Abstract: A noise limited, video, digital to analog converter having an output transition time control with multiple discrete transition times. This is accomplished by a DAC control circuit in which the slew rate of the current is controlled by providing set current levels in the inverters that drive the DAC output current switches thus limiting the current available for charging and discharging the capacitance on the nodes which control the output signal. Additional control is provided by voltage clamping of these nodes which reduces the input voltage to the analog output and results in a cleaner output waveform.By so regulating and controlling the charging and discharging of these nodes, the variations in operation of the circuit due to the process used to produce the circuit in integrated form as well as temperature and supply voltage are further substantially reduced.

Abstract: According to the preferred embodiment of the present invention pull-up/pull-down circuits are provided that use transistors with different threshold voltages to assure power-up to the correct predetermined state. These circuits have the ability to hold a node up or down while drawing very little DC current. In one embodiment a pull-up/pull-down circuit is provided that powers up to a first state with the pull-up node high and the pull-down node low, and that can be toggled from one state to another. A second embodiment provides a pull-up or pull-down circuit that powers up to the desired state and can be disabled by pulling the pull-up node low or pulling the pull-down node high. The circuits remain disabled until the power to the circuit is cycled.

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.

Abstract: Calibration systems and techniques for analog phase-lock loops (PLLs) providing the capability to dynamically maintain a constant damping factor. Damping factor is calibrated by automatically setting a reference bias current I.sub.r to the PLL's charge pump such that the charge current I.sub.c output therefrom maintains the desired PLL damping characteristic. The technique presented involves selecting a known first frequency F.sub.1 and allowing the PLL circuit to reach steady state, after which a known second frequency F.sub.2 is applied and the PLL circuit is monitored to determine whether steady state at this second frequency F.sub.2 is accomplished within a predetermined target time T.sub.x, which corresponds to the desired damping factor. The determination of whether lock occurs within the target time T.sub.x is then employed to automatically setting the reference current I.sub.r.

Abstract: A switched capacitor, integrated circuit employing at least one non-linear capacitor charged and discharged in response to a reference frequency includes a first conductive device for charging the non-linear capacitor to the supply voltage in response to one polarity of the reference frequency, and a second conductive device for discharging the non-linear capacitor in response to the opposite polarity of the reference frequency to a voltage level opposite that of the voltage source minus the threshold voltage of a third conductive device in the discharge path. Preferably, a pair of non-linear capacitors are employed, each being charged on alternate half cycles of the reference frequency, and the non-linear capacitors are accumulator capacitors. The circuit also include means for rapidly initiating the charging and discharging of said capacitors and for precluding changes in the state of charge or discharge thereof due to parasitic diodes in the circuit.

Abstract: A method of self calibration for a segmented digital-to-analog converter is provided. The segmented digital-to-analog converter converts a digital input code to an analog output consisting of an analog output step and an analog calibration factor. The method comprises the step of determining a trim value for each segment of a segmented DAC. The method continues by storing the trim values in memory. Then, the trim values for a plurality of segments preselected to be enabled by a given digital input signal are summed, thereby producing a digital calibration factor associated with each given digital input signal. Last, storing each digital calibration factor in memory at an address corresponding to the associated digital input signal.

Abstract: A gated current source providing a fast rise time, minimal delay and improved output current tolerance utilizes a non-linear feedback loop between first and second transistors and an appropriate proportioning of resistances coupled to a collector electrode of one of the transistors. The first transistor has its emitter electrode connected to the base electrode of the second transistor and the collector electrode of the second transistor is coupled to the base electrode of the first transistor through a diode. An input pulse is applied to the base electrode of the first transistor through a first resistor and a second resistor having an impedance value relatively low compared with that of the first resistor is connected to the collector electrode of the second transistor. A third transistor, acting as a current sink, has its base electrode connected to the base electrode of the second transistor at which a reference voltage used as a control voltage is produced.