Advertisement

Blog

Medical Device ASIC Integration: Optimize, Don’t Maximize

There are numerous posts on this site regarding the merits of analog ASICs for various markets, applications, and functions. Clearly, there are a lot of variables to consider before embarking on a mixed-signal ASIC development, and the decision should not be taken lightly. In my experience, implantable medical devices (IMDs) very commonly justify mixed-signal ASIC integration.

IMD products include pacemakers, defibrillators, neuro-stimulators, and drug infusion pumps. While the functions of these devices vary, they all typically have goals of size and power efficiency. Due to their implantable nature, it is desirable to make these devices as small as practical for patient comfort and mobility, and for ease of implant. Long battery life is also an imperative, since IMDs require explant surgery after their batteries are depleted. The combination of very strict size and power limitations often justifies mixed-signal ASIC integration for IMDs.

If we conclude that a mixed-signal ASIC is justified, we then have to decide on the extent of the integration. It is very tempting, and common, for IMD designers to reach the conclusion that they need to maximize integration in order to gain the size and power benefits of the customization and integration. A maximized integration is represented by a system-on-chip (SoC) ASIC. A typical SoC ASIC might include all required analog sensors and drivers, data converters, and power management. The SoC will also include control logic in the form of an embedded microcontroller unit (MCU) or a custom digital controller.

Many IMDs also include wireless communication to support communication to the IMD after implant. This is often an RF link using the medical implant communication service (MICS) band (~400MHz). Finally, the IMDs usually require some non-volatile memory (NVM) to store calibration constants, user settings, and diagnostic data. A true SOC would include all of these sub-systems in a single ASIC, and would result in the maximum level of integration. A resulting IMD could conceivably consist of nothing more than a battery, the ASIC, and some passive components.

Despite its obvious attraction, in my opinion, maximizing ASIC integration is rarely the best overall solution for IMDs. Here are a few ideas about what not to integrate for most IMD ASICs and why.

MCU: MCUs are incredibly versatile tools for IMD designs. They provide highly flexible platforms on which a wide range of systems can be built. MCUs typically include a wide range of peripheral functions, like oscillators, timers, communication interfaces, and data converters, and these peripherals are seamlessly integrated with each other on the MCU chip. The argument against a standard MCU and in favor of integration into the ASIC is that MCUs often contain far more features than are necessary for any given IMD.

If the primary goals are to minimize size and power, it seems obvious that we should identify the minimum set of required features and integrate them into a mixed-signal ASIC. However, there are some very attractive MCUs available that directly contradict that argument. These MCUs offer a range of low-power modes and are incredibly small (under 5mm2 ). With these impressive characteristics readily available in a relatively inexpensive standard MCU, it is difficult to justify the development time and cost required to integrate the equivalent MCU functions into a mixed-signal ASIC.

RF Communication: When RF communication is required, complete ASIC integration is difficult to justify. One reason is that, like MCUs, there are some attractive solutions readily available. These include standalone transceiver chips and MCU/transceiver combo chips.

Other arguments against RF integration are that the RF circuit design is complex and often requires a technology with specific RF capabilities. This limits the technology options for the ASIC and often conflicts with requirements of various ASIC functions. Finally, committing to the integration of the MICS communication locks the device designer in to that particular communication protocol indefinitely. Any future change to a communication protocol would thus require a new ASIC development.

NVM: Many available technologies support the integration of NVM into a mixed-signal ASIC, but, in my experience, it is rarely justified. The primary reason for this is simply that most MCUs include NVM. If we choose to include a standard MCU, we get NVM for free. In cases where we need more NVM than the MCU offers, we need to consider available options for standalone NVM chips, which include decent memory arrays (1 Mbit/s) in extremely small form factors (< 5mm2 ).

When defining an IMD device, it is important to keep our focus on optimizing rather than maximizing ASIC integration. While the technologies and tools are all available to accomplish the maximum integration level of a mixed-signal SoC, we need to strive to find the optimal solution. With that approach, I have found that ASICs for IMDs almost never include the MCU, RF, or NVM functions.

