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High Speed ADC with Bipolar Analog Input

Hello,

   I required an high speed ADC with bipolar analog input ranging from -V to +V. I was considering AD9042 but later on it came to my notice that it does not take in bipolar analog input. So, right now I am considering the following ADC's for the same purpose:

1. AD9246

2. AD9254

3. AD6645

      I do not have any information yet regarding whether these devices take in bipolar analog input or not. I request you to inform me whether any of these devices fulfills my requirement.

Thanks

Regards

Darshil Patel

  • Hi Darshil,

    Thank you for your interest in ADI parts. All the ADCs in your list have differential inputs. Are you OK with differential inputs?

    Thanks,

    Doug

  • Hello Doug!

    Thanks for your reply. Correct me if I am wrong. As far as I understand, differential input means that difference of two incoming signal will be taken as input. However, that does not necessarily mean that it will take in positive and negative analog signals as input. I need an ADC which can have say -5V to +5V input range with around 50MHz analog input bandwidth.

    I am not sure if differential and bipolar are the same thing. Please help me fill in this gap in my knowledge.

    Also please do suggest me any high speed bipolar ADC if present.

    Thanks

    Darshil Patel

  • Hello Darshil,

    There are two analog inputs at ADC, named VIN+, VIN- that are in 180 degree difference. We can drive ADC either at the single-ended(using one of two inputs) or at differential (using both inputs). However, a differential inputs driving is suggested to achieve the optimum performance through high common-mode rejection and so on.   

    Analog input range is limited by internal circuit including supply voltage and it is specified in "Analog Input" section on datasheet.  It is mostly 1Vp-p or 2Vp-p differential (half of this voltage swing at each input) for most high speed ADCs( AD9246, AD9254 : 1Vp-p to 2Vp-p range, AD6645:2.2Vp-p). If there are beyond this full-scale level at Analog Inputs, we can't avoid performance degradation and there can be reliability issue some cases.

    There are some ADCs at sample rage for wide Vin range (for example, AD7626) but I don't see any high speed ADCs that allow -5V to +5V input range.

    The parts you are considering don't support 10Vp_p in -5V to +5V input range. You can do ADC product search by specifying parameters at the  link below and below is the screen shot as example.  

     

    http://www.analog.com/en/parametricsearch/10826#/p193=|3|12|14|16&p1746=40000000|26000000000&p3062=|1|6&p4913=1|8.192&sel=row12|row98|row117

    Thanks

    Tony

  • Hi Darshil,

    I agree with what Tony said. Yes, differential input means that the difference of the two input signals determines the ADC differential input amplitude. The differential amplitude is the voltage on one input referenced to the other differential input (not referenced to ground). So, with differential inputs you can have a negative input voltage with both input signals being positive with respect to ground.

    It sounds like you are looking to convert a single-ended signal that is from -5V to +5V with respect to ground. The ADCs I am familiar with will have problems applying a voltage that goes more negative than the ground reference.

    One possibility is to use an amplifier such as ADA4932 with its supplies connected to +5V and -5V. This could do the single-ended-to-differential conversion (and attenuation, gain <1) so the signal will be compatible with an ADC with differential inputs.

    Thanks,

    Doug