Q: ADAS1000 - Converting ECG raw data to voltage

Q: I am able to read raw data for my leads/electrodes, how do I convert this raw data to an ECG voltage? Firstly decide the operating mode. Here are 3 main operating modes on the ADAS1000: Analog Lead Mode, Digital Lead Mode and Electrode Modes. There are 3 Electrode Mode Configurations available depending on the application requirements. Analog Lead Mode: Digital Lead Mode: Electrode modes ( Single-ended input Electrode, Common Electrode A and Common Electrode B): Single-ended input Electrode: Common Electrode A: Common Electrode B: Write to the relevant bits in the FRMCTL, ECGCTL and CMREFCTL registers as described in the ADAS1000 datasheet to configure the mode. Write to the FRAMES register.This issues the read command to start putting the converted data out on the SDO pin. A: The received data will be left justified (MSB) irrespective of data rate. In electrode mode and analog lead mode, the digital result value is an unsigned integer. Electrode mode and Analog Lead Mode: Minimum value (000…) = 0 V Maximum value (1111….) = VREF/GAIN LSB = (2 × VREF/GAIN)/(2N– 1) ECG (voltage) = ECG Data × (2 × VREF/GAIN)/(2N– 1) where N = number of data bits: 16 for 128 kHz data rate or 24 for 2 kHz/16 kHz data rate. In digital lead/ mode, the value is a signed twos complement integer format and has a 2× range compared to electrode format because it can swing from +VREF to –VREF; therefore, the LSB size is doubled. Digital lead mode: Minimum value (1000…) = −(VREF/GAIN) Maximum value (0111….) = +VREF/GAIN LSB = (4 × VREF/GAIN)/(2N – 1) ECG (voltage) = ECG Data × (4 × VREF/GAIN)/(2N – 1) where N = number of data bits: 16 for 128 kHz data rate or 24 for 2 kHz/16 kHz data rate.

Q: ADAS1000 and Pace Detection

The ADAS1000 has a very flexible digital pace detection algorithm with a lot of programmability for various thresholds used in the pace detect algorithm. Please consult this in conjunction with the ADAS1000 datasheet. A good starting point for the pace thresholds is as follows: PACELVLTH =0x5C PACEAMPTH = 0x24 (default) PACEEDGTH = 0x0 (default) Note these settings may need to be tweaked for each application depending on what filtering is present in the ecg line up between patient and the pace algorithm. There are two componets to this, firstly the ADAS1000 pace channel has some filtering internally as there's a low pass 13kHz filter after the ADC, before it goes to the pace algorithm, so the ECG channel will introduce some rounding in the pace signal before the pace algorithm can digest it. The second area of filtering is external, between the patient and the ECG pin of the ADAS1000. As you design your system, assess what filtering you are placing in front of the ECG pins. Aggressive filtering in the line up from defib protection and ESIS (electro-surgical interference suppression) will change the shape of the signal at the ECG pins, so assess this first and choose bandwidths that allow the pace pulse through. To much filtering here might change the nature of the incoming pulse such that the pace algorithm can't detect as a valid pulse. If you find that some pace amplitudes or widths are not being detected, then one method to assess what's going on is to see what the pace pulse signal looks like as presented to the Pace algorithm. Either by probing at the ecg pins or alternatively, digitally by using the 128kHz data rate mode and capture a few seconds of data, take a look at how the pulse looks versus what you expected.

Q: ADAS1000 evaluation board and patient cables

Q : I've purchased an ADAS1000 evaluation board, the EVAL-ADAS1000SDZ and I need to know how to connect my patient simulator to the board? A: As documented in the User Guide, UG-426 , the ADAS1000 evaluation board uses a standard DB15 connector with the the following pinout Pin No. Mnemonic Description 1 V2 Analog input, Master ECG5_V2 2 V3 Analog input, Slave ECG2_V3 3 V4 Analog input, Slave ECG3_V4 4 V5 Analog input, Slave ECG4_V5 5 V6 Analog input, Slave ECG5_V6 6 SHIELD Output of shield driver 7 CE Common electrode, Master CM_IN 8 NC Not connected 9 RA Analog input, right arm, Master ECG3_RA 10 LA Analog input, left arm, Master ECG1_LA 11 LL Analog input, left leg, Master ECG2_LL 12 V1 Analog input, Master ECG4_V1 13 Spare Analog input, chest electrode or auxiliary bio-potential input 14 RLD Right leg drive, RLD_OUT 15 NC Not connected Make your own cable The actual component used on the board is a female DB1 5 component is a Tyco Electronics 1-1634585-2 or similar. The mating component would be a male DB15 plug, something like 5-747908-2 from TE Connectivity or similar Source a manufacturer standard patient cable with same pinout there are various manufacturers cables available from medical suppliers, you will need to review the pinout of the cable to ensure a match. when selecting an off the shelf cable, beaware of the impedance of the cable. If you intend to evaluate respiration, then the impedance of the cable should be kept <5kohms, ideally as low as possible.

