Devices and methods of measuring gain of a voltage-controlled oscillator

1. A voltage-controlled oscillator gain measurement system, comprising: a voltage-controlled oscillator, configured in a phase-locked loop circuit, generating an output signal with an output frequency according to a control signal, wherein the control signal is generated according to the output signal divided by a scaling number; a voltage detector that is a differential analog-to-digital converter, configured to measure a voltage difference of the control signal; and a processor adjusting the scaling number to generate an output frequency difference of the output signal, and obtaining a reciprocal gain of the voltage-controlled oscillator by dividing the voltage difference by the output frequency difference.

2. The voltage-controlled oscillator gain measurement system of claim 1 , wherein the phase-locked loop circuit further comprises: a frequency divider, coupled to the processor, generating a feedback signal with a feedback frequency according to the output signal, wherein the feedback frequency equals the output frequency divided by the scaling number.

3. The voltage-controlled oscillator gain measurement system of claim 2 , wherein the phase-locked loop circuit further comprises: a phase detector, coupled to the frequency divider, generating an up/down signal by comparing a reference signal and the feedback signal; a charge pump, coupled to the phase detector, receiving the up/down signal to generate a current signal; and a filter, coupled to the charge pump, receiving the current signal to generate the control signal.

4. The voltage-controlled oscillator gain measurement system of claim 1 , further comprising: a switch, switched by the processor, coupling the control signal to a first node of the voltage detector to measure a first voltage and coupling the control signal to a second node of the voltage detector to measure a second voltage, wherein the voltage difference is the difference between the first voltage and the second voltage.

5. A method of measuring a gain of a voltage-controlled oscillator configured in a phase-locked loop circuit, comprising:

adjusting a scaling number to generate an output signal with a frequency of an output frequency plus an output frequency difference; measuring a first voltage of a control signal; adjusting the scaling number to generate the output signal with a frequency of the output frequency; measuring a second voltage of the control signal; and dividing a voltage difference that is measured by a differential analog-to-digital converter between the first voltage and the second voltage by the output frequency difference to obtain the reciprocal of the gain of the voltage-controlled oscillator, wherein the control signal is generated according to the output signal divided by the scaling number, wherein the output signal is generated according to the control signal.

6. The method of claim 5 , further comprising: controlling, by a processor, a frequency divider of the phase-locked loop circuit to adjust the scaling number.

7. The method of claim 6 , wherein the control signal is generated by a phase detector, a charge pump, and a filter, wherein an up/down signal is generated by the phase detector comparing a reference signal and a feedback signal, a current signal is generated by the charge pump according to the up/down signal, and the control signal is generated according to the current signal by the filter, and wherein the frequency divider generates the feedback signal by dividing the output signal by the scaling number.

8. The method of claim 5 , further comprising: coupling, by a switch switched by a processor, the control signal to a first node of a voltage detector to measure the first voltage; and coupling, by the switch switched by the processor, the control signal to a second node of the voltage detector to measure the second voltage.