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Michael Karas
11/08/11 09:00
Read: 367 times
Beaverton Or

#184588 - Impedance With Divider
Responding to: ???'s previous message
If you must use a resistor divider to scale the signal then in this case you want to get the source impedance as low as possible and the ADC/MUX load impedance as high as possible. Then hope that the parallel resistance of the two resistors in the divider is greater than 10->100X the source impedance and that the ADC/MUX impedance is greater than 10->100X the parallel divider resistance. The 10-100X factors are seat of the pants guidelines for simpler applications where the utmost in precision is not needed.

If it is not possible to come close to the above then the solution is to insert an OPAMP stage to provide the scaling and present a low impedance source to the ADC/MUX component.

Michael Karas

List of 13 messages in thread
Looking for 8051 that supports high speed I2C      John M      11/02/11 15:22      
   SPI      Per Westermark      11/02/11 16:06      
      gotcha      John M      11/02/11 21:03      
         3.4 MHz I2C      Andy Peters      11/04/11 13:13      
            RE: SPI is simpler      Andy Neil      11/04/11 14:03      
               One other quick question for all you smart people.      John M      11/07/11 20:24      
                  Some things to consider....      Michael Karas      11/08/11 05:11      
                     Full range and clipping      Per Westermark      11/08/11 05:24      
                        Impedance      John M      11/08/11 06:04      
                           You sure?      Per Westermark      11/08/11 06:18      
                           Impedance With Divider      Michael Karas      11/08/11 09:00      
                           Impedance matching      Andy Neil      11/08/11 15:54      
   if I recall      Erik Malund      11/03/11 07:13      

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