Q: ADAS1000 - Example Calculations for each mode

The ADAS1000 contains different modes of operation, deciding which to use can be a bit confusing, here's a little guidance and also some example calculations in attached excel sheet (see below) Analog Lead mode use for typical ECG lead configuration, creates the analog lead up front before digitization in the ADC, generates LEAD I/II/III and the V wrt WCT has slightly lower noise performance than digital lead mode Preferred mode for normal ECG applications Digital Lead mode use for typical ECG lead configuration. Each channel is digitized by ADC and the lead is calculated after the ADC slightly higher noise performance than digital lead mode Electrode mode use where need to digitize each input individually and not interested in a lead measurement Each channel is digitized wrt VCM_REF Attachments: ADAS1000_RawData_to_Voltage_DifferentModes.xlsx

Question 1

ADAS1000 questions

Accepted Answer

Q 
 My questions to ADAS1000-4: a) Does ADAS1000-4 also work with only two electrodes e.g. LA and RL ? b) How does the respiration measurement (respiration-path) work and where do you have to connect the three outputs/inputs ? c) Does each ECG input channel an own high-pass filter? d) Can you configure/adjust the high-pass filter? e) What is the function of Shield Drive Amplifier? We want to connect the shields to GND. f) Could you send example source code written in C or C++ for ADAS1000-4? g) Can we provide a standard connection diagram? 
 
 A 
 a) The minimum number of electrodes required for ECG measurement would be 3, so 2 ECG electrodes, e.g. RA and LA and the RLD. This would give a one lead measurement. If RLD is not used, then the CMRR performance will degrade which will affect the quality of the ECG measurement. It really depends on what your customer is trying to do, the type of ECG instrument they are trying to develop. Note that an ECG measurement is always a pair of ECG electrodes, e.g. RA/LA&hellip;. Etc. b) The respiration measurement is made on a pair of electrodes (a lead). This pair of electrodes can be the ECG electrodes, e.g. LEAD I/II/III. Page 34 of the datasheet provides a detailed description but in summary a programmable high frequency differential current is driven out onto two electrodes and. The resulting impedance variation caused by breathing causes the differential voltage to vary at the respiration rate. The current is AC coupled onto the patient. There is a shallow modulation envelope that equates to the respiration frequency. RFI filtering, ESIS filtering in addition to the cable impedance will affect the ability to measure this small ohm variation in the presence of a large series resistance, Table 13 on the datasheet gives you the maximum allowable cable and thoracic loading. c) Low pass filtering is covered by the ADAS1000 (e.g. on chip 40Hz/150Hz/250Hz/450Hz) For HP (0.5Hz/0.05Hz) or Notch (50/60Hz) this would be something likely better done in the digital domain by yourself. d) See above. e) It is used to drive the shield of the ECG cables. It can be disabled if not used. f) There is in fact some ucontroller code available. This should provide some insight/starting point. Please take a look at https://wiki.analog.com/resources/tools-software/uc-drivers/renesas/adas1000 g) https://www.analog.com/static/imported-files/circuit_notes/CN0308.pdf In this circuit note there is a very useful connection diagram. It can be applied to the ADAS1000. Please also note that the evaluation board hardware is for use only for evaluation purposes, it was not designed to be connected to humans or animals. In terms of ADAS1000 configuration, it demonstrates the key elements in terms of decoupling and possible configuration for a 12-lead solution. However, please note it is not intended as a reference design. The component selection used on the evaluation board may not be suitable for end system use. The evaluation board schematic has not been tested against defib/esis signals. The end system design and component selection is the responsibility of the system integrator.

