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Honored Contributor I

Interfacing Terasic THDB_ADA Daughter Card with Cyclone III Starter Kit

I have a terasic thdb_ada Daughter Card alongwith my cyclone iii fpga starter kit. But due to the very poorly made User manual for the THDB_ADA Board, I need to know the answers to the following questions, before I can start interfacing Analog signals. 


Q1) What is the analog input voltage range that we can supply to this board as input ? (I don't wish to directly supply my 10V analog signal & burn the board) 

Q2) Since we have 2 separate AD channels, can we supply 2 independent differential signals at these, or do they need to have a common ground (single-ended) ?
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2 Replies
Honored Contributor I


Q1)User manual is not so bed in my opinion. In CD you will have datasheets of AD converters with maximum allowable input voltages. But as I remember maximum input voltage for AD is plus and minus 1 V refered to ground.  


Q2)You should have a schematic on mentioned CD. AD converters have differential inputs but special transformer is used to convert single-ended signal to differential input of AD. Inputs have common ground plane - I mean SMA connectors. 


Best regards
Honored Contributor I

Thanks for responding komi ... 

I asked the same questions to Terasic-support, and even they replied that the "analog-input voltage range is 2vp-p". 


But what exactly does a 2Vp-p translate to: (-1V to +1V) or (0V to 2V) or anything else? 


You have quoted it as (-1V to +1V), but my observations into the AD datasheet (AD9248) that came along with the CD suggest something different.  

There, in the Absolute Maximum Voltage Rating section, VinA & VinB have absolute minimum voltage of -0.3v. Also ... the datasheet mentions an example where they mean (0V to 2V) by 2Vp-p. (pics attached). 


Of course, one can argue that these ratings refer to the actual A/D IC, and not our THDB_ADA inputs directly. There's a lot of interfacing circuitry in between. 


This makes us closely scrutinize the board-schematic on the mentioned CD. There, the circuit between the SMA connector & An-Inputs to A/D IC, just resembles some filter. (no voltage scaling seen) 


So I guess, finally - the analog inputs that we can give to the SMA connectors must be between (0v to +2v). What say ?