{"id":1447,"date":"2010-07-07T11:15:50","date_gmt":"2010-07-07T15:15:50","guid":{"rendered":"https:\/\/wpmu2.mit.local\/?p=1447"},"modified":"2010-07-23T10:56:58","modified_gmt":"2010-07-23T14:56:58","slug":"a-low-voltage-ecg-analog-front-end-for-wearable-systems","status":"publish","type":"post","link":"https:\/\/wpmu2.mit.local\/a-low-voltage-ecg-analog-front-end-for-wearable-systems\/","title":{"rendered":"A Low-Voltage ECG Analog Front-End for Wearable Systems"},"content":{"rendered":"
\"Figure<\/a>

Figure 1: Block diagram of a typical wearable medical monitoring system.<\/p><\/div>\n

Advances in mobile electronics are fueling new possibilities for small, non-invasive, ambulatory medical monitoring systems that can be used to monitor a person\u2019s vital signs.\u00a0 These wearable devices are shifting the focus of healthcare from the hospital to the patient and their everyday life.\u00a0 In a typical system, shown in Figure 1, the sensor interface, analog-to-digital converter (ADC), digital signal processor (DSP), radio and\/or memory must all be powered from a small battery and fit in a small form factor.\u00a0 Given these constraints, the system complexity and energy consumption must be minimal.<\/p>\n

\"Figure<\/a>

Figure 2: A low-voltage, digitally-assisted AFE with on-chip ADC and DSP for wearable medical monitoring systems.<\/p><\/div>\n

This work focuses on a fully-integrated, low-voltage analog front-end (AFE) to be used for ambulatory monitoring of a patient\u2019s electrocardiogram (ECG).\u00a0 The design of such an interface is constrained by several considerations.\u00a0 First, ECG signals are on the order of 0.1\u20135mV in amplitude, residing in the 0.5\u2013100Hz frequency range, thereby requiring a low-noise AFE that can reject low-frequency flicker noise.\u00a0 Second, to reduce the number of required voltage regulators and hence the system complexity, the AFE should be able to operate from the same supply as the DSP, which can be less than 1V [1<\/a>]<\/sup>.\u00a0 Third, continuous ambulatory monitoring necessitates the use of dry electrodes to avoid using wet electrode gels, which may irritate the patient\u2019s skin if worn long-term.\u00a0 However, the high electrode impedance of dry electrodes requires amplifiers to have a very high input impedance to avoid signal attenuation.\u00a0 Moreover, the AFE must also be able to reject up to \u00b1300mV of electrode offset [2<\/a>]<\/sup>.\u00a0 Lastly, the AFE must be able to deal with 50\/60-Hz power-line interference (PLI), either through high common-mode rejection or notch filtering.<\/p>\n

We propose a digitally-assisted AFE with an on-chip ADC and DSP that can operate off sub-1V supply voltages as shown in Figure 2.\u00a0 The core of the AFE is a chopper-stabilized instrumentation amplifier (I-AMP) to mitigate flicker noise, similar to that found in [3<\/a>]<\/sup>.\u00a0 Electrode offset beyond the supply rails and high input-impedance are addressed by fully AC-coupling the inputs.\u00a0 Saturation in the front-end from PLI is avoided by using a mixed-signal feedback approach, in which PLI is filtered out digitally and fed-back in counter-phase at the input [4<\/a>]<\/sup>.\u00a0 This approach cancels interference right at the input, enabling power savings through voltage scaling.\u00a0 Lastly, good noise-efficiency is achieved by carefully partitioning bias currents, resulting in a micro-power ECG AFE.<\/p>\n

\r\nReferences
  1. J. Kwong, Y.K. Ramadass, N. Verma,<\/ins> and A.P. Chandrakasan, \u201cA 65 nm Sub-Vt<\/sub> Microcontroller With Integrated SRAM and Switched Capacitor DC-DC Converter,\u201d IEEE J. Solid-State Circuits<\/em>, vol. 44, no. 1, pp. 115-126, Jan. 2009. [↩<\/a>]<\/li>
  2. IEC International Standard, Medical electrical equipment \u2013 Part 2-47: Particular requirements for the safety, including essential performance, of ambulatory electrocardiographic systems,<\/em> International Electrotechnical Commission, 2010. [↩<\/a>]<\/li>
  3. N. Verma et al., \u201cA Micro-Power EEG Acquisition SoC With Integrated Feature Extraction Processor for a Chronic Seizure Detection System,\u201d IEEE J. Solid-State Circuits, <\/em>vol. 45, no. 4, pp. 804\u2013816, Apr. 2010. [↩<\/a>]<\/li>
  4. J.L. Bohorquez, M. Yip, A.P. Chandrakasan,<\/ins> and J.L. Dawson, \u201cA Digitally-Assisted Sensor Interface for Biomedical Applications,\u201d in Proc. IEEE Symposium on VLSI Circuits,<\/em> Honolulu, HI, Jun. 2010. [↩<\/a>]<\/li><\/ol><\/div>","protected":false},"excerpt":{"rendered":"

    Advances in mobile electronics are fueling new possibilities for small, non-invasive, ambulatory medical monitoring systems that can be used to…<\/p>\n<\/div>","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[26,27],"tags":[17,4151],"_links":{"self":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/1447"}],"collection":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/comments?post=1447"}],"version-history":[{"count":8,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/1447\/revisions"}],"predecessor-version":[{"id":1454,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/1447\/revisions\/1454"}],"wp:attachment":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/media?parent=1447"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/categories?post=1447"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/tags?post=1447"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}