Digitally programmable phase-lock loop for high-speed data communications

Abstract

Electronic devices are typically coupled together to operate as systems that require the communication of data between two or more devices. Many of these devices includes a communications circuit, such as receiver, transmitter, or transceiver for this purpose. A typical component in these communication circuits is the phase-lock loop, a circuit that in receiver circuits determines the timing of pulses in a received data signal and in transmitter circuits clocks the data out at a predetermined rate. One problem with phase-lock loops and thus the receiver and transmitter circuits that incorporate them is that they are generally tuned, or tailored, to operate at a certain frequency. This means that one cannot generally use a receiver or transmitter circuit having phase-lock loops tuned for one frequency to communicate at another frequency. The inability to communicate at other frequencies limits the usefulness of not only the receiver and transmitter circuits but also their electronic devices. Accordingly, the present inventors devised a digitally programmable phase-lock loop which operates at a frequency selected from a set of two of more frequencies. One such phase-lock loop includes a charge pump, a loop filter, and a voltage-controlled oscillator, all of which are programmable to control the operating frequency of the phase-lock loop and thus devices, such as receivers, transmitters, and transceivers incorporating it. Moreover, the programmability of these three components enables the exemplary embodiment to maintains a constant damping factor and a constant ratio of input frequency to loop bandwidth for each frequency setting, thereby promoting loop stability and rapid settling at each selected frequency.