Analog Devices Integrated Analog Front-End Subsystem ADAS1000 Simplifies Design of Diagnostic-Grade ECG Applications

At the 2011 International Solid State Circuits Conference held in San Francisco not long ago, experts at the conference pointed out that Electronic technology will help promote the expansion of the medical care system from the hospital to the home, reduce related costs and improve people’s quality of life. , Battery The combination of technology and data acquisition techniques will be necessary to achieve such a transition.

Electrocardiography (ECG) devices have been witnessing such a shift as detection devices that play an extremely important role in modern medical applications and are widely used. When Willem Einthoven, the father of electrocardiography, invented the first real electrocardiogram device more than 100 years ago, it was huge and cumbersome, requiring many people to participate in the operation to realize an electrocardiogram detection. Today, high-performance 12-lead electrocardiographs can easily fit in your pocket.

Analog Devices recently launched the ADAS1000, the first product in a family of fully integrated AFE (analog front-end) chips that support monitoring-grade and diagnostic-grade performance in ECG systems. This information is output as a data frame, providing lead/vector or electrode data at a programmable data rate. The introduction of ADAS1000 continues the development trend of miniaturization and high performance of ECG equipment.

ADAS1000 makes ECG design so easy

Figure 1 is a simplified system functional block diagram of a single-lead ECG system for ECG design. If discrete devices are used to implement ECG design, in the analog front-end part, each lead needs to implement functional circuit modules such as protection circuit, buffering, amplification and filtering, and ADC in the figure. It would be a very challenging task for engineers to design this system independently: First, the selection of discrete components requires reference to numerous performance indicators, including filter sampling rate, bandwidth, noise, etc.; Ensure the consistency between channels; the matching between the front-end signal conditioning circuit and the ADC; numerous debugging points, the debugging workload is huge… In fact, in addition to the basic functional modules shown in the figure, the user’s design work may also Including: constructing RFI filters to reduce wireless interference such as mobile phones, broadcasting, etc.; selecting appropriate resistive devices to set appropriate filtering frequencies; adding electrostatic shields to sensitive devices to avoid ESD interference, so that products meet the requirements of relevant IEC standards.

Analog Devices Integrated Analog Front-End Subsystem ADAS1000 Simplifies Design of Diagnostic-Grade ECG Applications
ECG System Block Diagram (Single Lead)

Using ADAS1000 integrated analog front end, the above problems are effectively avoided! All front-end signal processing is implemented in a single chip, and what the user needs to complete is only to set the key registers through the data interface according to the system design requirements. The circuit design has become so simplified that only a few SMD resistors are needed, which can greatly shorten the design time of the ECG system, and the debugging points of the analog front-end part have also been reduced from dozens of discrete solutions in the past. Several, thus making system debugging very simple and speeding up the time-to-market.

The high level of integration enables the ADAS1000 ECG analog front-end signal chain bill of materials to be significantly reduced from as many as 50 devices to only a single-chip ADAS1000 plus a few discrete devices, which greatly simplifies the design of multi-electrode ECG systems. Figure 3 is the complete ADAS1000 evaluation board. The circuit in the red box is the multi-channel ECG analog front-end part. Two ADAS1000 chips are used in this circuit (to simplify the Display of test results, one of which is not patched) to realize multi-conductor Link extension. From the picture, you can see that the circuit is very clean (additional components and layout considerations have been added to the circuit for ease of testing).

Analog Devices Integrated Analog Front-End Subsystem ADAS1000 Simplifies Design of Diagnostic-Grade ECG Applications
ADAS1000 internal functional block diagram

ADAS1000 also supports seamless expansion of ECG. ADAS1000 solves the problem of consistency between channels very well. For the application requirements of more leads, you can flexibly use multiple ADAS1000s to easily expand the system. The high consistency makes the signal seem to come from the same chip. It hardly increases the development and debugging difficulty of the system.

