I designed the following 2T XOR cell for my full adder purpose:

enter image description here

Theoretically it gives correct output for all input combinations. But on Tanner Eda using 180nm technology 5V supply, it gives logic 1 for input combination a = 1, b = 1 but theoretically it is incorrect. Because PMOS OFF for input logic 1 so output must be zero.

enter image description here

How can I make my 2T XOR cell fully functional for all input combinations?


1 Answer 1


you have not connected the body/bulk connection properly in your schematic. PMOS to VSS. But that circuit leaves the output node floating for the A=B=1 condition. Scan through the various solutions here, there is a robust TG version of XOR and XNOR, it uses 4 transistors though.

If you look at all the possible states, you have 2 transistors each in 2 states for 4 possible combinations. There will always be one combination in which both transistors are off and thus the output node will float.

  • \$\begingroup\$ thanks placeholder for sending link of logic wiki which quite informative:)But Why output node of XOR logic is float however 0 is pass through both transistor. Can you please more elaborate this concept. \$\endgroup\$
    – GiLL
    Aug 19, 2014 at 4:54
  • \$\begingroup\$ First it is NOT an XOR as you've shown with your simulation. When A = B = 1 both transistors are off and teh output is not driven (i.e. it is floating) \$\endgroup\$ Aug 19, 2014 at 9:15

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