Question 2

ADAS1000 Drivers and Blackfin Framework

Accepted Answer

Q : I want to use your ADAS1000 in my ECG application and I need software drivers/starting point/sample code for interfacing to my ucontroller/DSP/ linux environment 
 A : On our WIKI webpage, we have 3 sets of drivers/frameworks to get you started with coding for the ADAS1000 
 ADAS1000 Microcontroller NO-OS Driver 
 The goal of this project (Microcontroller No- OS ) is to be able to provide reference projects for lower end processors, which can't run Linux, or aren't running a specific operating system, to help those customers using microcontrollers with ADI parts. Here you can find a generic driver for the ADAS1000 which can be used as a base for any microcontroller platform and also specific drivers for Renesas platforms. 
 https://wiki.analog.com/resources/tools-software/uc-drivers/renesas/adas1000 
 
 ADAS1000 and Linux Driver 
 Also available on our WIKI page is a linux driver for the ADAS1000. 
 https://wiki.analog.com/resources/tools-software/linux-drivers/iio-adc/adas1000 
 ADAS1000 and BF-527 Visual DSP framework 
 Visual DSP based code framework has been developed and is now available at the following WIKI location: 
 https://wiki.analog.com/resources/tools-software/bfin/adas1000 
 This code interfaces between the ADAS1000 and the ADSP-BF527 low power Blackfin Processor utilizing the SDP (System Demonstration Platform) with the ADAS1000 evaluation board.

Question 3

ADAS1000 ACLO Operation

Accepted Answer

Purpose : The ACLO block within the ADAS1000 is used to help user identify if an electrode has fallen off or if the connection is poor (higher impedance). This document captures some detail around the operation of the block and using it. 
 Implementation : Inject an AC current into each electrode and look for the signal in the digital data 
 
 A properly connected electrode will have a very small signal as the drive current flows into the Right Leg (RL). 
 A disconnected electrode will have a larger signal as determined by a capacitive voltage divider (source and cable capacitance) 
 
 Detailed description: 
 The circuit includes a DAC to drive the inphase/anti-phase sinusoidal signals at a fixed frequency of 2.039kHz. Each signal has a nominal peak-to-peak amplitude of 2V centered at +1.3V relative to the ADAS1000's AGND/DGND. 
 The ACLO circuit drives the 2.039kHz sinusoidal current into each electrode, it's a voltage DDS ac-coupled to each ECG pin. 
 The ECG channel is digitized through the ADC channel, this includes the ACLO content. Each channel is I/Q demodulated and amplitude detected. There's sqrt(sum-of-squares) processing to find the amplitude without having to worry about the phase shift of the received signal relative to the drive. The resulting amplitude is low-pass filtered and sent to the digital threshold detectors. The AC lead off detection occurs solely in the digital domain. If the resulting amplitude exceeds the programmed thresholds, a flag is asserted. The user also has the ability to read back the amplitude result from each channel. 
 Thresholds: 
 The thresholds are programmable (LOFFUTH &ndash; upper threshold) and (LOFFLTH &ndash; lower threshold). This pair of thresholds applies to all channels within the device. 
 The use of the upper threshold level should be clear - if the signal is bigger than some value, the impedance is "high" so a wire is probably off or the electrode contact is degrading. Some experimentation will be required to identify the appropriate threshold based on the particular cable/electrode/protection scheme as these parameters will typically be unique for the use case. This might take the form of starting with a high threshold and ratcheting it down until they tripped, then increase it by some safety margin. This would give simple dynamic thresholding that automatically compensates for many of the circuit variables. 
 The lower threshold was added for the case where the customer uses ACLO only, but for the event where an electrode cable has been off for a long time and the DC voltage has saturated to a rail, or maybe the electrode cable has somehow shorted to a supply. In either case there may be no AC signal at all, yet the electrode may not be connected. The lower threshold checks for some minimum signal level. 
 In addition to the AC Lead off flag, there is also a voltage measurement available on a per channel basis (LOAMxx registers). 
 ADC Out of Range: 
 There may be instances when using the ACLO function and using a common mode reference with one or more electrodes, where the lead off flag may not function properly. This situation may result in saturation of the input amplifiers and the ADC, resulting in the ADC outputting &ldquo;out of range data&rdquo; with no carrier to the leads off algorithm. The algorithm would then report little or no ac amplitude. The ADAS1000 contains flags to indicate if the ADC data is out of range &ndash; indicating a hard electrode off state. The ADC out of range flag is contained in the Header word (bit 20 in 0x40). 
 Things to note: 
 
 AC-lead-off results are based on ECG channel data which may be a differential measurement (Vector mode). 
 Channel Gain (x1.4, x2&hellip;.) and channel configuration (analog lead or not) have a direct effect on the ECG samples and therefore have a direct effect on the ac-lead-off results. Higher channel gains will result in higher codes in the ac-lead-off results. 
 When the contact impedance is low (ideal contact), the ac-lead-off current (whose carrier is at 2KHz) will result in a low voltage. When the contact impedance is high (poor quality), the ac-lead-off current will result in a high detectable voltage. 
 When an electrode is completely disconnected, the ecg input pin will float, depending on leakage currents, it may float towards the supply rail. In the event that it does float to the supply rail, the ECG channel will be saturated and the ACLO amplitude result would then return 0 or close to 0 - making it look like the electrode is actually connected. Therefore, in addition to monitoring the AC LO Flag, user should also monitor the ADC-OUT-OF-RANGE flags. The electrode should be considered as off when either the ADC is flagged as out of range or the ac-lead-off flag is set. 
 ESIS protection network and defibrillator protection networks load the circuit and have a direct effect on the sensitivity of the ac-lead-off circuit. 
 ACLO detection operates at 128kSPS data rate.

