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MCUs Are Increasingly Your Friend

IC manufacturers are packing more and more analog functionality into ICs. Surprisingly (to me, anyway), this analog integration is occurring with microcontrollers (MCUs), too.

One of my fellow editors, Michael Dunn, wrote a blog recently about something he called “extreme integration.” He was referring to FPGAs that might have up to 1000 pins. From the perspective of analog components, that does seem pretty extreme. But, of course, he's just talking about digital stuff, so it hardly matters.

But wait — from there, he talked about MCUs that had built-in analog functionality. Again, lots of pins — and quite a bit of analog stuff going on. At this point I realized that attention must be paid.

Michael was discussing an eval board from STMicroelectronics that he planned on procuring. Like many of these boards, there were various digital and analog inputs and outputs. So far, just another eval board. But even ignoring the extra op-amp and power supply circuitry on the board, the MCU itself was responsible for most of the analog I/O. Michael notes it had achieved an impressive level of integration.

From the manufacturer's data sheet, we note the following:

The devices offer up to four fast 12-bit ADCs (5Msps or mega-samples per second), up to seven comparators, up to four operational amplifiers, up to two DAC channels, a low-power RTC, up to five general-purpose 16-bit timers, one general-purpose 32-bit timer, and two timers dedicated to motor control. They also feature standard and advanced communication interfaces: up to two I2 Cs, up to three SPIs (two SPIs are with multiplexed full-duplex I2 Ss on STM32F303xB/STM32F303xC devices), three USARTs, up to two UARTs, CAN and USB. To achieve audio-class accuracy, the I2 S peripherals can be clocked via an external PLL.

Those four ADCs running at 5Msps and the two DACs running at 1Msps are not blindingly fast by any means, but it's plenty good enough for industrial data acquisition applications or some audio applications. The audio wouldn't be ultra hi-fi, but it would be acceptable for most applications.

The MCU device (just the IC, not the eval board) sells for about $5 in quantities of 100 pieces. If you were to build your own data acquisition system with four ADCs and just some of the analog parts cited above, you would spend more than $5 for the converters, a barebones MCU, op-amps, and sufficient PC board real estate to hold everything.

Just one more comment about the Eval board: The board has MEMS sensors to monitor acceleration along 3 axii and a compass/magnetometer. Now, if they can move that functionality into the MCU IC, then they will have achieved some amazing integration.

Have you used any of these MCUs that have all these features? How well did they work in your application?

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32 comments on “MCUs Are Increasingly Your Friend

  1. jkvasan
    July 29, 2013

    Brad,

    This device seems to be teriffic. It can suit medical applications such as pulse oximters and ECG recorders. The price is also reasonable for the features.

    I haven't used any ST chips but Silabs chips based on 8051 core. 8051F120 is still one of the most comprehensive devices suited for most applications. Another device would be RX62N from Renesas.

  2. Brad_Albing
    July 29, 2013

    @JK – And I am a complete rookie when it comes to using any microprocessor. But devices like this raise my awareness and interest.

  3. Brad_Albing
    July 29, 2013

    And your suggestions regarding usage in medical diagnostic or evaluative devices is spot-on.

  4. jkvasan
    July 29, 2013

    Brad,

    Performance and regulatory requirements for medical devices are becoming tougher by the day. MCUs like this have made medical devices better in measurement, processing, UI, connectivity and , on the whole, UX.

  5. Dirceu
    July 29, 2013

       Very good points about the so-called mixed-signal MCUs, which are particularly interesting in the field of instrumentation and control. By integrating various peripherals related to the analog world (op amp, comparator, PGA, transimpedance amplifier, ADC, DAC, …) are fit those applications where a high-end DSP would be overkill and expensive. Indeed, there is even the designation DSC (Digital Signal Controller) for some of them – to show some similarity with a DSP.

  6. antedeluvian2
    July 29, 2013

    I have used the Cypress PSoC1 for many years and its analog/digital integration allowed fro some very compact designs. I recently designed an “oscilloscope” that communicates with an Android tablet over Bluetooth. I used the PSoC5 and was very impressed. I only have voltage regulation, external signal overvoltage protection, and isolation circuitry outside of the micro. The rest is implemented within the PSOC5. I have 12 analog inputs through a multiplexer to two ADC converters (with programmable gain) so that two signals can be sampled simultaneously, the trigger circuitry, a thermocouple interface, 8 digital inputs, a D/A output, a PWM output with programmable freq and PWM settings plus some digital outputs. Also built in is the digital circuitry for DMA and UARTs and all the other digital goodies.

    The great thing is that it is all programmable through a UI that is really fun to use (althouh could use some refinement). The first trigger circuit I used had several problems. Ten minutes playing around with the schematic, reprogram and the problem was solved- no solder or wire. It is possible to bring out test points so you can see what any internal point is doing, analog or digital. If you want a real challenge you can actually manually route the connections to your desire if  you believe you can better the autorouter.