Tell us about your experiences with medical electronics and with ASICs or other customizable mixed-signal parts.

Related posts:

33 comments on “Medical Device ASIC Integration: Optimize, Don’t Maximize

  1. Dirceu
    July 23, 2013

      And also you can get an additional integration using SOCs that, besides the microcontroller, also has a section of low-power RF (eg CC430, nRF24E1, …).

  2. eafpres
    July 23, 2013

    @Andrew–a lot of good points in your article.  I was wondering about packaging as I was reading your article.  It seems to me that since, at a minium, you will have to encapsulate a battery, the device, and perhaps some sensor interface (like electrodes) then there isn't a big penalty from building a small system on a board, then packaging (encapsulating) that.  I don't think there will ever be a complete (i.e. including power, etc.) SoC off the shelf that meets all requirements and is implantable.  So you will always have a packaging process that you can leverage.

  3. Scott Elder
    July 23, 2013

    @Blaine – I think RCP fits that bill.  

    http://www.freescale.com/files/shared/doc/reports_presentations/RCPPRESENTATION.pdf

    RCP may even negate the need for a custom IC altogether.

    Medical ASICs are probably one of the best examples of an application for custom ICs.  I don't think there is a $10B market cap company that wants to risk medical liability for selling 100,000 pieces of a $2 part.  At least according to the deep-pockets clause written in the US constitution….don't recall the article though…but its there. 🙂

     

  4. BillWM
    July 23, 2013

    EKG, EEG, Ultrasound, CT, MRI, Blood Pressure, Pulse Oximeter, Glucose Test, are all area's where specialized IC's are done for better performance, at lower cost.

  5. TheMeasurementBlues
    July 23, 2013

    Medical devices often connect to computers and networks over Ethernet, USB, and RS-232, in addition to RF wireless.

    Medical Devices on the LAN

    Medical Devices Get Connected

    Medical Device Connectivity in the Home

     

  6. eafpres
    July 23, 2013

    @Scott–thanks, nice presentation at the link.  The stuff towards the end is very impressive, even integrating SMD parts embedded or on top of the final package.

  7. Davidled
    July 23, 2013

    As other aspects, not package of electronic

    Typically, when embedded or attached device to body, it makes sure that package does not bother the skin of body.  For example, pad type ECG/EEG device might be carefully reviewed.  Skin might begin to itch, when it attached for long period time. Pad package might be related to Electronic package type a little bit in terms of package type and design.

  8. Netcrawl
    July 24, 2013

    But most are connected via wireless networks, they can be mobile, able to move from one place to another, their connectivity depends on the cell site's signal strength.  

  9. eafpres
    July 24, 2013

    @Netcrawl–“But most are connected via wireless networks”

    This depends quite a lot on where you are talking about.  In my comments below on packaging, we were talking about embedded devices (i.e., like a pacemaker inserted into the patient's chest).  While some of those have wireless capability, it is very short range.

    Also, I was recently in an emergency room at a modern hospital for a day (not as a patient).  I noticed there was no wireless at all.  There was wired Ethernet in most areas.  The sensors all used cables back to the readout (i.e., the finger clamp pulse-Ox had a wire).  The infusion pump was not connected to anything.

    Now, for personal use, or home health care, some devices get wireless.  They may get a version of Bluetooth and connect to a smartphone that acts as a cellular gateway.  

    My view is that wireless in the professional/emergency side of health care is still evolving and wires are dominant.

  10. TheMeasurementBlues
    July 24, 2013

    @netcrawl,

    eafpres wrote “I noticed there was no wireless at all.  There was wired Ethernet in most areas.”

    If you read the blogs in the links I provided, you'll see that wireless is rarely used in hospitals. Several people, including eafpres, asked the author about wireless.

  11. BillWM
    July 24, 2013

    Hacking is one concern with Wireless or even net-connected wireline — this is why doctors very rarely these days put much in a medical report, MRI report, etc, that has any potential for external circulation inadvertently, or maliciously.

