Calibration of voltage-controlled oscillators
View Patent ↗A calibration circuit ( 20, 50 ) and method ( 60 ) for calibrating the bias current of a VCO ( 10, 40 ) to minimize phase noise. The calibration circuit ( 20, 50 ) monitors the average voltage at the common-mode node of the VCO ( 10, 40 ) while varying the bias current over a predetermined range. The calibration circuit ( 20, 50 ) identifies the bias current associated with the minimum average common-mode voltage and utilizes this bias current for calibrating the biasing transistor of the VCO ( 10, 40 ).
1. A method of calibrating a bias current of a voltage-controlled oscillator to minimize 1/f 3 phase noise, comprising the steps of:
setting said bias current to a first predetermined value;
sampling an average value, corresponding to said bias current, of a common-mode voltage of said voltage-controlled oscillator;
varying said bias current by a predetermined amount towards a second predetermined value;
repeating said sampling and varying until an optimum bias current corresponding to an extreme value of said average value of the common-mode voltage is identified; and
calibrating said voltage-controlled oscillator using said optimum bias current.
2. The method of claim 1 wherein said first predetermined value is substantially equal to a maximum bias current associated with said voltage-controlled oscillator and said second predetermined value is substantially equal to a minimum bias current associated with said voltage-controlled oscillator.
3. The method of claim 1 wherein said first predetermined value is substantially equal to a minimum bias current associated with said voltage-controlled oscillator and said second predetermined value is substantially equal to a maximum bias current associated with said voltage-controlled oscillator.
4. The method of claim 1 wherein said extreme value is substantially equal to a minimum value of said average voltage at said common-mode node of said voltage-controlled oscillator.
5. The method of claim 1 wherein said extreme value is substantially equal to a maximum value of said average voltage at said common-mode node of said voltage-controlled oscillator.