Patent ID: 6114920
Filing Date: 2000-09-05
Classification: H03L

Abstract:
An integrated circuit having a self-calibrating oscillator circuit comprising:(a) a voltage-controlled oscillator (VCO) having a plurality of VCO operating curves, wherein the VCO is configured to:(1) receive a VCO control signal that is used to select one of the plurality of VCO operating curves; and(2) generate a VCO output signal whose frequency is a function of the selected VCO operating curve;(b) auto-trim logic configured to:(1) receive a system clock signal having a system clock frequency and a system clock phase, a specified minimum frequency control signal, a specified maximum frequency control signal, and, via a feedback path in the oscillator circuit, the VCO output signal; and(2) generate the VCO control signal;(c) a current DAC (IDAC) configured to receive the VCO control signal; and(d) a summing node configured to generate a current control signal that is applied to the VCO to control the selection of the VCO operating curve, wherein:the IDAC converts the VCO control signal into an IDAC output current;the summing node adds the IDAC output current to a DC current signal to generate the current control signal for the VCO; andduring auto-trim operations, the auto-trim logic compares the system clock frequency to the frequency of the VCO output signal and adjusts accordingly the VCO control signal until the frequency of the VCO output signal is within a specified range defined by the specified minimum frequency control signal and the specified maximum frequency control signal, thereby automatically trimming the VCO to the selected VCO operating curve, such that the frequency of the VCO output signal matches the system clock frequency to within the specified range, but the phase of the VCO output signal is asynchronous with the system clock phase.