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Power-on detection circuit for detecting minimum operational frequency

  • US 7,750,684 B2
  • Filed: 04/18/2008
  • Issued: 07/06/2010
  • Est. Priority Date: 04/18/2008
  • Status: Active Grant
First Claim
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1. 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.

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