Hi, I want to select a high frequency adc could sample a 5mV ac signal from 100KHz to 100MHz, which product would you suggest? Because I am new in this area, so could someone give me some detailed reason for selecting ADCs. Thank you so much.
At your frequencies of interest you should be able to amplify/boost your input signal with minimal distortion using either a differential ADC Driver Amp, or a higher turns-ratio transformer similar to the configurations described on AD9649 datasheet pg 18. If you choose the transformer route you will need to be sure its capable of operating without cut-off distortion down to your lowest 100kHz frequency target, as well supporting the bandwidth of your upper 100MHz target frequency.
Yes, the ADC will faithfully convert whatever differential voltage is applied to its inputs as long as the voltage level is within the allowable range of the ADC's inputs. The 14bit AD9649 has a full-scale input span of 2Vp-p which means at full-scale each output code represents 2V/16384 codes = 122uV. If your un-amplified Ain is only 5mV max you will only realize an output dynamic range of 5mV/122uV ~= 41 codes out of the possible 16384 ADC output codes available.
Most of our High Speed ADC's operate with nominal fullscale analog input spans of ~1-2Vp-p differential so in order to realize the full dynamic range from these converters you will need to first amplify/boost the level of your 5mV AC signal. A good general purpose 14bit ADC to start with is the AD9649-80 http://www.analog.com/en/products/analog-to-digital-converters/ad-converters/ad9649.html#product-overview
The AD9649 offers exceptional performance over the Analog Input frequency range you describe as illustrated in the various performance plots included in the datasheet. The product page also provides links to general ADC reference documents that will be helpful since you are new to data converter applications.
Thanks for your tips. You mentioned to amplified the signal, is there any danger to the signal that I want to extract? Is there any other way to capture the signal without making any change to it? Thank you.
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