| 摘要 |
A phase locked loop system for use with a synchronous dynamic random access memory (SDRAM) or a multi-rate high speed serial transmission buffer is disclosed. The invention includes a phased lock loop having a control voltage for controlling a voltage-controlled oscillator (VCO) that is adjusted, based upon whether the control voltage is within a specific voltage range and whether the VCO frequency is within a specific frequency range. If the control voltage is greater than a voltage maximum and the frequency is not beyond a frequency maximum, the VCO sensitivity is increased. If the control voltage is less than a voltage minimum and the frequency is not below a frequency minimum, the VCO sensitivity is decreased. This ensures that any signal noise or jitter does not have a proportionately large portion of the signal, and therefore minimizes its effect. The VCO sensitivity is increased or decreased by increasing or decreasing the gain of the VCO block respectively to maintain the proper sensitivity to noise while in the defined control voltage range and VCO frequency range.
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