ACLO and Common Mode Configuration 
 
 One electrode with poor contact will have an effect on the ac-lead-off results of all the ECG channels it contributes to (directly or via RLD or via COM_IO)

In the example shown, the LL electrode is OFF, this has the following affect on the other leads

In this scenario, user should identify the electrode and remove from the RLD mix and COM_IO mix. This requires careful detection threshold setting and may even require a smart algorithm in the host to play a little bit with the RLD and COM_IO blocks before determining which electrode degraded or fell off. 
 
 Results from ADI Evaluation Board 
 Configuration: Measurements on RA electrode using ADI evaluation board. All other Channels were disabled. Measurements were made at the device pin - with no external filtering/cable included. 
 A programmable resistor was placed between the RA electrode and VCOM (1.3V). The ACLO amplitude measurement was recorded, the corresponding impedance calculated and plotted versus applied resistance. This plot is for Gain = 1.4. 
 
 adas1000-1 adas1000-3 ecg aclo ac-leadoff healthcare

Question 4

ADAS1000 FAQ Index

Accepted Answer

ADAS1000 FAQ Index 
 Evaluating the part 
 
 ADAS1000 evaluation board and patient cables 
 ADAS1000 - Converting ECG raw data to voltage 
 ADAS1000 and using a signal/function generator as the signal source 
 ADAS1000 - example calculations for each mode 
 
 Right Leg Drive 
 
 ADAS1000 Right Leg Drive function

AC Lead Off 
 AC Lead Off Operation 
 Pace Detection 
 
 It&rsquo;s all about pace 
 Using the pace algorithm - filtering, default values, understanding why you might not be detecting pace pulses. 
 
 Software 
 
 ADAS1000 Drivers and Blackfin Framework 
 
 Application Questions 
 
 ADAS1000 - can it be used in an EEG application? 
 ADAS1000 ECG - What are the advantages/disadvantages of DC coupled ECG system versus AC coupled? 
 ADAS1000 and DRDY 
 ADAS1000 and Crystal Oscillator

Question 5

The ADAS1000 device was designed as an ECG front end. Can I use it for EEG applications?

Accepted Answer

Q: The ADAS1000 device was designed as an ECG front end. Can I use it for EEG applications? 
 A: Firstly let's look at the differences between an ECG and an EEG signal: 
 ECG: 
 An ECG (electrocardiogram) is 'sensed' on the surface of the patient, on the skin typically using Ag/AgCl electrodes. These electrodes form an interface between the ionic flow of the heart and the surface electrode which basically receives the synchronized depolarization/repolarization of the heart on a beat by beat basis (Cardiac cycle). The ECG "electrodes" are placed in various positions on the patients chest,arms,legs capture these signals from the heart. The magnitude of these ECG signals is in the region of 100uV to 5mV. The ECG analog front end needs to be able to digitize these signals while rejecting the common mode signal that is also present due to AC mains and other environmental signals. As a result the CMRR of the system must be in excess of 105dB (where RLD or driven right leg is used). 
 For ECG applications, the various medical standards dictate the maximum input noise floor at 30uV pk-pk, which applies specifically to the instrument (system level). 
 EEG: 
 For EEG signals the electrode offsets can be almost as high and the input signal levels are on average at least 20 times lower meaning the noise floor must be on the order of 1-2 uV over a typical bandwidth of interest (0.1 to 80 Hz). 
 Summary 
 The ADAS1000 was designed for ECG applications, targeting noise performance that would support the required noise floor according to the various medical standards applied to the system level. The noise performance of the ADAS1000 is greater than that required by EEG applications, therefore the device is not suitable to be used directly as is in EEG applications. 
 However, with the application of external gain and removal of the DC offset component prior to the ADAS1000, it may be possible to use in some EEG applications.

