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The Analog Front End: How Much Should Be Inside?

Analog front ends (AFEs) can range in frequency from Hertz to GHz. With regard to complexity, at one end of the scale we have an op amp with a filter. At the other end we have a full signal conditioning front end, intermediate analog signal processing, an ADC, perhaps a microcontroller unit (MCU), and sometimes even more functionality (which sort of defeats the definition of “analog front end”). AFEs will be the topic of the upcoming Integration Nation chat session. We will post the time for this chat in the next few days.

AFEs are great for designers because the devices give us quicker time to market. In addition, the high integration into a monolithic IC keeps internal components closer. This minimizes parasitics and IR losses. It also simplifies power supply bypassing.

There are specialized AFEs like the multi-channel AFE for digital X-ray detector, power-line communications AFEs, weigh scale/body composition AFEs, camera/camcorder front ends, AFEs for process control, heart rate monitor front ends, radar AFEs, energy measurement front ends, metering front ends, and smoke detector front ends — just to name a few.

To give a quick overview, here is a brief listing of some AFEs and their manufacturers.

  • ADI: AD73311, AD9920, AD7195, AD7730, ADAS1000, AD73360, AD73322
  • Exar: XRD98L59, XRD98L23, XRD9818, XRD98L59, XRD9827, XRD98L24, XRD9826, XRD98L25, XRD98L63, XRD9816, XRD98L61, XRD9836, XRD9824, XRD9827
  • Intersil: ISL51002, ISL98003, ISL98002, ISL51002
  • Maxim (the sponsor of this site): 73M1903, MAXQ3181, MAX5865, MAX19706, MAX19707, MAX19710, DS8005, MAX5864, MAX19700, MAX5866, MAX19705, MAX19708, MAX19713, MAXQ3183, MAX19700, 78M661x
  • Microchip: MCP3911, MCP3901, TC500, MCP3903, TC510
  • ST: E-STLC7550
  • TI: LMP90100, LMP91002, LMP90077, AFE030, LMP90078, ADS1191, LMP90079, LMP91000, LMP90080, LMP90097

I would like to highlight some very unique AFEs and comment on their analog integration content.

LM90100 sensor AFE 
(Source: Texas Instruments)

LM90100 sensor AFE
(Source: Texas Instruments)

First, there is the Texas Instruments LMP90100, a multi-channel, 24-bit sensor AFE that has continuous background calibration and sensor diagnostic routines. This AFE can interface with multiple types of sensors all at once. It can interface with RTDs, thermocouples, pressure sensors, load cells, and other voltage output sensors.

The way it does this is through an input mux, two matched current sources, sensor diagnostics, an embedded PGA with gains settable from 1 to 128V/V, and a 24-bit delta-sigma ADC. In my opinion, this is just the right amount of integration for a functional IC like this — any more and it might be overkill and any less would sacrifice needed functionality to quicken time to market for designers.

Another unique AFE series is the Maxim Integrated Teridian series embedded energy-measurement SoC (system on chip) family. The 78M661x family has a polyphase AC power measurement IC, single-phase AC power measurement IC, power distribution measurement IC, and an AC power monitoring IC. See Maxim Integrated’s website for more details and the 78M6610 review.

Octal Power and energy measurement SoC: 78M6618 
(Source: Maxim Integrated)

Octal Power and energy measurement SoC: 78M6618
(Source: Maxim Integrated)

The Maxim SoC takes eight single-phase AC outlets and measures the outputs of voltage and current sensors into a mux and into a delta-sigma converter. There is also a reference, battery and temperature monitors, and programmable FIR filter. In my opinion, the AFE ends at the ADC, but Maxim has been able to successfully add an MCU, display driver, and memory onboard so the device is actually classified as an energy measurement SoC.

So where do you think the line should be drawn in AFEs solutions? How much is too much as it relates to analog integration or just integration in general? Please give us your thoughts at our upcoming chat. Keep watching for the date and time.

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34 comments on “The Analog Front End: How Much Should Be Inside?

  1. BillWM
    October 1, 2013
  2. Steve Taranovich
    October 1, 2013

    @William Murray—nice article. Fortunately no one has figured out how to interface with the sensor digitally—that's still solely analog 🙂

  3. BillWM
    October 1, 2013

    Actually my Sr. Project in College used an Digital Acellerometer that I built myself —  (The position of the sensors magnet was measured via an array of digital output hall sensors)

  4. Davidled
    October 1, 2013

    78M6618 looks like Microcontroller as including Compute engine and Flash. I wonder if there is more information for power management.