  12. Andy@Cactus
    July 24, 2013

    @Dirceu – These are the types of parts I was referring to when I mentioned MCU?Transceiver Combo chips.

    The two parts you mentioned in particular are very powerful & a great starting point for any IMD that needs RF for long-range communication.

  13. TheMeasurementBlues
    July 24, 2013

    @William, are you implying that we go back to paper records?

  14. Andy@Cactus
    July 24, 2013

    @Blaine – As you suggest, packaging is a huge piece of the puzzle for IMD integration (just not my direct expertise). There are several approaches to the packaging, and in general, better results require higher cost.  The battery is another significant piece of the puzzle.  For most traditional IMDs (Pacemakers, Defibrillators, Drug Pumps), the battery consumes more than half of the total device volume, and in some cases more like 80%.  Since the battery is such a big piece of the puzzle, we try to reduce it as much as possible.  This is typically done by employing very efficient power management schemes, which usually require customization.  So to your point, sometimes we integrate to reduce the size of the electronics, but more often, we integrate to save power, which in turn reduces the battery size.  There are also some new power source technologies that change the equation a bit for some applications.  I plan to post something on that topic in the future.

  15. Dirceu
    July 24, 2013

    @Andy: Thank you for the note,

         suppose I've not noticed your mention to the MCU / Transceiver integration.

         Also on the topic of integration (even you saying that the goal is not necessarily minimizing) Freescale just announced a Cortex-M0+ based microcontroller as the world's smallest ARM powered MCU, available in the ultra-small 1.9 mm x 2.0 mm wafer level chip-scale package, the KL02 CSP (RF not included).

  16. Andy@Cactus
    July 24, 2013

    @Dirceu – agreed – that K02 is very impressive.  There are a few others out there as well, that are less than 5 square-mm.  The ultra-small MCU is one of the keys to the extreme miniaturization we get on some of our newer-generation IMDs.  Our job is to find the best of what's already available, and customize to make it all play together.

  17. samicksha
    July 25, 2013

    Although i love using wi fi but i guess more than prone to hacking, wificannot be considered full proof specially for Medical Devices that to when we are talking about critical Medical situations,  wherein they need to be 24*7 connected also to add in wi fi you cannot be sure when your packet drops and connection trips.

  18. Scott Elder
    July 26, 2013

    @Andy

    I was wondering if it is possible to attach a MEMs energy harvesting sensor to a beating heart.  And if so, how much average power could one extract?

  19. Brad_Albing
    July 27, 2013

    @Scott – looks like we'll need to do some experiments.

  20. Andy@Cactus
    July 28, 2013

    @Scott- Energy harvesting, in general, is a hot topic for the medical device world.  To your idea specifically, I know of some work at U of Michigan, where they have developed a prototype of a self-powered pacemaker [http://www.gizmag.com/heart-powered-pacemaker/21329/]. I'm not aware of any mainstream devices using true energy harvesting as the primary supply, but there are lots of ideas under investigation.  The harvesting can apply to mechanical energy from heartbeat, respiration, walking, etc; body heat; body/cell chemistry; and of course outside sources like electromagnetic radiation. Since the power source is the largest physical piece of most IMDs, it makes sense to try to radically change the way we think about it.

  21. Brad_Albing
    July 29, 2013

    Hmm… now we need to design an electronic technique to eliminate itching.

  22. jkvasan
    July 29, 2013

    Andy,

    Energy harvesting, if deployed in IMDs, it would be great news for patients. Just to replace batteries, if one has to undergo surgery, it is a pity.

    Coming to packaging, it is more important to ensure that this packaging does not trigger the immunity system to think it is an alien. As discussed in my blogs 

    Need an Organ Transplant? Just Print It and Bioprinted Organs Save Lives efforts are on to make medical device implant packaging more bio-comaptible.

     

     

  23. jkvasan
    July 29, 2013

    “Tell us about your experiences with medical electronics and with ASICs or other customizable mixed-signal parts.”

