Amplifiers

Question 1

3 main stages of Signal Processing?

Answer 1

Input = from a transducer, measurement converted into a voltage.

Signal processing = amplification of the signal, filtering, uses RC or logic circuits.

Output = digital output or analogue output.

Question 2

Define gain

Answer 2

Gain = if input units are the same as output units.

Gain in decibels = dB = 20log10(gain).

Question 3

Define Sensitivity

Answer 3

Sensitivity = if input units are not the same as output units.

Question 4

How does the 741-amp work to amplify signals?

Answer 4

• Inverting input voltage to a non-inverting input voltage and then output will be Inverted
• Open loop gain (100000) causes saturation of output voltage
• Amplifier supply voltage is converted into DC from AC mains supply

Question 5

How does negative feedback benefit application of the signal?

Answer 5

-Frequency response of amplifier must be linear ensuring isn’t distorted

(Vout directly proportional to Vin)

-Negative closed loop gain shows feedback signal goes through inverted input and is inverted with respect to output so gain is reduced

Question 6

Advantages of Negative feedback in signal amplification?

Answer 6

• Improved amplifier stability
• Reduced gain
• Amplifier output not saturated
• Increased bandwidth
• Increase in input impedance

Question 7

What is the difference between differential and simple amplifier?

Answer 7

• Differential signal at non-inverting input
• Both inputs have a difference which is amplified
• Vout/Vin = Vout/V2-V1 = R2/R1

Question 8

How is positive feedback useful in amplification?

Answer 8

• Output feedback to the non-inverting input
• Amplifier becomes permanently saturated
• used in oscillators and timing circuits

Question 9

What is it called when diodes/capacitors are used to convert AC to DC?

Answer 9

Rectification

• Diode allows current to flow in ONE DIRECTION only
• Capacitor is added to make output current steadier
• Zener diode used to fix the voltage

Question 10

Why is frequency response crucial in physiological measurement?

Answer 10

-Each frequency component of the signal should be amplified linearly

Question 11

Define bandwidth of an amplifier

Answer 11

Range of frequencies where the output amplitude is within 3dB of the maximum output 0dB

BW = fH -fL