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U. Glaeser

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FIGURE 2.24 Read only memory (ROM) circuit.<br />

by cutting the connection between the drain of the MOSFET and the column (bit) line. ROMs are effective<br />

in applications where large volumes are required.<br />

Low-Power CMOS Circuit Design<br />

The increasing importance and growing popularity of mobile computing and communications systems<br />

have made power consumption a critical design parameter in VLSI circuits and systems. The design of<br />

portable devices requires consideration of the peak power for reliability and proper circuit operation,<br />

but more critical is the time-averaged power consumption to operate the circuits for a given amount of<br />

time to perform a certain task [11,12]. There are four sources of power dissipation in digital CMOS<br />

VLSI circuits, which are summarized in the following equation:<br />

where<br />

Pavg Pswitching © 2002 by CRC Press LLC<br />

P avg = P switching + P short-circuit + P leakage + P static<br />

= C LVV DDf + I scV DD + I leakageV DD + I staticV DD<br />

= C LV 2 f + I scV DD + I leakageV DD + I staticV DD<br />

= time-averaged power<br />

= switching component of power<br />

Pshort-circuit = short circuit power dissipation<br />

Pleakage = leakage power<br />

Pstatic = static power<br />

CL = load capacitance<br />

V = voltage swing (and in most cases this will be<br />

the same as the supply voltage VDD) f = clock frequency<br />

Isc = short-circuit current<br />

Ileakage = leakage current<br />

= static current<br />

I static

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