    I have a pleasant experience using TI's ADS1298 chips. Measures 8 ECG leads with separate 24 bit ADCs for each channel. Extensively programmable through SPI port, this device has transformed the way ECG has been measured all along.

  24. Andy@Cactus
    July 29, 2013

    @Jayaraman – I agree, bio-compatibility is critical for any implantable device.  Traditionally, this is covered by encapsulating the electronics in some bio-compatible enclosure, so the ICs don't need to be concerned.  However, there is a constant push to change the enclosure approach for even more extreme miniaturization – so keeping an eye on bio-compatibility for all parts is a good idea.

  25. Andy@Cactus
    July 29, 2013

    @Jayaraman – I've been working with mixed-signal ASICs for abot 25 years & medical devices for about 22 years. Our company ( http://cactussemiconductor.com/ ) specializes in mixed-signal ASICs for medical devices.

    As you suggest, TI (and others) have some very useful parts for some of the more common medical device applications.  These parts offer a good compromise of performance, size, power, and cost.  For many projects, these standard parts are a great fit.  In other instances, a higher level of customization is required – either for feature set, performance, size, or power – and that's where an ASIC supplier steps in.

  26. Brad_Albing
    July 29, 2013

    @Andy – U of MI just showed up again in another blog I'm working on now. It'll be posted tomorrow on the Integration Nation site. Look for a blog with “wakeup radio” in the title.

  27. jkvasan
    July 30, 2013

    @Andy,

    Thanks for the link. Your programmable amplifiers are particularly interesting. You make ASICs on order or sell them to everyone?

  28. Andy@Cactus
    July 30, 2013

    @Jayaraman – We primarily develop full-custon ICs (for one customer/application), but have recently announced our first Application Specific Standard Product (ASSP) for Neuro-Stim applications.  That part was the subject of Brad's blog a few months back (http://www.planetanalog.com/author.asp?section_id=385&doc_id=559498).  The part and an evaluation kit will be available to the public very soon.  You can check our website for status or follow the links to obtain more information.

  29. jkvasan
    August 11, 2013

    Andy,

    That, is interesting. Nerurostim – is this chip targeting the physiotherapy segment or the ones used in cardiothoracic and cardiology side? You may also want to read my blog MCUs Can Kill Pain in People, which discusses the former application.

     

  30. Andy@Cactus
    August 12, 2013

    @Jayaraman – The primary application for the CSI021 ASSP is for implantable peripheral nerve stimulators.  These can be used to manage pain, as well as control various other body functions.  The device operation is quite similar to the TENS units that you reported on, but the range of stimulation currents is a little low for TENS.  These peripheral nerve stimulators are implantable, so the leads are attached inside the body, very close to the target nerve – so the stimulation amplitudes are typically lower.  The big design challenge for these devices is usually the aggressive miniaturization required for device placement near the target nerves, with minimally invasive implant surgery.

    While the device is intended for peripheral nerve stimulators, it is essentially a generic programmable current source, so it could prove to be useful in cardiac applications, as well as other non-medical applications.

  31. jkvasan
    August 12, 2013

    Andy,

    That was clear enough. I was just curious to know if the chip can be used in implantable pacemakers.

  32. yalanand
    November 30, 2013

    @Andrew, is it true that small  medical diagnostic devices like pill camera is using  RF for communication. If it is true then whether it will cause any side effects with the emitted radiation?

  33. Andy@Cactus
    December 2, 2013

    @yalanand,

    Most modern implantable medical devices include some sort of communication link between the impklanted device and an external programmer or controller.  Since the devices are typically completely enclosed in the body, this link needs to be wireless.  the wireless communication schemes typically fall in one of two categories.  The first is RF communication in the “Medical Implant Communication Service” (MICS) band, which is ~ 400MHz.  The second is Near-Field Magnetic Induction (NFMI), which uses magnetic induction waves, typically in the 100KHz-200KHz range.  My understanding is that, in both cases, the energy of the transmitted wireless signal is kept to a low enough level as to do no harm to the patient.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.