Abstract: A circuit for providing precise delays includes a phase-locked loop driven by a reference frequency source such as a crystal oscillator and including a variable delay circuit. The output of the oscillator is applied to the delay circuit and the non-delayed and delayed signals are compared in a phase comparator. An error signal representative of phase error is developed and applied to vary the amount of delay until the phase error is eliminated. A precise delay referenced to the oscillator frequency is therefore achieved.

Abstract: An integrated circuit chip is fabricated with an operational active device and a nearly-identical, exemplary active device. The exemplary device is connected in series with a current reference element so that current flow through the reference element will be substantially duplicated in the exemplary device. A difference amplifier senses the output voltage of the exemplary device; compares it to a provided reference voltage; and generates a gate biasing level at the gate of the exemplary device to force the output voltage of the exemplary device substantially equal to the reference voltage. The biasing level at the gate of the exemplary device is duplicated at the gate of the operational device thereby creating a condition wherein the output current of the operational device will be a substantially precise replica of the current flow through the reference element when the reference voltage is duplicated across the output of the operational device.

Abstract: A voltage controlled oscillator includes an inverting amplifier connected to a resonant feedback network and a comparator for comparing the input to the inverting amplifier to a reference voltage which is equal to the threshold voltage of the inverting amplifier. As a result, the oscillator provides a square wave output having a precise one-to-one duty cycle. In addition, circuitry is included for causing the oscillator to start up at a steady state value and predetermined phase.

Abstract: The present invention provides a circuit which facilitates fast and reliable start-up of an oscillator crystal without the amplification of undesirable frequencies of noise. A crystal is provided which is connected in parallel to an amplifying inverter having an input and an output. Grounded capacitors are connected respectively to the input and output of the inverter for stability. A first high resistance feedback path and a second low resistance feedback path are provided between the output of the inverter and the input of the inverter. A switch is also provided for selectively engaging or disengaging the low resistance feedback path with the inverter at preselected points in time. During operation of the circuit in the preferred manner, the switch engages the low resistance feedback path with the inverter to allow maximum charge build-up at the stabilizing capacitors upon turn-on of a supply voltage, thus quickly generating a large input voltage at the inverter.

Abstract: A voltage controlled oscillator includes automatic adjust circuitry to achieve and maintain desired operating characteristics such that for a predetermined output frequency the oscillator will have a predetermined input voltage. The oscillator may advantageously be incorporated into a phase locked loop circuit. The phase locked loop will lock onto the frequency of an input signal. Automatic adjust circuitry monitors the input to the voltage controlled oscillator in the phase locked loop and varies the amount of a bias voltage applied to the oscillator so that the input voltage to the oscillator will change until it reaches the desired level. The provision of the automatic adjust circuitry enables the desired operating characteristics of the oscillator to be maintained in spite of long term changes in the circuit operation.