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i A PHYSICAL IMPLEMENTATION WITH CUSTOM LOW POWER ...

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7.2.5 Power Multiplexer<br />

Figure 7-16: Level Shifter and Pass Transistor for Column Latch<br />

The design of the power multiplexer is based on the patent US 7,005,911 [27]. As the EEPROM<br />

erase and program operations are high voltage operations, and the read being a low voltage<br />

operation, it is necessary to have a power multiplexer which could choose between the high and<br />

low voltages depending on the operation performed.<br />

Such circuits are essential at the input to the word-line level shifter. The<br />

level shifter<br />

would receive a high voltage from the power multiplexer for an erase and program operation and<br />

a low voltage for a read operation.<br />

Power multiplexers are also used to connect to the column gates, which output a high<br />

voltage during the erase operation, a ground voltage during program operation and a low voltage<br />

during a read operation. Figure 7-17 shows the schematic of the power multiplexer used in the<br />

design. The LS1 and Vdd_switch as shown in Figure 7-17 are essentially level shifters used to<br />

shift the output to Vpp or Vdd depending on the enable<br />

input.<br />

133

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