eLFH - Operational Amplifiers and Electronic Circuits

Question 1

Function of operational amplifiers

Answer 1

Increase or gain an electrical signal by factor 10^6 or more in a linear fashion

Do not exhibit saturation at high voltage inputs or poor gain at low inputs

Question 2

Impedance of operational amplifiers

Answer 2

High input resistance (impedance) more than 10^6 Ohm

In order not to draw current from the upstream circuit

Question 3

Common mode rejection ratio (CMRR)

Answer 3

Operational amplifiers have inverting and non-inverting inputs in order to neutralise upstream circuit noise (i.e. add signals together and signals common to both inputs cancel out)

Therefore only voltage difference is amplified

This is called CMRR

Question 4

Features of operational amplifiers when combined with other elements in circuits

Answer 4

Usually have their output fed back into input

Result in modification of the gains of the amplifiers to perform different functions within a more extensive circuit

Question 5

Single vs differential inputs to operational amplifiers - explanation of CMRR

Answer 5

Single input can amplify mains ‘hum through capacitative coupling and therefore swamp the signal (e.g. ECG signal becomes swamped)

Differential input to op-amp allows noisy signals common to both inputs to cancel out and the smaller signal is amplified

Question 6

Analogue to digital conversion

Answer 6

Points on analogue sine wave are sampled at chosen frequency and digital value assigned to each sample

Forms a ‘staircase’ waveform

Question 7

Issue if sampling rate is too low in analogue to digital conversion

Answer 7

If sample rate is too low then will not be accurate representation of initial analogue signal