Calculating a parasitic capacitance of an oscillator circuit
AssigneeEchoStar Technologies L.L.C.
InventorsLeslie Carmichael, Michele Stein
Life of this patent
Estimating the term…
Abstract
Described herein are techniques for determining a board parasitic capacitance of a crystal oscillator circuit. A crystal's frequency is measured under load condition off-circuit. After coupling the crystal to the oscillator circuit, external capacitors may be adjusted to produce frequencies approximating the off-circuit measurement with upper and lower margins. Calculation of the load capacitor values at the exact frequency measured off-circuit allows for derivation of the board parasitic capacitance by subtracting the calculated capacitor values from the original total load value used in the off-circuit measurement.
Claims14
A method for determining a parasitic capacitance of an oscillator circuit, the method comprising:
- identifying a total load capacitance for an oscillator circuit;
- measuring a first frequency of an oscillator crystal separate from the oscillator circuit at the total load capacitance;
- measuring a second frequency of the oscillator crystal coupled to the oscillator circuit, the oscillator circuit including at least one first capacitor having a first capacitor value;
- measuring a third frequency of the oscillator crystal coupled to the oscillator circuit, the oscillator circuit including at least one second capacitor having a second capacitor value that is different than the first value;
- determining a third capacitor value, for use in the oscillator circuit, to cause the oscillator circuit to produce the first frequency, the third capacitor value determined based on the first frequency, the second frequency, the third frequency and the first and second capacitor values;
- and
- determining a parasitic capacitance of the oscillator circuit based on the third capacitor value and the total load capacitance.
A method for determining a parasitic capacitance of an oscillator circuit, the method comprising:
- measuring a first frequency of an oscillator crystal separate from an oscillator circuit under expected load conditions of the oscillator circuit;
- coupling the oscillator crystal to the oscillator circuit;
- measuring a second frequency of the oscillator crystal with a first set of capacitors in the oscillator circuit;
- measuring a third frequency of the oscillator crystal with a second set of capacitors in the oscillator circuit;
- determining a capacitor value, for use in the oscillator circuit, that comprises part of a load of the oscillator circuit under the load conditions to produce the first frequency of the oscillator circuit, the capacitor value determined based on the first frequency, the second frequency, the third frequency and the first and second capacitor values;
- and
- calculating a parasitic capacitance of the oscillator circuit based on the first frequency, the second frequency, the third frequency and values of the first and second sets of capacitors.
A method for determining a parasitic capacitance of an oscillator circuit, the method comprising:
- identifying an expected load capacitance (Ctotal) of an oscillator circuit;
- measuring a first frequency (F1) of an oscillator crystal separate from the oscillator circuit under the expected load capacitance (Ctotal);
- coupling the oscillator crystal onto the oscillator circuit;
- selecting a first set of capacitors (Cv1) for the oscillator circuit;
- measuring a second frequency (F2) of the oscillator crystal with the first set of capacitors (Cv1);
- selecting a second set of capacitors (Cv2) for the oscillator circuit;
- measuring a third frequency (F3) of the oscillator crystal with the second set of capacitors (Cv2);
- and
- calculating, by computer, a parasitic capacitance (Cpara) of the oscillator circuit based on F1, F2, F3, Cv1 and Cv2.
Dependencies are inferred from the claim text.