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i A PHYSICAL IMPLEMENTATION WITH CUSTOM LOW POWER ...

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The current source IFN, resistor RT and capacitor CT are used to model the charge<br />

storage and retention capabilities of the EEPROM [21]. The IFN is a current-controlled current<br />

source which senses the tunneling current GFN with a gain of unity. RT is chosen to be a very<br />

high value, so that most of the current IFN is supplied to the capacitor CT [21].<br />

The floating gate is modeled by the controlled source EFG. The value of the floating gate<br />

voltage is given by Equation 7-2 [21].<br />

fg, initial<br />

V fg = α dVd<br />

+ αsVs<br />

+ αcgVcg<br />

+ αbVb<br />

+ α tunVtun<br />

+ +<br />

Ct<br />

Q<br />

Equation 7-2: Expression for Floating Gate Voltage<br />

ΔQ<br />

The remaining part of the circuit is used to model Φsi, the surface potential of silicon<br />

under the tunnel oxide. The original description of the SPICE code as shown in the paper has<br />

been translated to HSPICE for use in HSPICE simulations. The HSPICE description of the<br />

macromodel is shown in Figure 7-11.<br />

The low-voltage and high voltage device models are based on the description given in<br />

[22]. The high voltage devices had an effective length of 1um and a tox (oxide thickness) of 275<br />

Angstrom [22]. The low voltage devices had an effective length of 0.35um and a thickness of 75<br />

Angstrom [22].<br />

125<br />

C<br />

t<br />

fg

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