    There are tons of analog UI functions including  op-amps, comparators, PGAs, thermal component interfaces like RTDs/thermocouples and Thermistors. They even have IP that will allow the micro to automatically switch from a 4 wire RTD to a 3 wire to a 2 wire as the signal degrades as a result of broken wires.

     

    If you are interested in a slightly different presentation of the above project you can look at my entry on the “Create The Future” contest here.

  7. Brad_Albing
    July 29, 2013

    The regulatory issues are still there of course – you still need to go thru a lengthy certification process with any medical device. And if it has software or firmware, there are some very detailed Verification & Validation processes thru which you must do. Quite tedious of course. but necessary.

    I always use this test: Is the product safe enough — has it been tested thoroughly enough — that I would be comfortable having the device used on my Mom or on one of my children? If yes, then the testing was sufficient and done properly.

  8. Brad_Albing
    July 29, 2013

    @Dirceu – did not know of the “DSC” designation. I'll look for that now that I know of it.

  9. Brad_Albing
    July 29, 2013

    @before_the_flood – good info – thanks.

    And I'll take a look at the blog of yours that you cited.

    Pretty soon, maybe I can encourage you to write a blog or 2 for Planet Analog.

  10. Scott Elder
    July 29, 2013

    Brad and others….

    When I saw 4-12 bit ADCs at 5MSPS on one IC on a board for $11 I had to investigate.  The chip on DigiKey sells for about $4.50.  Which means the 12 bit ADCs are less than $1.10 each assuming all that other valuable stuff (2-12 bit DACs, CPU, memory) comes for free.  Since the cheapest 12-bit SAR ADC at 3MSPS on Digi-Key is about $2, I had to dive in a bit deeper.

    What I discovered is that the conversion rate can be as slow as 8us or so–125 KSPS.  And the guaranteed by design (not tested) linearity is closer to a 10-bit ADC.  And the specs are written in a non-standard way for data converters so its not clear what is really being provided here?  Which brings me to my point and question.

    I would like to hear from others regarding how they actually decide when to spend time and money investigating such a complex part.  Clearly one must have computed they needed 12 bits at some SPS rate to decide upon looking at this part.  But these parts are so sophisticated that I also wonder if anyone really does any checking that deep.  Is it that people read the 12 bits at 5 MSPS and build the system?  Measure the results and if it is good enough, the project is done?  In other words, is the marketing hype valuable and based  upon the premise that most engineers don't know if they need exactly 12 bits?  Or do most engineers do as I did, poor over the details when something sounds too good to be true?  It sure looks like lots of work to figure out what is really going on inside the ADC.  And a lot more work to build your circuit board only to find out its not really 12 bits.  

     I asked lots of questions, but really I'm just asking one:  Does marketing hype work when selling an analog IC to engineers who are trained to focus on numbers?

    Scott

  11. BillWM
    July 29, 2013

    I am working with an Eval-Board from AVNET  (LX-16 Board) that has a PSOC 3, and an FPGA right now.

     

    The PSOC on it does a number of things — it recharges and manages a battery, It has inputs for CAPSense capacitive push button switches, it Drives an LCD, and LED's, Does USB, and SPI I/O to reprogram the FPGA. and provides a 67 MHz system clock.  Quite versatile.

     

     

  12. BillWM
    July 29, 2013

    Infineon comes closest to a 12bit ADC in an MCU — All the others to date seem to really only be good for 10-11bits.  One however, if one can get by with a slower sample rate, add up 4 samples of 10 bit, and then interpret the output as 12bits.   This use of Oversampling to extend ADC precision was covered in an All-Programmable-Planet Blog by Steve Liebeson.

  13. jkvasan
    July 30, 2013

    @William,

    There are other devices which have 12 bit ADCs. Renesas RX62N, Silabs C8051. Renesas and Silabs offfer in-bilit 24 ADCs too.

  14. jkvasan
    July 30, 2013

    Scott,

    What an observation ! and thanks.

    I guess marketing hypes with flash banners may not just work. We are all used to reading the datasheets time and again to get the grip of the functionality.At the end of the day, it is not important if the chip is configured to process analog to a 12 bit data output but all other allied factors must be in tact to achieve this goal.

  15. Vishal Prajapati
    July 30, 2013

    Yes Sir, DSCs are available from Freescale and Microchip. Mostly they are optimised for Power Control, Motol Control and other high speed control loop capabilities. I have worked on Microchip dsPIC series. They have pretty good features for Arithmetic operations and they have good ADCs.

