Difference between pseudo differential and differential ADC

Question

Hello everybody, 
 I'm facing some existential questioning and I'd be happy and relieved if someone come along with me in my quest. 
 I'm using the AD7451 a 12 bit pseudo differential ADC in my design to better cancelation of common mode noise as my sensing and processing functions are on two separate boards. 
 I now want to change to an AD7450 the differential version to convert a differential signal. Here is my question. How come one is differential and other fully differential while their respective datasheets show the same internal structure? 
 http://www.analog.com/static/imported-files/data_sheets/AD7450.pdf 
 http://www.analog.com/static/imported-files/data_sheets/AD7441_7451.pdf 
 Thank you guys.

ClaireL · Accepted Answer

Hi arocklife, 
 The result of the conversion process on a pseudo differential part is equivalent to (Vin+ - Vin-). This is much like differential, except that the negative input terminal is DC rather than a sinewave. There is a limited voltage range on the Vin- terminal, it is normally ground. This effect of this is that the signal ground is seperated from the ADC ground. If there is common noise on the signal and the signal ground, this will be rejected by a pseudo differntial part. The comparator is internally setup to accept these types of signals. 
 Regards, 
 ClaireL.

ClaireL · Answer

Hi arocklife, 
 Yes, the internal structure of the AD7450 and the AD7451 are very similar. For the purposes of describing the input structure on the datasheet, they are identical. The only difference in the AD7451 Vin- input needs to be tied to a DC input. 
 If you are looking to use the AD7450, also consider the AD7450A which is a similar part. The differences are that the AD7450A is available in a smaller package and it has slightly better specifications than the AD7450. 
 Regards, 
 Claire.