AMPLIFIER CHARACTERISTICS AND FUNCTION REVISION QUESTIONS

Question 1

Does Amplification always mean making a signal bigger?

Answer 1

-no as you can get negative gain

Question 2

What is the term used for making a signal smaller?

Answer 2

-attenuation

Question 3

Key requirements of a biopotential amplifier?

Answer 3

• physiological processes being monitored can’t be influenced by the amplifier in any way
• Measured signal should not be distorted
• amplifier should provide best possible separation of signal and interferences
• amplifier has to offer protection of the patient from any hazard of electrical shock

Question 4

What is differential amplification?

Answer 4

• amplifies the difference in amplitude of the inputs
• positive output = positive deflection
• negative output = negative deflection

Question 5

What type of amplifier helps maintain integrity of the input signal (e.g output signal being as close as possible in amplitude to the input signal)?

Answer 5

• Buffer Amplifier

Question 6

How does that amplifier work?

Answer 6

• ensures output signal is the signal of interest and the same input
• output signal is measured against resistor
• input impedance is amplified greatly ensuring as much of the input signal is outputted
• input signal falls more on the bigger resistor so output signal is equal to input

Question 7

Define gain

Answer 7

• How much bigger/smaller the output signal is compared to input signal

Question 8

Unit of amplitude when gain is measured on a logarithmic scale?

Answer 8

-dB

Question 9

Vin = 2.3mV Vout = 4.6V what is the linear gain and what is gain in dB?

Answer 9

dB = Log10(Vout/Vin) X 20

LINEAR GAIN = VOUT/VIN

= 4.6V/0.0023V

= 2000

dB GAIN = Log(2000) x 20

= 66.02059991

=66dB

Question 10

If input changes to 3.5mV what is the new output?

Answer 10

• when a new input is introduced you just convert it into the same units as your linear gain (Volts in this case)
• so 3.5mV is 0.0035V
• Then you do
  0. 0035 x 2000 (og linear gain)

= 7 V