tracking notch filter for electrocardiograph measurement

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2.2.2 Quality factor. The band width of band stop filter isdependent on quality factor and center frequency as equation[2]. The quality factor is of 8 by which input logic Q6-Q0 ofintegrated circuit band stop filter is 1111000.electrode on right hand, and GND1 is connected to electrodeon left leg.ALISO175+Isolation barrierf oQ = [2]BWRGVoutwhere Q is quality factor and BW bandwidth of band stopfilter.2.2. Frequency SynthesizerFunction of frequency synthesizer is multiplying inputfrequency, 40Hz to 70Hz, from noise frequency detector into6kHz to 10.5kHz as clock frequency for controlling switchedcapacitor.As mentioned, the multiplication ratio is then of 150times. Frequency synthesizer circuit consists of phase lockloop by which the minimum and maximum frequency ofvoltage control oscillator is as equation [3] and frequencydivider shown in Fig. 3.11fmin=and fmax=[3]R ( C + 32pF)R ( C + 32pF)R2Fnoi seC28330 pFR12 11 1CLK+ V cc25V.+Vcc2+V cc25V .5V.16 411 135 162 163O/ PLOAD RCO D/UEN Q0144PCAin1CLK Q15PCBin 312 MA X/CLK 14Q27C1BMIN 74LS191CD4518 6Q313PC2out+Vcc2P3 P2 P1 P06R6 R7 CTEN5V.C1ARES GND1M 100 K94 8 9 10 1 1512 VCOinR8 R9 R10 R117 8R2C2910 K 10K 10K 10 K2.2 uFGND211 MC14046R116 V.INH GND5 8Fig. 3. Frequency synthesizer.2.3. Noise Frequency DetectorInducing of electric field via signal cable is used to detectnoise frequency as input signal for voltage comparator.Hysteresis comparator shown in Fig. 4 is implemented asvoltage comparator by which ranging of transition voltage isassigned as equation [4]R2V = upper[ Vout(max)]R + R+R2and V = lower[ Vout(max)]R + R− [4]1 2VinR1Vout1 2ARVS1+ VS1- GND1 VS2+ VS2- GND2Fig. 5. Isolated instrument amplifier.3. Experiments and Results3.1. Band Stop FilterEach of the clock frequency of 7.5kHz, 8.25kHz and9.0kHz, respectively, is fed to band stop filter. Let input signalbe sinusoidal waveform, whose amplitude and frequency are of1Vp-p and of 10Hz to 100Hz. Output signals are measured andrecorded and the frequency response is then plotted as Fig. 6.From Fig. 6, that is, the clock frequency of 7.5kHz, 8.25kHzand 9.0kHz correspond with center frequency of 50Hz, 55Hzand 60Hz, respectively.Fig. 6. Frequency response of band-stop filter.3.2. Frequency SynthesizerAs mentioned, let the multiplication ratio be 150 times. Theinput signal frequency from noise frequency detector as theclock frequency ranging from 40Hz to 70Hz fed into frequencysynthesizer. The output signal frequency is measured andrelation between the input and output signal frequency isplotted as shown in Fig. 7 by which data1 means the data fromexperiment and data2 means the data from calculation. We seethat the relation between the input and output signal frequencyis linear enough.R2Fig. 4. Hysteresis comparator.2.4. Isolated Instrument AmplifierTo amplify ECG waveform having amplitude of 1mVapproximately, isolated instrument amplifier is applied andgain is of 1000 times. At here, we selected the integratedcircuit as ISO175 of Burr-Brown shown in Fig. 5. AL input isconnected to electrode on left hand, AR input is connected toFig. 7. Relation of input and output frequency.188
3.3. Filtering with Noise Frequency addedStandard ECG WaveformTo filter the noise frequency at each frequency, noisefrequency detector, frequency synthesizer, isolated instrumentamplifier and 4-order band stop filter are connected as thetracking notch filter. By using MATLAB program, thestandard ECG waveform [3], whose amplitude is of 1.2Vshown in Fig. 8, is created and added by noise signal. Thenoise added standard ECG waveform is conversed forBenchLink program in order to download onto arbitrarygenerator of HP33120A which generate real ECG signal shownin Fig. 9.(c)Fig. 10. Spectral from analyzing by using MATLAB.To confirm result in term of MSE, the standard ECGwaveform from Fig. 8 and the filtered ECG waveform fromFig. 9 which is recorded by WAVESTAR program, bothshown together in Fig. 11 by which dot line is the standardECG waveform and solid line is the filtered ECG wavform, areused to calculate MSE. The MSE is of 3.44%.Fig. 8. The standard ECG waveform [3].From Fig. 9, signal No. 3 is the standard ECG signalwhose amplitude is of 1V and period is of 1ms. Signal No.1 isthe noise added standard ECG signal by which amplitude andfrequency of noise is of 200mV and 50Hz, respectively. SignalNo.2 is the filtered ECG signal from the tracking notch filter.3 >1 >TTFig. 11. Comparison between Standard and Filtered ECG.For other experiment, let noise frequency be of 55Hz and60Hz. The experiment is performed the same as in case ofnoise frequency of 50Hz. Results of filtering noise frequencyof 55Hz show in Fig. 12 to 14. Fig. 13(b) shows that spectral ofthe filtered ECG signal at frequency of 55Hz is eliminatedwhen comparing with Fig. 13(a). The MSE is of 2.34%.2 >T1) Ch 1: 500 mV 250 ms2) Ch 2: 500 mV 250 ms3) Ref 1: 500 mV 250 msFig. 9. Real ECG waveform, upper: standard ECG [3]Middle: ECG combined with noise frequency of 50Hz.Lower: Filtered ECG.1 >2 >TTAlso we use WAVESTAR program to record the real ECGwaveform for analyzing spectral by using MATLAB program.Fig. 10 shows all spectral of real ECG signal correspondingwith signal shown in Fig. 9. From Fig. 10(c), see that spectralof the filtered ECG signal at frequency of 50Hz is eliminated.1) Ch 1: 500 mV 250 ms2) Ch 2: 500 mV 250 msFig. 12. Upper: ECG combined with noise frequency of 55Hz.Lower: Filtered ECG.(a)(b)(a)(b)Fig. 13. Spectral from analyzing by MATLAB.189
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tracking notch filter for electrocardiograph measurement

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