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Design >> Analog Design >> Difference between two inverters
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Message started by somisetty on Jun 16^th, 2009, 1:40am

Title: Difference between two inverters
Post by somisetty on Jun 16^th, 2009, 1:40am

Hi all,

what are the advantages and disadvantages between these two inverters?

Thanks

Title: Re: Difference between two inverters
Post by raja.cedt on Jun 16^th, 2009, 5:15am

hi,
both are same ,you can't keep nmos drain potential less than source potenial

Thanks,
rajasekhar.

Title: Re: Difference between two inverters
Post by uu@uk on Jun 16^th, 2009, 10:19am

Hi,

The first one is the source follower. it is better to use to drive resistor and it cannot give you rail to rail output. The second one is usually the inverter driving capacitor and easily get a rail to rail output. Also, the second one, is saving power.

Title: Re: Difference between two inverters
Post by raja.cedt on Jun 16^th, 2009, 10:22am

hi,
have you locked at both schematics, as soon you connect nmos on the bottom side immediately low potential point will be the source and remaining will be the drain....so how second ckt is possible?

Thanks,
Rajasekhar.

Title: Re: Difference between two inverters
Post by thechopper on Jun 16^th, 2009, 6:31pm

uu@uk wrote on Jun 16^th, 2009, 10:19am:

In addition the second one has a large gain, therefore it reduces the delay between input an output signal provided both drive the same load.

Title: Re: Difference between two inverters
Post by aamar on Jun 16^th, 2009, 11:35pm

It can not be a source follower, what rajasekhar wrote is correct. It is just a matter of flipping the symbol in the schematic but remains the PMOS connected to the highest voltage in the circuit and the NMOS to the lowest voltage. Assuming that the transistors are layouted symetrical so that the source and drain area of each transistor are equal.

In order to have a source follower then you have to connect the NMOS to the VDD and the PMOS to the VSS.

Best regards,

aamar

Title: Re: Difference between two inverters
Post by raja.cedt on Jun 17^th, 2009, 1:08am

hi aamar,
ya thats what even i am arguing.. And for the second argument it wont properly work as Source follower also, it shows hysteresis.

thanks,
rajasekhar.

Title: Re: Difference between two inverters
Post by aamar on Jun 17^th, 2009, 2:20am

Yes rajasekhar, you are right, I meant just the principle but not that it is the optimum one.