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Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
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Posts: 874
Hi Does not having the ref pin on a signal chip ADC effect much of the sampling. Do you connect it to the Vdd or ground. Is there any reason to connect it?
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
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Posts: 1155
It provides two major functions: 1.) Matching the rail-to-rail swing of the signal source to maximize bit-depth resolution 2.) Providing accurate conversion results with a voltage reference (16bit and above usually require this setup)
In most cases a 8 to 12 bit A2D will just use VCC as linear regulators have minimal noise... with a cap...
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
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Thanks wasn't shore if it could be left out, wired it in. Just connected it straight to Vdd. Would it be better to have a inductor or capacitor wired in parallel or series to help.
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
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Hi Bjorn
The MCP3550/1/3 devices accept single-ended reference voltages from 0.1V to VDD. Since the converter output noise is dominated by thermal noise, which is independent of the reference voltage, the output noise is not significantly improved by diminishing the reference voltage at the VREF input pin. A reduced voltage reference will significantly improve the INL performance (see Figure 2-4); the INL max error is proportional to VREF 2.
Will add a separate wire thought, just curious why it say it won't do much?
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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You can set the reference voltage to what you want to call maximum. If your chip takes 5.1v you can set the reference to 5v. Here, 5v will correspond to the maximum number of bits set high for the ADC. If it is a 10-bit ADC you will have 1023 as the value.
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
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Thanks Iamsmooth, Would it still have a value of 1023 if the voltage was half of what the chip takes, or is the 1023 for the max. I was under some impression that it wasn't necessary to connect the reference pin(just used to improve sensitivity), but I'm guessing it won't work without it.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
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An important use of the ref pin is for ratiometric applications. If you excite your transducer *and* reference your ADC to the same voltage, then reference drift disappears from the errors, handy for weighscale or thermometer applications.
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ADC and ref pin
