Digitisation

Question 1

How do binary numbers and decimal numbers differ?

Answer 1

• Decimal number = base 10, 10^x (10 possibilities)

- Binary = base 2, 2^x, 0 and 1 (2 possibilities)

Question 2

How do you calculate a decimal number from binary number?

Answer 2

101 = (1x4)+(0x2)+(1x1) = 5.

columns in 2

Question 3

How is a binary number created?

Answer 3

It is created by several low and high voltages using several bits.

Question 4

How do you calculate the maximum number encoded in a binary number of a given bit depth?

Answer 4

8 bits (28 = 256), 16 bits are used to encode physiological measurements.

Question 5

What is bit depth?

Answer 5

Bit depth = 2n.

Question 6

How is a digital signal measured from an analogue signal?

Answer 6

• Digital signal is measured from an analogue signal at each time point by an analogue to digital convertor.
• ADC takes analogue signal as input and outputs a binary number at each time interval corresponding to the signal.

Question 7

What is signal sampling?

Answer 7

amplitude of analogue signal is measured at equal time intervals and this is
converted into binary number.

Question 8

What is the resolution of the measured signal?

Answer 8

affected by the bit depth which needs to be high to accurately sample the waveform.

Question 9

What is the frequency of samples?

Answer 9

a good sampling frequency to represent signal accurately.

Question 10

How does a DAC work?

Answer 10

• Converts digital waves to analogue waves
• 8 bits is 8 resistors,
• the output voltage of the
  amplifier is the sum of all the voltages sent to the input
• a summing amplifier.

Question 11

What is voltage resolution and dynamic range? (VR)

Answer 11

Voltage resolution = size of the output voltage step

-VR = Vref/2bits.

Question 12

What is voltage resolution and dynamic range? (DR)

Answer 12

maximum possible voltage range obtained from the DAC, depends on Vref.

Question 13

How does an ADC work?

Answer 13

• Start received
• Control logic initialises the system
• Clock sends regular pulses to counter
• Counter outputs digital signal to DAC
• Staircase ramp generated to comparator
• Ramp Voltage rises and is closer to Vin
• Comparator shift states
• Signal to turn off the clock
• Digital output read
• Repeat

Question 14

Some limitations of ADC?

Answer 14

• Slow

- Analogue signal may be smaller than dynamic range so small changes may not be produced by DAC

Question 15

How can you increase ADC amplitude resolution?

Answer 15

Decrease the dynamic range by reducing Vref and increase bit depth.