Dynamic Logic- III - Domino CMOS limitations. - only non...

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Domino CMOS – limitations. - only non – inverting structures can be implemented. - Charge sharing between dynamic stage output node and intermediate nodes of nMOS block during evaluation phase.
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C2 comparable in size with C1. Assume all inputs are low initially and C2 has an initial value of ‘0’. During precharge phase C1 charged to VDD. When input of upper nMOS makes a ‘0’ – ‘1’ transition in evaluation phase charge stored in C1 shared by C2, the output voltage after charge sharing becomes VDD/(1+C2/C1). If C2 = C1 voltage becomes VDD/2. Important to have C2 much smaller than C1.
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A weak pMOS (smaller W/L) device in feedback used to prevent loss of output voltage. Weak pMOS turned on only when the precharge node is kept high.
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Use separate pMOS transistors to charge the intermediate nodes. The pre-charging of all high-capacitance nodes within the circuit eliminates potential charge sharing problem. Could add delay. -Multioutput
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Multioutput CMOS domino gate
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Multioutput CMOS domino gate C1 = G1 + P1C0 C2 = G2+P2G1 +P2P1C0 C3 = G3 +P3G2+P3P2G1+P3P2P1C0 Carry look ahead
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NORA CMOS Logic The name comes for NO RAce property of The name comes for NO RAce property of this class of dynamic logic circuits. this class of dynamic logic circuits. The logic functions are implemented using The logic functions are implemented using n n - - type and p type and p - - type dynamic CMOS and type dynamic CMOS and C C 2 MOS blocks. MOS blocks.
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This note was uploaded on 09/24/2010 for the course EEE MEL G621 taught by Professor Gurunarayanan during the Fall '08 term at Birla Institute of Technology & Science, Pilani - Hyderabad.

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Dynamic Logic- III - Domino CMOS limitations. - only non...

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