with self oscillating pulse width modulators , using a hysteretic comparator to change the output duty cycle according to the input signal , as often used for example for class - d amplifiers or switching regulators , the frequency varies with output power and supply voltage . the disclosed invention presents a method to drastically reduce the frequency variation by introducing the combination of an analog and a digital feedback loop to shift the hysteretic threshold , ideally by providing a single absolute value , which is proportional to the pulse frequency and by alternating the polarity of shifting the hysteretic threshold , based on the actual output pulse phase .