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4 Measurement of Biosignals and Analog Signal Processing

Signal Interference

1.

What forms of interference coupling of mains hum, where do these effects come

from and how can they be minimized?

2.

What type of shielding would be required to prevent capacitive or inductive coup-

ling of mains hum?

3.

Explain why the term 50 Hz noise is nonsensical.

4.

What physical quantities determine the magnitude of thermal noise?

5.

What is meant by white noise?

6.

Draw in a graph the course of a transient disturbance.

7.

What influence does the RC high-pass filter in the amplifier have on a transient

disturbance?

8.

What is the difference between the spectra of transient disturbances and noise?

9.

What is amplitude modulation and how is a demodulator for amplitude modu-

lated signals constructed?

Transducer for Non-Electrical Biosignals

1.

How is an electret microphone or a solid-borne sound microphone constructed?

2.

How does a semiconductor LED work? Why do semiconductor LEDs come in dif-

ferent colors? What does a typical emission spectrum of an LED look like?

3.

How does the emission spectrum of an LED differ from that of a laser?

4.

Which sensor can be used to detect light? How does it work?

5.

What type of sensor can be used to detect magnetic fields?

Interference Suppression and Analog Filtering

1.

What advantages do active filters have over passive filters and what disadvantage?

2.

Enter a 4th order active Butterworth high pass filter with cutoff frequency 160 Hz

into LTspice. Extend the high-pass filter to a band-pass filter with upper cut-off

frequency 1.6 kHz. Check the magnitude and phase frequency response.

3.

What is meant by group delay?

4.

How does a frequency dependence of the group delay affect the transmission of

signals?

5.

What is the principal difference between a selective filter, such as a power filter,

and a Bessel filter?

6.

What is the purpose of a frequency transformation?

7.

Which frequency transformation can be used to realize a 50 Hz mains hum filter

from a low-pass filter?

8.

Why is a Bessel filter often used when measuring an ECG?

9.

Please determine the pole and zero points and the transfer function of a normal-

ized 2nd order Butterworth low-pass filter and from this, determine the transfer

function of a 2nd order Butterworth high-pass filter by a suitable frequency trans-

formation, which has a cutoff frequency of 0.2 Hz with an attenuation of 3 dB.