| ??? 03/09/06 22:09 Read: times Msg Score: +1 +1 Good Answer/Helpful |
#111785 - Add the second stage... Responding to: ???'s previous message |
So you have a 3 element filter instead of a 5 element? Do you understand what that Low Pass Filter is used for? The low pass filter has to get rid of 3 main frequencies that are also present in the output: Clock Frequency, Clock Frequency - Out Output Frequency, and Clock Frequency + Output Frequency. You need at least a 5 element chebychev or eliptical filter on the output to ensure that these signals are attenuated sufficiently. Removing a section of the filter is a bad idea. In fact, you may want to add a section for a 7 element filter. You need the cuttoff frequency of the filter well below the "Clock Frequency - Maximum Output Frequency" or you will have these signals mixed in as well. Also make sure that you design the filter for the load that it's looking (terminating) into. BTW, you should terminate the output side of the filter with a non-inductive resistor equal to the designed load, or your not going to get any accurate data on the scope. Also, a spectrum analyzer would be a more appropriate tool if you have one available. A scope really doesn't tell you a whole lot here...
Trev |
| Topic | Author | Date |
| AD9835 noise problem | 01/01/70 00:00 | |
| noise | 01/01/70 00:00 | |
| Recommendations | 01/01/70 00:00 | |
| quick fix? | 01/01/70 00:00 | |
| Maybe | 01/01/70 00:00 | |
| Transmission lines | 01/01/70 00:00 | |
| 5MHz? | 01/01/70 00:00 | |
| Spectrum analyser | 01/01/70 00:00 | |
| It's ground noise | 01/01/70 00:00 | |
| ground noise and groundhogs | 01/01/70 00:00 | |
| Harmonics as well | 01/01/70 00:00 | |
| comments | 01/01/70 00:00 | |
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| Splitting the ground plane | 01/01/70 00:00 | |
| Evaluation board | 01/01/70 00:00 | |
| thin ground? | 01/01/70 00:00 | |
| that is why you use star | 01/01/70 00:00 | |
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| Would do! | 01/01/70 00:00 | |
| does not exist, Jan if you used twisted | 01/01/70 00:00 | |
| The clock signal? | 01/01/70 00:00 | |
| oh well | 01/01/70 00:00 | |
| Indeed | 01/01/70 00:00 | |
| is there a way... | 01/01/70 00:00 | |
| Hardly | 01/01/70 00:00 | |
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| twisted pair | 01/01/70 00:00 | |
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| No no... | 01/01/70 00:00 | |
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| What clock | 01/01/70 00:00 | |
| ? | 01/01/70 00:00 | |
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| But... | 01/01/70 00:00 | |
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| even better | 01/01/70 00:00 | |
| Good trick! | 01/01/70 00:00 | |
| same point | 01/01/70 00:00 | |
| Both | 01/01/70 00:00 | |
| I feel strong now! | 01/01/70 00:00 | |
| Funny! | 01/01/70 00:00 | |
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| Oh Dear | 01/01/70 00:00 | |
| NO analog outputs | 01/01/70 00:00 | |
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| Publishing failed | 01/01/70 00:00 | |
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| corrections | 01/01/70 00:00 | |
| Big test | 01/01/70 00:00 | |
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| Answers | 01/01/70 00:00 | |
| University of Kai | 01/01/70 00:00 | |
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| of course | 01/01/70 00:00 | |
| Update | 01/01/70 00:00 | |
| Eager to know | 01/01/70 00:00 | |
| Me too | 01/01/70 00:00 | |
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| Electronic World Feb 06 | 01/01/70 00:00 | |
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| Interesting question | 01/01/70 00:00 | |
further interesting question | 01/01/70 00:00 |