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We are using PIC32MZ series Microcontrollers for our energy based application where we are measuring voltage and current for electric consumers. One single meter can monitor current for upto 10 consumers hence we used multiple pin interface to the ADC. The current ADC resolution is 12 bits which I guess is fine.

Now what I read online, Sigma Delta ADCs are suited better to measure power esp in low frequency range because they give more accurate reading and they can filter out noise from transmission lines. The problem is most MCU come with SAR ADCs (which work fine generally) but in our case I think Sigma Delta would suit us better, the problem is Sigma Delta are usually dedicated and does not have channels (we need 12 channels at least).

What is your proposed solution in my case? My question is, it is worth going from SAR to Sigma Delta for better accuracy and secondly would it is feasible design if I add an external MUX IC to I can use the same Sigma Delta for 10+ channels? This Pic MCU PIC24FJ64GC006 comes with sigma delta ADC with sampling rate of 244 to 62.5 Ksps. For single channel, I am ok with 6.4KHz sample rate per channel. Thanks

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  • \$\begingroup\$ The PICMZ series is their flagship with a 200 MHZ clock, 50 MHZ bus, etc, but MPU's with ADC's have resolution limits. Most all of the PIC series is 10 bits single ended input. In spite of cost and space, you will be much more satisfied with an external Sigma-Delta with 18 to 26 bits resolution and analog muxes to select channels. If possible use differential inputs in minimize in-band noise and DC drift. That's just my opinion... \$\endgroup\$ – Sparky256 May 5 '18 at 6:38
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    \$\begingroup\$ you can't mux sigma -delta but you can get 4 in 1 IC which can be cascaded with I2C \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 5 '18 at 11:02
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    \$\begingroup\$ Take note: it is better if you define the signal bandwidth (BW=0.35/risetime) then anti-alias filter, sample rate and what is the useful output? ( Peak, Avg, Peak/Avg ratio, RMS, Max/Min? and output interval of data then number of samples per output, averaged , your intolerance for error %) THEN decide what ADC you need. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 5 '18 at 11:10
  • \$\begingroup\$ There was a MicroChip power meter IC, with accuracy near 0.1% or better, that used sigma-delta for noise rejection. \$\endgroup\$ – analogsystemsrf May 6 '18 at 3:00
  • \$\begingroup\$ Incremental Sigma Delta can be used for multiplexing - sigma delta types used in audio for a continuous signal cannot be used for multiplexing. \$\endgroup\$ – sundar Oct 29 '18 at 21:35
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You might need a Incremental Sigma-Delta ADC for multiplexing. Because they have a reset cycle with each conversion.

I don't feel that ADC in http://ww1.microchip.com/downloads/en/DeviceDoc/30009312d.pdf is multiplexable upon checking this documentation.

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  • \$\begingroup\$ A so-called "incremental" sigma-delta ADC is the same as an ADC which has a "trigger" input to start a new sampling cycle, right? The ADS1178 has this and if not asserted used it will just continue sampling but I never knew that sigma delta converters with such a function had a name dedicated to them. \$\endgroup\$ – DKNguyen Oct 23 '19 at 19:23
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I'm not sure why no one brought up the STM32F373 with THREE 16bit Sigma-Delta that can do simultaneous conversions at 50Ksps single or multiplex them at 16.5Ksps(21 single ended channels or 11 differential channels), plus a 12bit 1Msps SAR ADC. ST has a App Note about using it for a power meter and they use the SDADCs for current and the SAR ADC for voltage. It has floating point + DSP at a 72Mhz. Plus 2 12bit 1Msps DACs, 2 RR analog comps, 15 timers, USB, CAN, etc. All the ADCs can be triggered from the same timer/source.

I'm using one to make a LCR/ESR meter. Right now I'm trying to see if I can use one of the DACs for the excitation voltage or have to go with an external DDS.

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  • \$\begingroup\$ Thanks a bunch. Will look at at for possible applications. \$\endgroup\$ – engineer May 19 '19 at 9:08

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