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Method and low-power circuits used to generate accurate drain voltage for flash memory core cells in read mode

  • US 6,292,399 B1
  • Filed: 07/03/2000
  • Issued: 09/18/2001
  • Est. Priority Date: 07/03/2000
  • Status: Expired due to Fees
First Claim
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1. A control circuit for generating an accurate drain voltage for selected memory core cells in a semiconductor memory circuit during a Read mode of operation, said control circuit comprising:

  • selected gate transistors each having its conductive path being coupled between a power supply voltage and a drain of one of the selected memory core cells;

    differential amplifier means responsive to a bitline voltage corresponding to a drain voltage of the selected memory core cells and a reference voltage for generating a select gate voltage which is decreased when the bitline voltage is higher than a target voltage and which is increased when the bitline voltage is lower than the target voltage;

    said differential amplifier circuit means including a first input transistor having its gate connected to a stable reference voltage and a second input transistor having its gate coupled to a feedback voltage which is proportional to the bitline voltage, the second input transistor having its collector providing the select gate voltage;

    a capacitor divider network formed of a first capacitor and a second capacitor connected in series between the bitline voltage and a ground potential, the junction of said first and second capacitors providing the feedback voltage;

    source follower circuit means responsive to the select gate voltage for generating the bitline voltage which is maintained at the target voltage;

    said source follower circuit means being formed of a plurality of transistors whose drains are coupled together and to the power supply potential, gates are connected together and to receive the select gate voltage, and sources are connected together and to provide the bitline voltage; and

    the control gates of the select gate transistors being connected to receive said select gate voltage for maintaining the voltage at the drain of the selected memory core cells to be approximately constant.

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