Phase noise minimized phase/frequency-locked voltage-controlled oscillator circuit

Abstract

A phase noise minimization circuit is disclosed, to be used in a voltage-controlled oscillator (VCO) circuit embedded in a feedback system. The phase noise minimization circuit includes a noise power meter to analyze the control voltage fed into the VCO by the feedback system and determine its voltage noise power. Since the VCO is controlled by the feedback system, the control voltage noise power is also an indication of the VCO phase noise power for frequencies offset within the bandwidth of the feedback system. The VCO has several parameters that can be adjusted to affect its phase noise. A minimization algorithm generates the optimum set of parameters that minimize the control voltage noise power (and thus the VCO phase noise power), and sends them to the oscillator. The phase noise minimization circuit may be used in a variety of applications, particularly in phase-locked loop and frequency-locked loop VCOs.

1 . A phase noise minimization circuit to operate in a feedback system, the circuit comprising:
 a calibration circuit, comprising:
 a noise power meter to receive a control voltage fed into an oscillator, the oscillator, part of the feedback system, to generate an output frequency, wherein the noise power meter analyzes voltage noise present on the control voltage that corresponds to a phase noise power of the oscillator within a bandwidth of the feedback system, the analysis resulting in a control voltage noise power; and 
 a noise minimization algorithm circuit, to:
 obtain the control voltage noise power from the noise power meter; 
 generate a correction parameter that minimizes the control voltage noise power; and 
 send the correction parameter to the oscillator; 
 
   
     wherein the phase noise generated by the oscillator is minimized by the correction parameter. 
   
   
       2 . The phase noise minimization circuit of  claim 1 , wherein the oscillator is a voltage-controlled oscillator. 
   
   
       3 . The phase noise minimization circuit of  claim 1 , wherein the feedback system is a phase-locked feedback loop system. 
   
   
       4 . The phase noise minimization circuit of  claim 1 , wherein the feedback system is a frequency-locked feedback loop system. 
   
   
       5 . The phase noise minimization circuit of  claim 1 , wherein the voltage noise present on the control voltage is analyzed up to a bandwidth of the feedback system. 
   
   
       6 . The phase noise minimization circuit of  claim 1 , further comprising:
 a lookup table to store a plurality of parameters calculated for different oscillation frequencies and process/voltage/temperature variations, the correction parameter being one of the plurality of parameters;   wherein the noise minimization algorithm obtains the correction parameter from the look-up table.   
   
   
       7 . The phase noise minimization circuit of  claim 1 , wherein the control voltage is a digital signal. 
   
   
       8 . The phase noise minimization circuit of  claim 1 , further comprising:
 an analog-to-digital converter to convert the control voltage to a digital signal, wherein the digital signal is analyzed by the calibration circuitry.   
   
   
       9 . The phase noise minimization circuit of  claim 1 , wherein the parameter is a digital control word and the oscillator is part of a switched capacitor circuit including a tank circuit of an LC oscillator, wherein the tank circuit receives the digital control word to coarsely select the output frequency. 
   
   
       10 . The phase noise minimization circuit of  claim 9 , the noise minimization algorithm further to:
 generate a second parameter based on the phase noise power;   
     wherein the second parameter is a digital tuning word to control a switched capacitor circuit of the noise filter to make the filter wideband. 
   
   
       11 . The phase noise minimization circuit of  claim 1 , the feedback system further comprising an AC-coupled transconductor and two digital-to-analog converters to generate two different DC biases, the transconductor and digital-to-analog converters to remove a voltage offset generated by device mismatches, wherein the two different DC biases are optimized by the calibration circuit to minimize flicker noise up-conversion by minimizing the control voltage noise power of the oscillator. 
   
   
       12 . The phase noise minimization circuit of  claim 1 , the feedback system further comprising a low dropout voltage circuit disposed between the calibration circuit and the oscillator, wherein the low dropout voltage circuit receives the parameter from the calibration circuit and generates a supply voltage, wherein the supply voltage minimizes power supply sensitivity of the feedback system. 
   
   
       13 . The phase noise minimization circuit of  claim 1 , the oscillator comprising a ring oscillator including two bias voltages, wherein two different DC biases are optimized by the calibration circuit to minimize flicker noise up-conversion. 
   
   
       14 . The phase noise minimization circuit of  claim 13 , further comprising a second ring oscillator and a multiplexer, wherein the calibration circuit uses the multiplexer to select either the first ring oscillator or the second ring oscillator, depending on which has a better symmetry. 
   
   
       15 . The phase noise minimization circuit of  claim 14 , further comprising a third ring oscillator, wherein the calibration circuit uses the multiplexer to select the first ring oscillator, the second ring oscillator, or the third ring oscillator, depending on which has a better symmetry. 
   
   
       16 . A feedback system, comprising:
 a feedback system comprising a voltage-controlled oscillator, the voltage-controlled oscillator to generate an output signal, the voltage-controlled oscillator to receive a control signal derived from a reference signal, wherein the control signal has a voltage noise power; and   a phase noise minimization circuit, comprising:
 a noise power meter to analyze voltage noise present on the control signal to determine the phase noise power of the voltage-controlled oscillator; and 
 a noise minimization algorithm circuit, to:
 obtain the voltage noise power from the noise power meter; 
 generate a correction parameter based on the phase noise power; and 
 send the correction parameter to the oscillator; 
 
   
     wherein the phase noise generated by the oscillator is minimized by the correction parameter. 
   
   
       17 . The feedback system of  claim 16 , further comprising:
 a lookup table to store a plurality of parameters, calculated for different oscillation frequencies and process/voltage/temperature variations, the correction parameter being one of the plurality of parameters;   wherein the noise minimization algorithm obtains the correction parameter from the look-up table.   
   
   
       18 . The feedback system of  claim 17 , further comprising:
 an analog-to-digital converter to convert the control signal to a digital signal, wherein the digital signal is analyzed by the noise power meter.   
   
   
       19 . The feedback system of  claim 18 , wherein the voltage noise on the control voltage is analyzed up to a bandwidth of the feedback system. 
   
   
       20 . The feedback system of  claim 19 , wherein control signal is a digital signal.