  5. Steve Taranovich
    October 1, 2013

    @DaeJ—check out Maxim's extensive data sheet on their website—there is plenty of power management on board and details about how to use it efficiently

  6. Steve Taranovich
    October 1, 2013

    Hi Bill,

    Ah, the key phrase is “digital output”—the sensor part of the Hall effect device is a transducer that varies its output voltage in response to the magnetic field—still analog at that point

  7. Netcrawl
    October 2, 2013

    @Steve Yes I checked the site its great, Maxim claimed that it could lower battery management electronics costs by 35%, well its a pretty good stuff its double the accuracy of cell voltage readings. its a good improvement. 

  8. RedDerek
    October 2, 2013

    Now to just add some switched on the 8 power outputs and let the microcontroller handle the on/off control. If too much power is being consumed, the microcontroller can start turning off outputs.

  9. Davidled
    October 2, 2013

    There is a little bit explanation regarding on power management in datasheet. I expect that there is some flow chart or sequence related to interaction of other block inside chip. I would contact to tech support engineer in the Maxim.

  10. Steve Taranovich
    October 2, 2013

    @DaeJ—Maxim's 32 page data sheet explains it all in great technical details http://datasheets.maximintegrated.com/en/ds/78M6618.pdf

  11. samicksha
    October 3, 2013

    Yes maxim claims and counts this as one of the key feature, up to Eight Outlets Individually Measured by One IC.

  12. samicksha
    October 3, 2013

    Yes maxim claims and counts this as one of the key feature, up to Eight Outlets Individually Measured by One IC.

  13. eafpres
    October 4, 2013

    Hi Steve–great stuff.  Where I think these AFEs are REALLY helpful is in developing sensor packages, especially for a wirelessly connected remote sensor.  You can build one almost from off the shelf parts.  TI has some nice low power AFEs for those applications.

    I wondered why you didn't mention the 800 lb Gorilla of markets for AFEs–wireless handsets (i.e. cell phones/smart phones).  For nearly a decade there has been talk of AFEs making inroads into cell phone designs, with the attendant reduction in component count, reduction in cost, easier assembly etc.  If anyone ever really cracks that it will be big.  I wrote about a small piece that would help–a tunable capacitor.  Some of the big guns like MuRata have worked on integrated passives–IPDs which are a neighbor for AFEs.  Yet still there are 1.6B phones a year waiting for the perfect solution.

  14. Steve Taranovich
    October 4, 2013

    @eafpres—good point about cell phone AFEs—this will be a great topic to discuss on our next chat on October 16 at 11 AM East coast US time. We will be discussing the topic of “The Analog Front End (AFE): How much should be inside? “

     

    This IN blog will kick things off prior to the chat http://www.planetanalog.com/author.asp?section_id=3065&doc_id=561344&

     

    As usual, we are inviting an expert or two. Right now I am planning to have some consultants and designers that do analog designs on the call as experts. I will also invite ADI, Intersil, Microchip, STMicro, Exar and TI

  15. frederic_marvin
    October 15, 2013

    I couldn't agree more that adding too much of digital functionality to AFE doesn't really live up to the definition of analogue front-end. On a more practical side, with more functionality one gets the solution for dedicated application with less time and effort, which is undeniably important nowadays. Ultimately, this means that “functional” AFEs are for committed applications rather than any other. This raises the question what about those applications which are not covered by “functional” AFEs. Surely, AFEs applicable in such situations should be more flexible with preferably less functionality. Perhaps some analogue signal conditioning, an ADC and communication interface could be all one may need.  This post gives a nice representative of AFEs the market needs today, and I just feel to bring up to this discussion the AFEs with current input. In my opinion, they definitely have their place that often gets overlooked. From what I've seen recently, there're more applications which make use of light and the current input AFEs are interesting when interfacing with photosensors and perhaps other sensors too. Seeing that, we at Systemcom Ltd developed such flexible family of AFEs with current input. http://www.systemcom.hr/.

  16. Steve Taranovich
    October 15, 2013

    @frederic_marvin, please do join us tomorrow during our one hour chat online—your inputs are welcome!

  17. Steve Taranovich
    October 15, 2013

    @eafpres, please do join us tomorrow during our one hour chat online—your inputs are welcome!

