve this results a new architecture is proposed. Conventional DLL’s have a predefined charge pump current. The new architecture will make the charge pump current variable. Simulations results will show a improved jitter noise and delay error.