| Jinhong Wang wrote: |
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Hi, Stefan, I see in your ppt "Design and performance of 6 GSPS waveform digitizing chip DRS4" , you define DRS4 ENOB as 1Vpp/0.35mv(RMS) = 11.5bit, where, 1Vpp is the linearity input range, and 0.35mv is the rms voltage after offset correction. What I understand is that 0.35mV is obtained from DC offset Correction, hence 11.5 bit is for DC input, am i right? If true, what about ENOB for AC input in the whole analog bandwidth? thanks~
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The expression ENOB for 1Vpp/0.35mV(RMS) is wrong, but I learned this later. Now I call it SNR. The ENOB is calculated in a more complicated way, see for example http://en.wikipedia.org/wiki/ENOB. If you measure the ENOB without timing correction, it's pretty poor (in the order of 7-8 bits). This is because without timing calibration, a sine input has huge side bands, and the ENOB involves the power of your signal over the power of the side bands. If you do a proper timing calibration, you spectrum gets "sharper", and hence the ENOB increases. But I have to admit that I never measured it carefully, since we are still optimizing the timing calibration. Once we have a perfect timing calibration, I will do it and update the data sheet. |