I am planning to build a wireless ECG sensor. This is my first attempt to do anything of this sort. I was wondering if i should go AC-coupled AFE or DC-coupled AFE? Which one would be easier?
Hi Win Naing:
The ADF7242 is a 2.4GHz transceiver IC that may fit your application well. The 8bit controller the ADF7242 features controls the basic low level functions required for wireless transmission and packet handling, relieving the user from those tasks and making the design of the wireless link really easy. Please note the user requires an additional microprocessor to configure RF parameters after power-up and load the data to transmit when available. This is done via a SPI port.
Lower in the frequency spectrum, the ADF7023 is a 862-928 MHz and 431-464 MHz frequency bands transceiver IC, with a similar arquitecture to the ADF7242. Very intuitive, very easy to use, it also features a low power 8bit controller. But it also requires a processor to control the rest of the system and execute the basic filtering needs your ECG AFE will likely require.
For a complete integrated system, please check the ADuCRF101. The ADuCRF101 is a cortex-M3 microcontroller embedded with a 862-928 MHz and 431-464 MHz frequency bands transceiver. It also features a 6 channel 14-bit adc. This is a full system in one package I recommend.
The AD8232 is a biopotential in / analog voltage out solution. The output stage is fast and powerful enough as to drive almost any block (amp, filter, adc, etc). When driving the next stage just keep in mind the output voltage ranges from ground to its positive supply.
The ADAS1000 family is comprised of digital-out parts and it works fine with any SPI-compatible microprocessor, dsp or fpga. Its IOVDD supply fixes the voltage levels of the digital interface.
Since they are battery operated, wireless applications require low power blocks and as a rule, AC-coupled front-ends feature lower power than DC-coupled solutions.
AC-coupled solutions remove the dc and near-dc frequency components, removing the large half-cell-potential. The signal of interest is later amplified with high gain so that a medium-low resolution ADC can digitize the biopotential.
DC-coupled solutions don´t remove the dc component, which now limits the gain of the amplifier. Since the tiny signal of interest has barely been amplified a high-resolution ADCis required to extract the bipotential signal. This high resolution adc comes with a power and area penalty.
The AD8232 is an ac-coupled single lead biopotential front end (link to product page). It is a perfect match for your needs (assuming you mean single lead / three electrode ECG solution). This part represents a flexible and very low power solution.
If you mean 3 lead (with 3, 4 or 5 electrodes) and minimizing power is a must in your system you could use several AD8232. You would just need to keep an eye on how the RLD is averaged and injected back to the body (if you decide to use a RLD).
Also, for multilead applications, if higher power can be afforded and ECG quality is the main design requirement (such as the quality required for diagnostics ECG equipment), I invite you to consider the ADAS1000 family of parts. These are DC-coupled, fully featured, fully configurable ECG AFE solutions, with optional respiration measurement and pace detection. Here you have a summary:
Let me know if this answers your question. Or you have further questions about the proposed.
Thank you very much Roberto, that helped!
For digital part I will require MCU and RF transceiver (for wirless transmission). I have been going through different ICs and found out that System on Chips like ADF7242 and CC2530(Texas Instrument) provide both RF transceiver and MCU on a single chip. So I wanted to know if analog device's chip (AD1000 or AD8232) are compatible with TI CC2530 chip? Secondly, since these SOCs (ADF7242 and CC2530) have MCU embedded I would not require an additional microcontroller (like ADuC7022), would I?
Is there any complete integrated system microcontroller embedded with 2.4GHz frequency Transceiver (Zigbee) in AD products?
I have decided upon using ADAS1000-3 with 3 electrode (single lead) for acquiring ECG signal from chest. How should i interface ADAS1000-3 with either ADuCRF101 or MCU with embedded 2.4G Hz transceiver (Analog device's product)?
Interfacing any of the members of the ADAS1000 family from a processor, dsp or fpga is quite straight forward since just a standard SPI interface is required. I invite you to download the ADAS1000 evaluation board use guide, available here:
where (in page 35 and following) you can find the detailed schematic of the reference design. Check pins 41 to 45 where the digital interface pins are located.
This reference design is for two ADAS1000 parts connected in gang mode (master and slave). Your design with a single ADAS1000-3 will be less crowded. The reference design uses a Blackfin DSP but using any other processor or fpga should be ok.
Page 46 of the ADAS1000-3 datasheet explains the primary SPI interface and output frame structure (page 51)
I wouldn´t it word the explanation better than that but let me know if anything is not clear or requires further explanation.
