FILTERS REVISION QUESTIONS AND ANSWERS

Question 1

Define ‘frequency response’ of an amplifier

Answer 1

• The frequency response of an amplifier refers to the band of frequencies or frequency range that the amplifier was designed to amplify.

Question 2

Draw a simple circuit to show components and configurations of a high pass filter and a low pass filter

Answer 2

• whiteboard

Question 3

Draw a frequency response curve for a filter used in ECG measurement

Answer 3

• label curve with the low frequency cut-off corner
• and high frequency cut-off (corner) points
• highlight bandwidth/bandpass of the filter and provide an explanation of what that part of the graph is representing

Question 4

Describe notch filters and how they work with reference to biopotential frequencies and why we avoid using them

Answer 4

• it filters out a frequency range e.g a 50Hz filter would filter 45Hz-55Hz
• consists of a high and low pass filter
• it applies these high/low pass filters at frequencies that sit in the middle of frequencies of interest
• it NOTCHES out signals occurring at that frequency
• BUT we avoid using them because it can notch out signals of interest so that’s why with ECG other measures taken such as relaxed patient and good skin to electrode contact

Question 5

What signals/waveforms that are not of interest might be picked up by our measurement system?

Answer 5

-noise/common mode noise

Question 6

If we are going to apply a filter to combat signals not of interest what frequency would the not filter be applied at (in UK)

Answer 6

-ASK Chloe