SIGNAL DIGITISATION REVISION QUESTIONS AND ANSWERS

Question 1

Describe (using diagrams if helpful) what is meant by sampling on an analogue sample in the context of ADC

Answer 1

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Question 2

Describe effect of a sampling rate that is too slow/fast

Answer 2

• True signal is missed or removed

- If it is too high non-related signals are picked up (such as thoracic muscle potentials)

Question 3

What are the units for sampling rate and range?

Answer 3

• units for sampling rate are Hz (Hertz)

- units for range are V (Volts)

Question 4

What are they measuring and defining?

Answer 4

• Range is measuring the maximum amplitude measured e.g. +/- 10V (total range 20V
• sampling rate is the number of points of data acquisition per second e.g. 12 samples taken each second = 12Hz

Question 5

What is the Nyquist frequency?

Answer 5

• 2 x highest expected frequency

- it is essentially calculating the minimum sample rate

Question 6

When using a DAC (digital to analogue converter) with a range of +/-5V and 16-bit resolution what is the interval density?

Answer 6

5V/64000 = 78.13 µV

• so you do the range in volts divided by the amount of patterns
• to find out patterns it is just 2 to the power of however many bits and that’s the number you divide by with 16 bit they for some reason used 64000 patterns (not accurate but use this in exam)

Question 7

What two things impact the resolution of the digitised signal?

Answer 7

• number of intervals

- size of intervals

Question 8

Identify the limitations of signal digitisation and storage

Answer 8

• digitisation of analogue signal requires careful consideration of sampling rate, range and processor size ensure it is accurately measured/represented
• higher the resolution the nigger the digital space needed for storage (e.g. 16-bit vs 8-bit)
• if signal is filtered before digitised then it isn’t possible to get back the filtered components of the signal after digitisation