A PLL circuit and method provides an adjustable operating frequency range
by using at least two VCOs. In an embodiment of the present invention,
circuit components of a PLL are adjusted in order to obtain a selected
frequency range. In particular, a gain of a charge pump and resistance of
a filter is adjusted responsive to a control signal. In alternate
embodiments of the present invention, a voltage regulator, including an
operational amplifier, is coupled to the output of the filter and the
respective inputs of two VCOs. An output multiplexer then selects a VCO
output responsive to the control signal. In another embodiment of the
present invention, a multiplexer is coupled to the output of the voltage
regulator to select which VCO receives a buffered voltage. In another
embodiment of the present invention, respective operational amplifiers
that may be enabled or disabled responsive to the control signal are
coupled to a filter output and respective VCO inputs in order to provide
an adjustable frequency range.