Question 6

ADAS1000 Crystal Oscillator Startup

Accepted Answer

The ADAS1000 oscillator circuit requires total capacitance seen at the XTAL pins <20pF (ideally <15pF) to ensure reliable start up across operating conditions. 
 For some crystal oscillators, the pad footprint can be quite large and if the crystal is placed at a distance from the ADAS1000 device, then there can extra capacitance present at the XTAL pin that could cause issues with startup. 
 On the ADI evaluation board, the crystal used is a 8.192MHz crystal ECS-81.92-18-7SX-TR 
 
 Rm (ESR) = 100ohms max 
 C0 = 7pF max

Simulation configuration 
 
 Rm range 40 to 70ohms typical 
 Cparasitic = 4pF (board/pad/trace capacitance) 
 Variables in simulation = Temperature, C1 (crystal load), Co and ESR of crystal 
 
 The typical simulation plot below shows the crystal start up time over temperature for Co = 3pF and ESR = 40ohms. 
 C1 = 6pF (green) and 10pF (yellow). 
 The startup time increases with increasing temperature and with larger C1 as expected, but always starts up. 
 
 The following simulation plots Co = 5pF, ESR = 70ohms, C1 = 6pF (green) and 10pF(yellow) 
 It can be seen that the oscillator circuit takes longer to start up at higher temperature, but does always start up. 
 
 In your application, it is recommended to review the following: 
 
 Assess the crystal parameters, ESR and Co, choose a crystal with low ESR. Many manufacturers will provide test data showing typical crystal performance parameters. 
 Review your layout to assess the crystal location and footprint ensuring there is no addition of extra capacitance (total capacitance at the XTAL pin should be <20pF), measure the pin capacitance at the pad if necessary using a cap meter. 
 Use crystal load capacitor value from 5.6pF to 10pF 
 Using a smaller crystal capacitor value will have a pulling effect on the frequency. The frequency error should be <500ppm. 
 
 Example 
 If you suspect a crystal start up issue in your application (conversions not happening), then it is possible to try measure if the oscillator circuit is powering up. 
 Note: even if the crystal is not coming up, it is still possible to read/write the registers - so you should be able to confirm the power on default register settings of all registers. 
 Firstly you need to power the device up and enable it into operating mode (suggest writing 0xF804AE to the ECGCTL register (takes the device out of low power mode, enables the voltage reference). Take care not to connect a standard probe to the XTAL pins as this will load the circuit even more - use active probes. 
 If an active probe is not available, then write 0xF804BE to the ECGCTL register (takes the device out of low power mode, enables the voltage reference, enables into gang mode as a master which turns on the CLK_IO pin to bring the clock out onto the CLK_IO hardware line), now use a scope probe on the CLK_IO line to see if there is a 8.192MHz signal there. 
 Example of measurement on ADI evaluation board with C1=C2 =10pF

Question 7

ADAS1000 ECG - What are the advantages/disadvantages of DC coupled ECG system versus AC coupled?

Accepted Answer

Traditionally ECG applications have tended to be AC coupled systems, more recently DC coupled approaches are becoming more popular for various reasons. There are advantages and disadvantages to each approach which this FAQ will explain. 
 The main motivating factor for an AC coupled system is to remove the large DC component of the signal prior to the ADC. The offset itself depends on the type of electrodes used. For a typical stainless steel type electrode, this offset could be as much as +/-1V, while for AgAgCl electrodes, the offset will be within +/-300mV. 
 In a DC coupled system, the signal of interest rides directly on the DC electrode offset. While it does require a higher performance ADC, a DC coupled approach offers signification advantages; it offers greater flexibility, ensures fast restore of ECG to some event such as de-fibrillation pulse or surgical knife. 
 The ADAS1000 ECG Front end device is designed for applications requiring a single supply, DC coupled approach. The ADC used within the ADAS1000 is a oversampled SAR (19-bit at 2kHz data rate). 
 A quick summary is shown below, taking into account some key elements:

Parameter

AC Coupled

DC Coupled

ADC resolution

Lower ADC demands 12-16-bit

Higher ADC demands, requires 19-bit due to the DC offset

External components

Resistors/capacitors at the input, the capacitors become quite large for 0.05Hz HPF.

