1. Field of the Invention
The present invention relates generally to phase-locked loops, and more specifically to linear phase detectors for high-speed clock and data recovery.
2. Description of the Related art
Data networking has exploded over the last several years and has changed the way people work, get information, and spend leisure time. Local area networks at the office allow for centralized file sharing and archiving. Wireless Application Protocol enabled mobile phones operating over a wide area network allow users access to news updates and stock quotes. The Internet has transformed shopping and has spawned a new recreational activity—web surfing. Many computers are used primarily as interfaces to these networks; thus the expression “the network is the computer” has been coined.
Devices such as network interface cards (NICs), bridges, routers, switches, and hubs move data between users, between users and servers, or between servers. Data moves over a variety of media such as fiber optic or twisted pair cables and the air. These media distort data, making it difficult to be read. Lightwaves traveling in a fiber optic cable reflect at the core-cladding interface and disperse. Twisted pair cables filter higher frequencies. Wireless signals bounce off surfaces in a phenomenon known as multipath, smudging one data bit into the next.
Accordingly, these devices, NICs, bridges, routers, switches, and hubs, receive distorted data and clean it up—or retime it—for use either by the device itself or for retransmission. A useful building block for this is the phase-locked loop (PLL). PLLs accept distorted data and provide a clock signal and retimed (or recovered) data as outputs.
The demands on PLLs have become more stringent with this phenomenal growth in networking. Equipment operating at data rates of 10 gigabits per second is replacing 1 gigabit devices, which recently replaced 100 megabit units. Exacerbating the situation is the competitive nature of the networking business itself. Pricing pressures are enormous but using high-speed specialized processes raises system costs. Thus, there is a need for phase detectors that are capable of operating at these data rates but which can be made using relatively inexpensive process technologies.