  16. Michael Dunn
    July 30, 2013

    You can hardly fault the chip by saying the converters are “closer to 10 bits”. Virtually all standalone converters are closer to n-1 (or n-2) bits  if you want to get picky. If you need true 12-bit performance, get a 14 or 16-bit part.

    Are you saying the real guaranteed conversion rate is 125kSa/s, not 5MSa/s?!? Where in the data sheet is that?

  17. Brad_Albing
    July 30, 2013

    @William – Looks like some pretty good analog functionality on the board. What is the price on the part?

  18. Brad_Albing
    July 30, 2013

    @VP – I need to look more closely at the product line from Microchip. Thanks for that information.

  19. BillWM
    July 30, 2013

    The PSOC 3 is about $ 3-4.   The dev kits range from under $50.00, to about $250 for the cadilac version.   The one with the FPGA, Battery, Ethernet, JTAG, LCD, etc was about 225 from Avnet.  

  20. Brad_Albing
    July 30, 2013

    Quite reasonable for either. Thanks.

  21. Dirceu
    July 30, 2013

       Some manufacturers promote its microcontrollers as being DSC. Examples are: LPC4300 from NXP,  DSPIC from Microchip and RX62N from Renesas. I think the AD converter capabilities and PWM resolution of the ATxmega (Atmel), could also qualify it for that denomination.

  22. Brad_Albing
    July 30, 2013

    I'll check out those devices. Thanks.

  23. SunitaT
    July 31, 2013

    Analog Devices Precision Analog Microcontrollers syndicate precision analog functions, such as high resolution ADCs and DACs, temperature sensor, voltage reference, and a host of other peripherals, with an industry-standard microcontroller and flash memory. The ADuC7xxx ARM7TDMI family incorporates 12-, 16- and 24-bit A/D converters, 12-bit DACs with flash, SRAM, and a host of digital peripherals designed for industrial, medical, instrumentation, communications, and automotive applications.

  24. Netcrawl
    July 31, 2013

    These areas (high speed DAC and ADC) are getting too much attention these days, it outspacing all other product categories in the electronic industry, what exactly driving this growth? As technology evolves and continues to advance, so too does the need to convert digital signals into analog. TI continues to gain inroad in this segment by developing data converters that are faster, low power and much higher resolution, they pushing the boundary of limits.   

  25. samicksha
    July 31, 2013

    Since processors are built to interpret and process digital data, they do it with the ADC, but DAC dosent sound common feature of processor.

  26. Brad Albing
    July 31, 2013

    @Sunita – Looks very interesting. Is it easy to set up and use?

  27. David Maciel Silva
    July 31, 2013

    Microcontrollers are making tasks interfacing with the world anaógico easiest, either in the form of signal processing (conditioning or treatment) as acquisition and communication speed / conversion.

    This is a tedência nowadays, we can find several articles with reliable sources and examples of source code ready to use …

    mbed is a very good example, watch the links below:

    http://mbed.org/prototype/

    http://mbed.org/media/uploads/robt/mbed_course_notes_-_analog_input_and_output.pdf

  28. Davidled
    August 2, 2013

    Silicon Provider provides OP-AMP, high resolution ADC and DAC, analog comparators and voltage reference with communication interface such as BT, Wi-Fi, ZigBee and USB. In some advanced package, power management and energy harvesting functionality are included.

  29. jkvasan
    August 6, 2013

    DaeJ,

    I understand that power management facilities are available with MCUs. I am not aware of energy harvesting functionality in any mcu. Can you provide some more details?

  30. Davidled
    August 6, 2013

    TI claims that MSP 430F5xx MCU of TI provides lowest power consumption for device with 25 MHz peak performance. These type MCUs has longer battery life with smaller battery for any consumer device. Also, TI comments that Battery in the MCU is not used for energy harvesting systems running off solar power. I think that power management system has some type configuration not to use battery of MCU.

  31. jkvasan
    August 12, 2013

    Scott,

    You caught the bull by its horn. Most times, one must read between lines if not words while going through a dataheet. Available resolution and realizable resolution are two different things and the distinction between the two gets clouded by the marketing hype.

  32. Victor Lorenzo
    November 27, 2013

    Yes, DACs are a very rare feature in SoC/MCU. Perhaps it is due to the fact that most closed loop control systems do not require feeding the process with analog stimulus from the MCU. Most temperature controller modules take digital inputs (ON/OFF, setpoint, etc) from the central controller, most motor drivers use servo-controllers that also take digital signals (Serial, Enet, CAN, etc), light controllers take also digital or PWM signals, BLess motors need no analog input control signal, and so on.

    Nevertheless, some Kinetis microcontrollers (and also others) do have analog outputs (DAC), but mainly for providing some audio feedback or alarms output.

    In the few automation projects I've worked so far we have not yet required analog output (not from the MCU) for process control.

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