Abstract: A signal generator, such as a fractional-N PLL, has, in its feedback signal path, a divider, a phase circuit, and a fractional accumulator that generates control signals for the divider and the phase circuit. The divider control signal controls the divisor value applied by the divider. In one embodiment, a phase selector selects, based on the phase-circuit control signal, one of a plurality of phase-shifted output signals generated by the PLL's main signal path (e.g., by a multi-phase VCO) and the divider generates the feedback signal for the PLL from the selected signal. In another embodiment, the divider generates a divided signal from one of the phase-shifted output signals, and a phase mixer generates, from the divided signal, a plurality of phase-shifted divided signals and selects, based on the phase-circuit signal, one of the phase-shifted divided signals as the PLL's feedback signal.

Abstract: A driver circuit that has a plurality of output elements that are switched on and off in staggered fashion by signals generated by first and second drive chains of a drive chain configuration. The first drive chain comprises “N” delay elements, each of which produces a time delay equal to tDELAY such that the total time delay produced by the first drive chain is equal to (N×tDELAY). The second drive chain comprises N+1 delay elements, “N” of which produce a time delay equal to tDELAY and one of which produces a time delay equal to ½(tDELAY). Therefore, the total time delay produced by the second drive chain is equal to ((N×tDELAY)+(½tDELAY)). The use of the delay element in the second drive that produces the time delay equal to ½(tDELAY) results in smooth transitions in the transition regions where the driver circuit output signal transitions from high to low and from low to high.

Abstract: A line driver circuit with an output impedance that is set to a value which is based at least in part on the impedance of one or more current sources of the driver circuit. The current source impedance varies depending on the desired output amplitude of the driver circuit. Once the current source impedance is determined, a resistor is selected to be placed in parallel connection with the current source so that the combination of the resistor and the current source impedance will produce a desired output impedance for the driver circuit. Preferably, the driver circuit includes a second current source and second resistor in parallel with each other and a source termination resistor, such that the combination of the current source impedance values and the resistor values produces a desired output impedance for the driver circuit.