Abstract: An analog-to-digital converter includes a plurality of comparators that each have an output, two analog data inputs coupled to a differential analog data input, and two reference voltage inputs. The two reference voltage inputs are each coupled to a resistor ladder that contains a plurality of resistors coupled in series. Importantly, the two reference voltage inputs of each comparator are positively biased, meaning that the positive reference voltage input is coupled to a point on the resistor ladder at a relatively higher potential than the negative reference voltage input. The outputs of the comparators are coupled to an encoder that encodes signals at the outputs into a digital signal. By positively biasing the differential reference voltage inputs of the comparators in this manner, the differential gain, dynamic voltage range, and voltage symmetry of the comparators are advantageously improved.

Abstract: According to the preferred embodiment, a phase-locked loop system is provided that overcomes the limitations of the prior art by providing the ability to switch output frequencies without a disruption in the phase lock of the output signal. The system uses a first phase-locked loop coupled with a second phase lock-loop such that their output signals are phase aligned and a switching mechanism for switching between the first phase lock output signal and the second phase lock loop output signal. The system is thus able to switch the frequency of its output without a disruption in the phase-lock of the signal.

Abstract: According to the preferred embodiment of the present invention, a phase-locked loop is provided that overcomes the limitations of the prior art by facilitating fast locking on transition to a different output frequency. The phase-locked loop comprises an oscillator that provides a phase-locked loop output signal at various selected frequencies; a feedback divider; a phase comparator; a memory storage mechanism for storing phase-locked loop control information corresponding to selected output frequencies; and a digital circuit mechanism that receives the control information from the memory storage mechanism on transition to a different output frequency. The control information includes a digital counter value corresponding to the last recorded phase difference of the output signal at the different output frequency. On transition, this information is loaded directly to the digital circuit mechanism, reducing the need and time required for the phase comparator operation to drive the PLL to lock.

Abstract: A variable frequency oscillator circuit includes a ring oscillator circuit, a plurality of adjustment means for adjusting an output frequency of the ring oscillator circuit, at least one of the adjustment means having monotonic behavior, adapted to switch between first adjustment levels at a first rate and at least one of the adjustment means having non-monotonic behavior, adapted to switch between second adjustment levels at a second rate which is less than the first rate, such that the means having monotonic behavior adjusts for monotonicity errors which occur during switching.

Abstract: According to the preferred embodiment, an improved feedforward path is provided that improves the frequency response and reduces the output jitter of a phase-locked loop. Specifically, the frequency response is improved by providing a zero in the frequency response of the phase-locked loop by means of a feedforward path. The feedforward path delivers a feedforward charge to the oscillator of the phase-locked loop. According to the preferred embodiment, the feedforward path reorders the feedforward charge, such that the feedforward charge is stored and distributed equally across all the phase-locked loop output signal sub-cycles.