HPF can be easily done in digital domain

Fast restore *

Hardware fast restore techniques needed. E.g. circuit may switch out the large input capacitor

No issue, can restore the ECG signal very quickly, well within the required time frame

Front end gain 
 High-gain can be used prior to digitization 
 Only low-gain can be applied prior to digitization

* (to defib shock or electro-cautery, ablation). The instrument will n eed to restore the baseline quickly after the impulse so the physician can quickly see the return to QRS complex or otherwise

Question 8

ADAS1000 Right Leg Drive function

Accepted Answer

The right leg drive amplifier or reference amplifier within the ADAS1000 is used as part of a feedback loop to force the patient&rsquo;s common-mode voltage close to the internal 1.3 V reference level (VCM_REF) of the device. By using the RLD feature, it effectively centres the electrode input voltages relative to the input span, providing maximum input dynamic range. 
 A common question around the RLD function is related to what happens if I don't use the RLD ? 
 The significant benefit of the RLD feature is to improve CMRR performance, thereby rejecting noise and interference from external sources such as fluorescent lights or other patient-connected instruments, and absorbs the dc or ac lead-off currents injected on the ECG electrodes. 
 Take a look at the response of the ADAS1000 during ECG capture from a patient simulator. This shows a 3-lead configuration of Lead I/II/III. 
 As you can see, when the RLD is not connected, there is significant contribution of mains noise onto the ECG signal of interest. 
 With RLD connected: 
 
 Without RLD connected: 
 
 More about the RLD function itself: 
 Within the ADAS1000, the RLD amplifier can be used in a variety of ways. Looking at the block diagram below, the area within the thick black line encompasses what's inside the ADAS1000. A number of external passive components are used outside the ADAS1000 device to configure the gain. These are left external to ensure flexibility for the customer. 
 
 One of the components, Rin, is optional. It can be provided externally, alternatively, the internal 10k series resistors shown in each electrode path can be used as this "Rin" resistor (any combination of these switches, SW1 to SW6 can be closed) with the Rin resistance value changing depending on how many are closed. 
 The input of the RLD amplifier comes from the CM_OUT signal, either externally via the CM_OUT pin or internally. 
 The DC gain of the RLD amplifier is set by the ratio of the external RFB to the effective RIN value (internal or external). 
 The dynamics and stability of the RLD loop depend on the chosen DC gain and the resistance and capatiance of the patient cabling. Typically loop compensation using external component will be required. In some cases, lead or lag compensation may be required. 
 Patient protection resistor in the RLD path 
 Note that the RLD amplifiers short circuit current capability exceeds the acceptable current that can be driven onto a patient (set by the various medical standards). A patient protection resistor is required in series with the RLD_OUT pin to the patient cable to achieve compliance with the medical standards.

Question 9

ADAS1000 - Converting ECG raw data to voltage

Accepted Answer

Q: I am able to read raw data for my leads/electrodes, how do I convert this raw data to an ECG voltage? 
 
 Firstly decide the operating mode. Here are 3 main operating modes on the ADAS1000: Analog Lead Mode, Digital Lead Mode and Electrode Modes. There are 3 Electrode Mode Configurations available depending on the application requirements. 
 
 Analog Lead Mode: 
 
 Digital Lead Mode: 
 
 Electrode modes ( Single-ended input Electrode, Common Electrode A and Common Electrode B): 
 Single-ended input Electrode: 
 
 Common Electrode A: 
 
 Common Electrode B:

Write to the relevant bits in the FRMCTL, ECGCTL and CMREFCTL registers as described in the ADAS1000 datasheet to configure the mode. 
 Write to the FRAMES register.This issues the read command to start putting the converted data out on the SDO pin. 
 
 A: 
 
 The received data will be left justified (MSB) irrespective of data rate. 
 In electrode mode and analog lead mode, the digital result value is an unsigned integer. 
 Electrode mode and Analog Lead Mode: 
 
 Minimum value (000&hellip;) = 0 V 
 Maximum value (1111&hellip;.) = VREF/GAIN 
 LSB = (2 &times; VREF/GAIN)/(2N&ndash; 1) 
 ECG (voltage) = ECG Data &times; (2 &times; VREF/GAIN)/(2N&ndash; 1) 
 where N = number of data bits: 16 for 128 kHz data rate or 24 for 2 kHz/16 kHz data rate. 
 
 In digital lead/ mode, the value is a signed twos complement integer format and has a 2&times; range compared to electrode format because it can swing from +VREF to &ndash;VREF; therefore, the LSB size is doubled. 
 Digital lead mode: 
 
 Minimum value (1000&hellip;) = &minus;(VREF/GAIN) Maximum value (0111&hellip;.) = +VREF/GAIN 
 LSB = (4 &times; VREF/GAIN)/(2N &ndash; 1) ECG (voltage) = ECG Data &times; (4 &times; VREF/GAIN)/(2N &ndash; 1) 
 where N = number of data bits: 16 for 128 kHz data rate or 24 for 2 kHz/16 kHz data rate.

