Patent ID: 7750684

Claim:
A power-on detection circuit for detecting a minimum operational frequency, comprising: an oscillating circuit, for generating an oscillating signal having an upper threshold, comprising; a ring oscillator, for generating a first oscillating signal up to the upper threshold; and a high pass filter, coupled to the ring oscillator, for filtering the first oscillating signal to generate a second oscillating signal, wherein a logic signal is generated once the first oscillating signal reaches the certain frequency; and a rectification device, coupled to the oscillating circuit, for receiving the second oscillating signal and generating the logic signal once the first oscillating signal reaches a certain frequency, comprising: a transistor, having a gate coupled to the high pass filter and a source coupled to a first reference voltage; a resistor, coupled between a second reference voltage and a drain of the transistor; and a logic detect circuit, coupled to the drain of the transistor, for outputting the logic signal when the transistor is turned on by the second oscillating signal.