Regarding the wireless transceiver, the ADF7242 can provide the 2.4GHz link and can be easily controlled with minimal processing burden via a SPI interface with the same processor the system requires to control the ADAS1000-3.
Hello Win and Roberto,
Please note that the ADAS1000 evaluation board is not a complete reference design. The evalaution board identifies the necessary external components required around the ADAS1000, e.g. decoupling, oscillator, gain setting components for right leg drive etc. All of these components are necessary to support the ADAS1000 acheive functionality and performance in the end system.
The evalaution board is a vehicle to allow users become familiar with the ADAS1000 on a product level basis.
The evaluation board is not representative of an entire medical system, for example it does not contain the necessary patient protection or isolation that may be required from an end system.
The evaluation board has not been tested to medical standards.
When designing your system, please refer to the relevant standards that apply to your system and ensure that you include any requirements from that end.
Btw - there are drivers/example code available here that may be of use as you progress your desgin:
Thank you for the response. I am actually doing my final year project in university. So this is just going to be tested on me. I wanted to know what precautions or the protection circuit would be required before attaching the electrodes to ADAS1000? I read on some blogs that having large resistors grounded between the electrodes and input to ADAS1000 could serve as a protection circuit. Could you comment on that please?
While I have been supporting the ADAS1000 from an application point of view, I'm not familiar with all the precautions you will need to take at the system level, so I do urge you to carefully examine your circuit and the various standards to ensure that take the proper precautions.
One requirement that I recall is related to patient protection, the patient (and operator I believe) must be protected against dc currents in excess of 10uA rms in normal operation or under a (single) fault conditions (perhaps an overvoltage or surge or a fault somewhere in the system).
This comes directly from the various medical standards. I suggest you find the medical standard that applies to your system and work through it to understand what this directly means for you.
It's not clear to me exactly what information you gathered from the blogs you mentioned. I'm not sure having large resistors grounded between the electrodes and input to the ADAS1000 would serve as protection?
On the other hand, having large series resistors (sized appropriately) from the electrodes to the input of the ADAS1000 would serve to limit current out to the patient (as required by the standards) in the event of a fault on the ADAS1000 side of the resistor.
This article may be of interest to you in general.
Hi my name is miguel benalcazar, I am making my tesis, I have a question. Is necessary to use a master or directly I can to use ADAS1000-2BSTZ with a microcontroller?
ATT: Miguel Benalcazar
thanks for your message.
What is is that you are trying to do? How many leads are you trying to measure (and which).
From an electrical point of view, the ADAS1000-2 relies on signals from the master device (e.g. RLD for the system, the common mode signal, the conversion signal on SYNC_GANG). From a communications point of view the interfaces can be seperate, in that you can directly interface via the ucontroller to the ADAS1000-2.
If you can detail more on what you are doing, that will help give an appropriate answer.
I´m trying to connect ADAS1000-2 with controller and read the ecg signal but I don´t known as connect them. If there are some help that you can give me. the ucontroller is dsPic33fj128gp710 this has the four signals of SPI comunication, or, I need to connect others pines. Thanks for your help, that you have a nice day.
Att: Miguel Benalcázarmalky_benalcazar@hotmail.es
Because the ADAS1000-2 is designed to be operated as a "Slave" device, it's not ideal to use this standalone for ECG measurements - this is primarly as it doesn't have the RLD (right leg drive) amplifier.
I would advise that you look at using hte ADAS1000-1 instead.
In terms of your communications questions, the minimum
ADAS1000 DGND → ucontroller GND
ADAS1000 (SCLK) → ucontroller SCLK
ADAS1000 (CSB_0) → ucontroller CS
ADAS1000 (SDO_0) → ucontroller MISO
ADAS1000 (SDI_0) → ucontroller MOSI
you may also optionally use the DRDYb signal (output from ADAS1000) to ucontroller
you will also want to ensure that other digital siganls are handled appropriately at the ADAS1000 side e.g. RESETb, PDb, VREG_EN.
if you talk a look through the arrangement shown at the following page, that may help:
Thanks for your help, but I live in Ecuador and I try to buy adas1000-1 without response, I really. I want to know How can I to buy this dispositive here in Ecuador?
thanks for your help. Have a nice day
Att. Miguel Benalcazar
You will need to contact your local distributor or perhaps via a distributor like Digikey?
It's possible you may also be able to order small quantity samples directly via our website.
I can't help you further as I am focused on supporting technical questions.
Hope this helps..
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