Question 10

ADAS1000 and using a signal/function generator as the signal source

Accepted Answer

Q: I'm evaluating the ADAS1000 and I don't have a patient simulator, how else might I evaluate the device? can I use a signal/function generator 
 A: As the EVAL-ADAS1000SDZ was designed for evaluation purposes and as such was not designed to be connected to a human or animal, the best methods for evaluation are to use either a patient simulator or a signal/function generator.Patient simulators are very convenient when evaluating the ADAS1000 as they have a myriad of features applicable for this application, some have respiration features and include pace maker artifacts. The Patient simulator we use during our demonstrations is generally the Fluke PS420. If you don't have a patient simulator, there are some things that you can do with a signal/function generator. 
 Here, we'll step through how you'd go about using the ADAS1000 evaluation board setup with the SDP board for USB-PC interface and a function generator. 
 
 Hardware

Power up the board using the +5V wall adaptor (provided as part of the EVAL-ADAS1000SDZ kit) 
 The LK links on the evaluation board should be in the default condition per UG-426 
 Connect the SDP board and USB cable 
 Connect the signal generator +ve terminal to one or more of the electrode inputs (RA/LA/LL/V1/V2) 
 Connect the signal generator to the RLD (or ground - this may depend on the generator) 
 Configure the signal generator for low frequency, small magnitude signals, ECG signals tend to be in region of a couple of mV and the frequency of interest will be low Hz.

Software
 
 launch the ADAS1000 evaluation board software from the Analog Devices folder 
 Starting at the main panel, click on the "default settings" button, this writes a few commands to power the device up into a particular mode. This mode is perfect when using a patient simulator, but some changes are necessary when using a function generator to ensure user can see the signals clearly. 
 The following changes should be made:

Clicking on the "Program all RW Reg", select the CMREFCTL tab. Here you need to re-configure the settings of the Common mode amplifier. The default software setting is (RA+LA+LL)/3 (Wilson Central Terminal) which is fine for normal operation and typically used in the V1 and V2 calculation However, if you are using a function generator with the same signal applied to all of the electrodes, then this won't be so useful and may confuse things. Therefore, change the LA/LL/RA to "No", this means the common mode is set to the internally generated 1.3V (VCM_REF) on chip. 
 Going back to the main panel now and select the "Stream ECG" button

Within the "ECG Update" tab, select "Electrode" Data Format. The signal below shows a 1Hz, 500mV signal from the signal generator 
 You may also need to change the "offset" within the "Graph Control" tab here 
 Changing the frequency of the signal generator to 10Hz, gives the following on all channels. Within the labview tools, it's possible to Right-Click and export the captured data straight out to excel for offline processing/analysis.

Question 11

ADAS1000 and Pace Detection

Accepted Answer

The ADAS1000 has a very flexible digital pace detection algorithm with a lot of programmability for various thresholds used in the pace detect algorithm. Please consult this in conjunction with the ADAS1000 datasheet. 
 A good starting point for the pace thresholds is as follows: 
 
 PACELVLTH =0x5C 
 PACEAMPTH = 0x24 (default) 
 PACEEDGTH = 0x0 (default) 
 
 Note these settings may need to be tweaked for each application depending on what filtering is present in the ecg line up between patient and the pace algorithm. There are two componets to this, firstly the ADAS1000 pace channel has some filtering internally as there's a low pass 13kHz filter after the ADC, before it goes to the pace algorithm, so the ECG channel will introduce some rounding in the pace signal before the pace algorithm can digest it. 
 The second area of filtering is external, between the patient and the ECG pin of the ADAS1000. As you design your system, assess what filtering you are placing in front of the ECG pins. Aggressive filtering in the line up from defib protection and ESIS (electro-surgical interference suppression) will change the shape of the signal at the ECG pins, so assess this first and choose bandwidths that allow the pace pulse through. To much filtering here might change the nature of the incoming pulse such that the pace algorithm can't detect as a valid pulse. 
 If you find that some pace amplitudes or widths are not being detected, then one method to assess what's going on is to see what the pace pulse signal looks like as presented to the Pace algorithm. Either by probing at the ecg pins or alternatively, digitally by using the 128kHz data rate mode and capture a few seconds of data, take a look at how the pulse looks versus what you expected.

Question 12

ADAS1000 evaluation board and patient cables

Accepted Answer

Q : I've purchased an ADAS1000 evaluation board, the EVAL-ADAS1000SDZ and I need to know how to connect my patient simulator to the board? 
 A: As documented in the User Guide, UG-426 , the ADAS1000 evaluation board uses a standard DB15 connector with the the following pinout

Pin No.

