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Shadow RAM Cell and Shadow RAM

IP.com Disclosure Number: IPCOM000101755D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Peterson, CW: AUTHOR

Abstract

Fig. 1 is the schematic for a radiation-hardened static RAM (rad hard SRAM) cell. Because it is a balanced design, when power is applied (power-on state) there is an equal probability that the cell will come up with T high and C low, a "1," or C high and T low, a "0." This is typical for SRAM cells today, whether rad hard or otherwise.

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Shadow RAM Cell and Shadow RAM

       Fig. 1 is the schematic for a radiation-hardened static
RAM (rad hard SRAM) cell.  Because it is a balanced design, when
power is applied (power-on state) there is an equal probability that
the cell will come up with T high and C low, a "1," or C
high and T low, a "0."  This is typical for SRAM cells today, whether
rad hard or otherwise.

      This SRAM cell can be designed with an imbalance to
predetermine its power on state by placing the resistor in only one
side of the cell.  With a resistor in one side the cell will always
power up as a "1," see Fig. 3, and with the resistor in the other
side of the cell will always power up as a "0," see Fig. 2.  Data
or instructions could be stored in an array made up of these one and
zero cells the same way data is stored in a read only store (ROS).
On power-up the array would act like a ROS because the array cells
would power up with the prestored data or instructions loaded in the
array.  After power-up the RAM array would behave like an ordinary
rad hard memory array.  The result is a SRAM with information faintly
impressed on it, a shadow RAM.

      The shadow information can also be recovered for any cell or
group of cells by resetting that cell or group of cells.  To reset
cells, drive WL high then pull both BLT and BLC high or low for a
period of time (determined by Rp).
      The advantages of this over other alternatives are:
      Easily EC'able -- A cou...