Other key features and benefits of the ADAS1000 include: a DC-coupled channel scheme with simplified input switching, increased functionality, reduced power consumption, and unique post-processing benefits; 5 ECG electrodes measure only 19mW of operating power, which can easily disable any unused Channel or feature to enable minimum power consumption of only 11mW per lead; low noise performance (10 µV peak-to-peak from 0.05 Hz to 150 Hz) to support end equipment regulatory standards; different data frame rates available (2kHz, 16kHz, 128kHz) , which simplifies the task of data acquisition to the greatest extent; it can simplify the overall design, remove many discrete components, and reduce the overall size of the system, reduce power consumption, and shorten development time. The device also integrates pacemaker pulse detection and respiration measurement, features that are critical for high-performance ECG systems.

Development Evaluation Board Based on ADAS1000

High level of integration without sacrificing design flexibility

The advantage of high integration usually comes at the cost of lack of design flexibility. However, ADAS1000 allows designers to have more design flexibility to some extent, because users can use the SPI data interface to configure the registers to achieve correlation for any link. features, including filter bandwidth settings, data rate settings, sample rate settings, channel disable, and more.

ECG equipment has different requirements for different applications, such as portability, low power consumption, and low cost for home use, while clinics and hospitals have higher requirements for equipment features and performance. With the highly integrated ADAS1000 AFE, designers will be able to develop a new generation of ECG systems that are more compact and portable, while also delivering the diagnostic-grade accuracy needed to effectively analyze a patient’s heart condition. The device can be configured to optimize noise performance, power consumption or data rate for home, ambulance and clinical ECG systems.

Power consumption is the most important metric for portable ECGs. For a portable Holter monitor, usually patients need to carry it with them for a week or a few days to understand the beating law of the heart and truly judge the health of the heart. For this type of ECG market, it is generally necessary to ensure at least 8 to 10 hours of device battery life. From the perspective of the current lithium battery capacity, this is a challenge to the power consumption design of the system. The design engineer must A used device must impose a strict power budget. The ADAS1000 is designed with this in mind, maximizing the balance of power consumption and performance. To reduce power consumption, the user can easily disable any unused channel or feature when using the ADAS1000, turn off the signal acquisition channel, reduce the sampling rate, or use a different data frame rate, so that the lowest power consumption per lead can be reduced. to 11mW. In addition, the ADAS1000 incorporates a flexible power/noise adjustment option to reduce power consumption with appropriate noise tolerance, or reduce noise at the expense of increased power consumption, for specific applications.

Comprehensive technical support to help you easily implement system design

In parallel with the introduction of the ADAS1000 chip with an integrated analog front-end subsystem, ADI also offers a full-featured evaluation board for the ADAS1000 that includes the AFE, power supply, control and interface options to simplify development and manufacturing, and the ability to configure the AFE (from 5-lead to 12 leads) for final deployment. This set of demonstration evaluation system including full-featured evaluation board and evaluation software platform is a good tool for performance evaluation of ADAS1000 chip. The USB control software allows users to easily configure the chip and observe and analyze ECG signals and breathing signals; 5V on-board power supply, two ADP151s provide the power-on needs of ADAS1000; the optional R&C circuit on the CEG path makes the Users can flexibly adjust their filtering and cable modes according to system requirements. To simplify manufacturing test, development, and provide overall power-up testing, the ADAS1000 provides a set of DC and AC test stimuli, CRC redundancy testing, and readback capabilities for all relevant register address spaces via the CAL DAC.

ADI can provide ECG system designers with a full complement of components in addition to electrodes, including Blackfin® DSP (Digital Signal Processor), single-chip USB isolator ADuM4160, quad-channel digital isolator ADuM2401, 5kV DC/DC converter ADuM6000, transceiver ADF7023, linear regulators ADP150 and ADP151.

In addition to providing demonstration evaluation systems and supporting devices, ADI’s health care business unit specially established for medical Electronic applications brings together experts with rich experience in medical electronic application design, who can provide more targeted professional advice for ECG product system design, Solve design challenges.

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