basic question about ADC

[tech_pro]

Hi

i want to ask a very basic question

i have a signal of range 0-5 V (analog )

that is to be digitized on a speed of at least 50MHz and i m unable to find ant ADC in this range

so i have to attenuate the window in 0-2 V

wat could be the possible effects of this attenuation on acurracy of the digitized data

regards
uzmeed

 

[keith1200rs]

Most fast ADCs don't work on 5V and a lot need a differential input, particularly the higher resolution devices. You can reduce the signal level to drive the ADC but you will need to buffer it as most high speed ADCs want a low impedance signal source.

Keith

 

[tech_pro]

i hav to find the direction of the signal by comparing them digitally

how much effect it could make on the direction estimation by reducing the window

and my question is there wat will be the overal effect on the system performance

regards
uzmeed

 

[allanvv]

You lose about one bit of resolution by going from 5V to 2V. The effect of noise will be approximately doubled. You'll also need more circuitry to buffer the attenuated input signal like Keith said, which can add more noise/errors.

 

[keith1200rs]

If all you want to do is compare a signal then a DAC and comparator would be a simpler solution, although without knowing the rest of the design criteria it is impossible to be certain.

Keith.

 

[tech_pro]

Hi

thank u for the suggestion

infact the design is that the analog data from the sensor is to be digitized and digital data is fed into the FPGA to compute the direction

u can say that the amplitude of different sensor is copared for direction estimation

but the problem is that the output of the sensor is 0-5V

and the ADC i could find does not fall in this category

i hope u can help me more now

regards
uzmeed

 

[keith1200rs]

You need to pick you ADC - ignoring the 0-5V issue. Then add circuitry to scale the signal. If the ADC is single ended input then a couple of resistors and a buffer might be all that is needed. If it is differential input then you need something like the LTD1992 to provide single ended to differential conversion as well as the scaling.

Keith.