Patent ID: 6392495
Filing Date: 2002-05-21
Classification: H03L,H04L

Abstract:
A frequency tuning circuit comprising:a voltage controlled oscillator (VCO) having a voltage input port and having an output at which is produced a clock signal (Ck) whose frequency is a function of the amplitude of the voltage applied to the voltage input port; a phase detector circuit having an input port adapted to receive data input signals having a data frequency, said phase detector circuit having an output coupled to the voltage input port of the VCO for supplying thereto a voltage causing the clock signal, Ck, to be a function of the frequency of the data input signal; a frequency-only detector circuit with a dead zone (FoDZ) having an input port to which is applied a reference frequency signal, said FoDZ having an output coupled to the voltage input port of the VCO for supplying thereto a voltage for maintaining the frequency at the output of the VCO above a first frequency value, f1, and below a second frequency value, f2, where f2 is greater than f1, and said FoDZ inducing no change to the output clock signal of the VCO when the frequency at the output of the VCO is between f1 and f2; wherein the output of said FoDZ is coupled to the voltage input port of said VCO via a summing circuit, said FoDZ for causing said summing circuit to increase the voltage at the voltage input port of the VCO when the frequency of the signal (Ck) at the output of the VCO tends to go below f1 and for causing said summing circuit to decrease the voltage at the voltage input port when the signal at the output of the VCO tends to go above f2, and wherein the output of said FoDZ causes no change in the voltage at the voltage input port of the VCO when the frequency of the signal at the output of the VCO is between f1 and f2; wherein said summing circuit includes: a) a current source for supplying a current to the voltage input port of the VCO for causing the voltage at the voltage input port to increase; and b) a current sink for drawing current out of the voltage input port of the VCO for causing the voltage at the voltage input port to decrease; and wherein the output of said FoDZ includes a first output for selectively enabling the current source and a second output for selectively enabling the current sink.