Signal generating circuit and signal generating method

A device for estimating a gain of a controllable oscillator operated in a phase locked loop (PLL), the device comprising:

• a testing signal generator, arranged to inject a testing signal into the phase locked loop;
• and
• a time-to-digital converter (TDC), arranged to convert a phase difference between a reference clock signal and a feedback oscillating signal of the phase locked loop to a digital represented value for estimating the gain of the controllable oscillator, wherein the reference clock signal and the feedback oscillating signal are derived after the injection of the testing signal.

A method for estimating a gain of a controllable oscillator operated in a phase locked loop (PLL), the method comprising the steps of:

• injecting a testing signal into the phase locked loop;
• and
• converting a phase difference between a reference clock signal and a feedback oscillating signal of the phase locked loop to a digital represented value for estimating the gain of the controllable oscillator, wherein the reference clock signal and the feedback oscillating signal are derived after the injection of the testing signal.