Mnemonic

Description

1

V2

Analog input, Master ECG5_V2

2

V3

Analog input, Slave ECG2_V3

3

V4

Analog input, Slave ECG3_V4

4

V5

Analog input, Slave ECG4_V5

5

V6

Analog input, Slave ECG5_V6

6

SHIELD

Output of shield driver

7

CE

Common electrode, Master CM_IN

8

NC

Not connected

9

RA

Analog input, right arm, Master ECG3_RA

10

LA

Analog input, left arm, Master ECG1_LA

11

LL

Analog input, left leg, Master ECG2_LL

12

V1

Analog input, Master ECG4_V1

13

Spare

Analog input, chest electrode or auxiliary bio-potential input

14

RLD

Right leg drive, RLD_OUT

15

NC

Not connected

Make your own cable
 
 The actual component used on the board is a female DB1 5 component is a Tyco Electronics 1-1634585-2 or similar. 
 The mating component would be a male DB15 plug, something like 5-747908-2 from TE Connectivity or similar

Source a manufacturer standard patient cable with same pinout
 
 there are various manufacturers cables available from medical suppliers, you will need to review the pinout of the cable to ensure a match. 
 when selecting an off the shelf cable, beaware of the impedance of the cable. If you intend to evaluate respiration, then the impedance of the cable should be kept <5kohms, ideally as low as possible.

Question 13

ADAS1000 - Example Calculations for each mode

Accepted Answer

The ADAS1000 contains different modes of operation, deciding which to use can be a bit confusing, here's a little guidance and also some example calculations in attached excel sheet (see below) 
 Analog Lead mode 
 
 use for typical ECG lead configuration, creates the analog lead up front before digitization in the ADC, generates LEAD I/II/III and the V wrt WCT 
 has slightly lower noise performance than digital lead mode 
 Preferred mode for normal ECG applications 
 
 Digital Lead mode 
 
 use for typical ECG lead configuration. Each channel is digitized by ADC and the lead is calculated after the ADC 
 slightly higher noise performance than digital lead mode 
 
 Electrode mode 
 
 use where need to digitize each input individually and not interested in a lead measurement 
 Each channel is digitized wrt VCM_REF

Attachments: 
 
 ADAS1000_RawData_to_Voltage_DifferentModes.xlsx

Question 14

ADAS1000 DRDYb operation

Accepted Answer

The purpose of this document is to describe a little more about the DRDYb operation of the ADAS1000. This should be read in conjunction with the ADAS1000 datasheet descriptions. 
 There are two modes of interfacing operation within the ADAS1000, 
 
 read/write registers (standard 32-bit register read/write operation) 
 Frame mode 
 
 Frame mode 
 
 Once the device has been configured and ecg conversions enabled, the host writes to the FRAME register to start reading ecg conversion data. The device is now in frame read mode, where the host issues all zeros on the SDI pin and reads the conversion results on the SDO.
 
 Any non-zero words on the SDI line during frame reads are understood to either be register reads/writes - where host wants to change the configuration or read some register information. As a result the frame read will be interrupted to allow the device process the incoming command.

The ADAS1000 performs data conversions and makes data available at the programmed rate (user programmable 2kHz, 16kHz or 128kHz). The DRDYb function signals data is ready for the host to read. 
 The DRDYb should be monitored as a level sensitive hardware pin, a software bit in the frame header or the level of the SDO. For simplicity, this article will focus on the hardware pin. 
 When the conversion data is ready, the DRDYb pin will be driven low by the ADAS1000, prompting the host to read the conversion result. 
 Once ecg conversions are started, new data will continue to be ready and available to read at the programmed rate, so DRDYb will keep going low to indicate ready status, it is now the job of the host micro to keep reading data at the programmed rate. 
 In the event that a frame is missed, not read completely or not read fast enough for the programmed rate, the DRDYb line will stay low - it stays low waiting for the frame register to be emptied (new results are only written into the frame register if it is empty). 
 The host should always check the level of DRDYb, if it is low, then the host reads a frame of data. If it appears to stay low, then the host should issue another full frame read. 
 The frame header will contain information on whether frames were missed. The frame header contains 2 bits which indicate if there has been an overflow since the last read (missed 1 to 3+ frames). These overflow bits indicate to the host that there has been a gap/break in the data stream. The data read at the time of a frame header with overflow bits set is valid data, it is the latest result.I 
 n the event that DRDYb does not return high, and the device is in frame mode, then the likelihood is a new set of conversion results arrived into the frame register at the same time as the previous read thereby keeping DRDYb low. The host should check again level of DRDYb, if it is still low, then issue clocks for another full frame read. 
 An example flowchart of configure to frame mode is shown below:

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ADAS1000: FAQ