Infinite Impulse Response Filter Design - Digital Signal Processing: Fundamentals and Applications - page 367

(a)

1

0

-1

0 0.5 1 1.5 2 2.5

(b)

1

0

-1

0 0.5 1 1.5 2 2.5

(c)

1

0

-1

0 0.5 1 1.5 2 2.5

Time (s ec . )

FIGURE 8.45

Results of ECG signal processing. (a) Initial corrupted ECG data; (b) ECG data enhanced by removing 60-Hz
interference; (c) ECG data with DC blocking and noise removal for heart rate detection.

where cur sign and pre sign are determined based on the current input xðnÞ , the past input xðn 1 Þ ,
and the threshold value, given as

if xðnÞthreshold cur sign ¼ 1 else cur sign ¼ 1

if xðn 1 Þthreshold pre sign ¼ 1 else pre sign ¼ 1

Figure 8.46 summarizes the algorithm.
After detecting the total number of zero crossings, the number of peaks will be half the number of
zero crossings. The heart rate in terms of pulses per minute can be determined by

zero crossing number
2

60
Number of enhanced ECG data
f s

Heart rate ¼

In our simulation, we have detected 6 zero-crossing points using 1,500 captured data points at
a sampling rate of 600 samples per second. Hence,