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01/06/06 14:07
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 		 #106702 - why go for 20MHz
Responding to: ???'s previous message
with todays micros and HC chips you have risetimes in the order of 10ns. so a 20MHz scope will not see ringing/refelections if it dies within 3 oscillations.

I have once had to "reason" an oscillation too short for the scope to see and it was there (changes to remove the invisible made the thing work) but do you really want that much invisible to reason out?

Going for 100MHz is exactly the same, just need 5 times more care in circuit layout. Even at 20MHz you are unlikely to get by with a 2 layer board.

Of course, if the scope is for non-RF analog work 20MHz is probably excellent.

Erik

List of 87 messages in thread
TopicAuthorDate
20Mhz Analog Input of a DSO            01/01/70 00:00      
   Link            01/01/70 00:00      
      why go for 20MHz            01/01/70 00:00      
         No 4 layer PCB & faster ADC available            01/01/70 00:00      
      Initial look ...            01/01/70 00:00      
         Trigger Circuit            01/01/70 00:00      
            Try of explaination            01/01/70 00:00      
               Badly drawn            01/01/70 00:00      
               Trigger and Amp            01/01/70 00:00      
                  Take care...            01/01/70 00:00      
                     Speed            01/01/70 00:00      
                        Like This ?            01/01/70 00:00      
                           Just wait...            01/01/70 00:00      
                              so what do they do there ?            01/01/70 00:00      
                                 Direct Digital synthesis            01/01/70 00:00      
                                    I just can think about one benefit            01/01/70 00:00      
                     Searching...            01/01/70 00:00      
                        Misinterpretation            01/01/70 00:00      
                           Proper Op-Amp            01/01/70 00:00      
                              AD844 has 50 Ohm input resistance on -            01/01/70 00:00      
                                 inverting input resistance            01/01/70 00:00      
                              specifications            01/01/70 00:00      
                                 sampling            01/01/70 00:00      
                                    Of course            01/01/70 00:00      
                                       Yes but            01/01/70 00:00      
                                          Exactly!            01/01/70 00:00      
                                 Preamp Initial Schematic            01/01/70 00:00      
                                    please resubmit the schematic in a forma            01/01/70 00:00      
                                       Real size button            01/01/70 00:00      
                                          not quite good enough            01/01/70 00:00      
                                             Higher Resolution            01/01/70 00:00      
                                       Resize            01/01/70 00:00      
                                          I do not care if it fits, I can move it            01/01/70 00:00      
                                             readable with gthumb            01/01/70 00:00      
                                             They are1N4148s            01/01/70 00:00      
                                             Problem is at your end            01/01/70 00:00      
                                                do you refer to the first submit            01/01/70 00:00      
                                                   Web Browser            01/01/70 00:00      
                                                   Both            01/01/70 00:00      
                                    Some changes needed            01/01/70 00:00      
                                       have to sleep a little ,will post later            01/01/70 00:00      
                                       I would try this            01/01/70 00:00      
                                          not an analog eagle            01/01/70 00:00      
                                             Why not            01/01/70 00:00      
                                                not objecting, just wondering            01/01/70 00:00      
                                          Updated Schematic            01/01/70 00:00      
                                             FETs            01/01/70 00:00      
                                                I remember going to the races on Thursda            01/01/70 00:00      
                                                   Yes, Nowadays they're held at friday            01/01/70 00:00      
                                             Answers            01/01/70 00:00      
                                                JFET Input good            01/01/70 00:00      
                                                   Deviations            01/01/70 00:00      
                                             Answers II            01/01/70 00:00      
                                                Corrected mistakes            01/01/70 00:00      
                                                   Answers III            01/01/70 00:00      
                                                      RE : Answers III            01/01/70 00:00      
                                                      new questions about PCB/Supply            01/01/70 00:00      
                                                         Answers IV            01/01/70 00:00      
                                                            RE : Answers IV            01/01/70 00:00      
                                          How do adjust the cap trimmers?            01/01/70 00:00      
                                             Thanks for everything            01/01/70 00:00      
                     Found these            01/01/70 00:00      
            inductance            01/01/70 00:00      
               Relays            01/01/70 00:00      
                  Reed-relay            01/01/70 00:00      
                     Reed Relays            01/01/70 00:00      
         Plays no significant role            01/01/70 00:00      
            but they are sensitive            01/01/70 00:00      
               Analog Mux            01/01/70 00:00      
                  today Philips announced this MUX            01/01/70 00:00      
                  Strac capacitance make the worse            01/01/70 00:00      
                     Sorry, stray not strac            01/01/70 00:00      
   a better aproach maybe            01/01/70 00:00      
      PLD question            01/01/70 00:00      
         Re PLD questions            01/01/70 00:00      
            link            01/01/70 00:00      
            Go for CPLD or not !            01/01/70 00:00      
               Not in that timescale            01/01/70 00:00      
                  so about 10K gates are needed ?            01/01/70 00:00      
                     part numbers            01/01/70 00:00      
                        Wow pretty expensive !            01/01/70 00:00      
                  I'll have to wait till tommorow            01/01/70 00:00      
   is this helpful?            01/01/70 00:00      
      good link            01/01/70 00:00      
   Heres a start            01/01/70 00:00      
   'must read'            01/01/70 00:00      
      What a great reference !            01/01/70 00:00      

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