  18. Steve Taranovich
    October 15, 2013

    @samicksha, please do join us tomorrow during our one hour chat online—your inputs are welcome!

  19. Steve Taranovich
    October 15, 2013

    @DaeJ, please do join us tomorrow during our one hour chat online—your inputs are welcome!

  20. Steve Taranovich
    October 15, 2013

    @RedDerek, please do join us tomorrow during our one hour chat online—your inputs are welcome!

  21. Steve Taranovich
    October 15, 2013

    @Netcrawl, please do join us tomorrow during our one hour chat online—your inputs are welcome!

  22. Steve Taranovich
    October 15, 2013

    @William Murray,

    please do join us tomorrow during our one hour chat online—your inputs are welcome!

  23. goafrit2
    October 16, 2013

    >> One can even make one's own custom ADC/AFE using an FPGA.

    I have seen the use of floating gate devices to make analog neural arrays. How these devices can perform when mass produced remains to be seen. FPGA may not be the optimal way to design ADC/AFE because of the noice the digital system will introduce in the ADC.

  24. goafrit2
    October 16, 2013

    >>  (The position of the sensors magnet was measured via an array of digital output hall sensors)

    That should be a long time ago. Now, MEMS can do the job more elegantly. 

  25. goafrit2
    October 16, 2013

    >  I would contact to tech support engineer in the Maxim.

    That is not necessarily a very good idea. If you have problems understanding the datasheet, the engineer will not help you. I have this rule of engagement, if a company fails to communicate clearly in its datasheet, they will fail to explain what the product means via emails. If you do not figure out the datasheet, try another product

  26. goafrit2
    October 16, 2013

    >> Yes maxim claims and counts this as one of the key feature, up to Eight Outlets Individually Measured by One IC

    Why is the word “claims” used for a measurement in a datasheet. It is either you believe it or not. I find it hard to understand why hard numbers could be disputed when competitors would have called that out. Sure they exaggerate on these datasheets within their test environment but most times they are right because they work in a competitive space.

  27. Davidled
    October 16, 2013

    That might be true, but in other case that I experienced while I have been working on project, tech support was one of beneficial components. Technical support line actually provided the detail explanation and also guided other reference to supplement the information. Personally, I got a lot of help from this tool.

  28. BillWM
    October 17, 2013

    Actually with the FPGA's lower core voltage, and ability to over sample,  noise performance is better than an MCU with ADC.

  29. fasmicro
    October 17, 2013

    >> Personally, I got a lot of help from this tool.

    But remember that you can get this support if your firm is buying a lot of units from the OEM. Usually in the electronics industry, no company will assign engineers to support a college student on his toy project. There are different levels of support depending on the volume you purchase. You can count on that if you are the big volumne customer but for others, it does not usually work. I cannot call Maxim to help me understand a datasheet easily when my project needs only ten units of the parts.

  30. Davidled
    October 18, 2013

    I wonder what a kind of role tech support engineer is. Datasheet is a summary of contexts. It does not mean that all essential information is described in detail. In the bottom line, this issue is case by case.

    So, based on only my experience, unfortunately, there is no doubt that project that I experienced in the past years got a huge benefit from tech line or support. I would like to encourage all engineer or student to use tech support line as much as you could to learn their experience and company product.

  31. yalanand
    October 27, 2013

    AFE hardware modules are used as to interface sensors of many sorts to digital systems, as long as hardware modularity. A radio frequency AFE is used in radio receivers, recognized as an RF front end. Atmel markets analog front-ends for smart meters. Analog Devices advertises a CN209 product for test measurement and test applications.

  32. SunitaT
    October 31, 2013

    FPGA may not be the optimal way to design ADC/AFE because of the noice the digital system will introduce in the ADC.

    @goafrit2, true. I dont think FPGA is the optimal way to design ADC/AFE. I think the best way to implement ADC/AFE is by designing custom made IC's.

  33. fasmicro
    November 6, 2013

    >> I think the best way to implement ADC/AFE is by designing custom made IC's.

    That is certainly a good point if you can make millions of ASICs. One of the key disadvantages in ASIC design is that you need volume to be profitable. If that is not the case, then MCU or FPGA becomes good options.

  34. fasmicro
    November 6, 2013

    From my own experience, you can get a lot of tech support if you are big firm putting lots of volume to partners. But when you are a hobbyst toiling in your garage, it makes things very difficult. Companies must look at volume as they allocate man-hours to support partners and customers.

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