| ??? 04/17/06 12:40 Read: times |
#114383 - Re: Prepared to make a mistake Responding to: ???'s previous message |
Dear Russell,
Thanks for your reply. Prahlad, this is obviously a commercial product and you as the engineer have to make the decisions. Yes, It is a very low volume commercial product. You are right Russell, I have to start making decisions on my designs rather than depending on others to help. I realise that I cant continue this practice forever. But still I think it is the learning stage for me and not the maturity so I put the designs here for comments by analog experts like Kai and believe me I am not just applying the suggestions blindly but understand and then do the things so that next time I dont need to ask the same thing again. My products are too low volume type to experiment and learn and I cant sell my customer a product that doesnt work well. I've put three products I've designed through the full CE testing and one failed due to the transzorb failing. Thanks for sharing your experience and boosting my morale. I always thought its only me who make so much mistakes in design! Is the filtering adequate or too much? What are you trying to achieve? Best analog performance? CE (or other) emissions & susceptance?. You must have a fixed goal. I am not targeting any compliance test like CE my aim is to get best analog performance. Do you need to make changes? Perform some testing, that will guide you. Do you mean changing filter section components to see the effect. The 7660 is a charge pump - I'd be keeping that away from low level analog stuff. Can it create trouble? If you suspect it can, then maybe you should look closer at it. For the -ve supply - what ripple on the supply can your application tolerate? What is the PSRR (power supply rejection ratio) of the op-amp? Then measure the ripple on the supply - that should answer that question. I can calculate the ripple using the formulas given in the datsheet of ICL7660 but the output of ICL7660 that contains ripple isnt fed directly to opamp [ TLC2274] it is applied to LM2937 LDO and output of LDO goes to OpAmp. I dont know how to relate ripple with PSRR of opamp can you please give some links. I am targetting 10 bit accuracy - then you'd best be using a converter with better than 10bit resolution! Saying you want 10bit accuracy doesn't tell us much - at DC it may be quite simple, at 1GHz it might be bleeding edge. My micros internal ADC have 10 bit resolution and I do understand accuracy and resolution are two diffrent things. When I said I want 10 bit accuracy I was speaking with reference to my analog layout and not converter. I want my analog section design to give 10 bit or better so that the error due to analog section is negligible when compared to overall error of covnertor. Qualify and quantify. Repeat after me, 'qualify and quantify'
Qualify and Quantify Thanks & Regards, Prahlad Purohit |
