By: Chenchen Qi Douglas Ciha John Hogan ECG Amplifier By: Chenchen Qi Douglas Ciha John Hogan
Considerations Preamplifier Filter Driven Right Leg Circuit
Preamp Specs Voltage range: 1.9 - 3.8 V Input signals: Allowed Gain: Middle voltage: 2.85 V 0.95V from center to each saturation point Input signals: DC offset voltage range: ±0.3 V Range of linear operations of input: ±5 mV Allowed Gain: 0.95/0.305 V = 3.115
Preamp Circuit G = 1 + 49.4k/RG Choose RG = 25 kΩ G = 3 Figure 1. LT1167 pin diagram [1]
Filter Observed ECG frequencies: Used 0.5 – 50Hz bandwidth Clinical Bandwidth: 0.05 – 100Hz Monitoring Bandwidth: 0.5 – 50Hz Used 0.5 – 50Hz bandwidth All that is needed to construct a monitor Naturally avoids 60Hz signal noise
Passive Band-pass Filter Figure 2. Band-pass fitter [2] We want fc,1 = 0.5 Hz and fc,2 = 50 Hz f0 = 1/ (2πRC) Choose R1 = R2 = 1 MΩ C1 = 3.18 nF C2 = 318 nF
Driven Right Leg Circuit Figure 3. Driven right leg circuit [3]
Driven Right Leg Circuit Patient not connected to ground Right leg connected to auxiliary amp output Connected through a buffer and two, 50kΩ resisters, for patient safety 50kΩ 50kΩ Figure 4. Right Leg Lead [4]
References [1]https://ay14- 15.moodle.wisc.edu/prod/pluginfile.php/75950/mod_res ource/content/1/LT1167%20instr%20amp.pdf [2]http://www.electronics-tutorials.ws/filter/filter_4.html [3]15.moodle.wisc.edu/prod/pluginfile.php/72917/mod_r esource/content/1/BME%20DSP%20textbook.pdf [4]https://ay14- 15.moodle.wisc.edu/prod/pluginfile.php/76349/mod_res ource/content/1/DRL-TexasInst-2011.pdf
Questions?