4.1 Semiconductions - Integrated Circuits (2)

Question 1

what is input offset current?

Answer 1

the difference between both input currents at an output potential of zero volts

Question 2

how does input offset current occur?

Answer 2

as a result of asymmetry of the two input terminals

Question 3

how is it possible to balance the asymmetry of the input stages?

Answer 3

by the means of offset voltage compensation

Question 4

what is input bias current?

Answer 4

the median value of both of the input bias currents of the op

Question 5

what is max voltage range?

Answer 5

the voltage range which destroys the amp when applied to either input terminals

max +/- 10v

Question 6

what is the differential input voltage range?

Answer 6

the value of the difference between the two input voltages

max +/- 5v

Question 7

in max voltage range, how can amps be protected from exceeding their limits?

Answer 7

protective circuits

Question 8

how is an op prevented from excessive oscillation?

Answer 8

it is frequency compensated by using external or internal circuitry,
Influencing frequency response in order for it to remain stable
whilst decreasing its range

Question 9

what two types of input impedances occur in the input stages of op amp?

Answer 9

differential mode impedance and
common-node impedance

Question 10

where is output impedance effective?

Answer 10

at the output terminal of an op operating in an open loop mode

Question 11

at what frequency is output impedance?

Answer 11

over 100 Htz

Question 12

in the influence of supply voltage, what is the result of pole reversal?

Answer 12

destruction of the op

Question 13

in the influence of supply voltage, using a stabilised power supply has the tendency to vibrate at a frequency higher than the usual operating range of an op, what is done to compensate for this?

Answer 13

capacitors are used to block the voltages of the power supply, directly from the op to ground

Question 14

in the influence of supply voltage, what must be done if several ops are supplied with voltages from a common source?

Answer 14

important to block each and every op to keep individual amps from influencing each other

Question 15

what is the closed loop voltage gain of a voltage follower circuit?

Answer 15

1/unity

Question 16

what is a summing amplifier used for?

Answer 16

to combine the voltages present on two or more inputs into a signal output voltage.

output voltage is proportional to the sum of input voltages

Question 17

what is the name of the summing amp if the input resistors are all the same value?

Answer 17

unity gain inverting adder

Question 18

what is the name of the summing amp if the input resistors are different values?

Answer 18

a scaling summing amplifier

Question 19

what is an op amp comparator?

Answer 19

compares one analogue voltage with another analogue voltage level, or a preset reference voltage and produces an output signal based on the voltage comparison

compares the magnitude of the voltages and determines which is the largest

Question 20

what type of feedback do op amp comparators use?

Answer 20

positive feedback or none at all

Question 21

in op amp comparators, due to its high open loop gain, what does the op do?

Answer 21

it either swings fully positive or negative, on the application of varying input signal which passes some preset threshold

Vin greater than Vref then Vout= Vcc+
Vin Less than Vref then Vout = Vcc-

Question 22

in op amp comparator, what is the output voltage totally dependant on?

Answer 22

the power supply voltage

Question 23

in op amp comparator, what is used to set Vref? (4)

Answer 23

-resistive voltage divider
-battery source,
-zener diode or
-potentiometer (for variable)

Question 24

what are op amps designed and optimised for?

Answer 24

used in closed-loop with negative feedback from its output to its inverting input

linear operation

Question 25

what does high gain of a voltage comparator allow it to do?

Answer 25

operate non-linearly allowing for heavy saturation

Question 26

a voltage comparator is optimised for continuous saturation, where is it always intended to be?

Answer 26

close to one supply rail or the other, not inbetween

Question 27

what can voltage comparators convert?

Answer 27

convert linear input signals into digital output,

Question 28

where are voltages comparators commonly used to connect?

Answer 28

connect two dissimilar electrical signals with a different supply voltage or reference voltage

Question 29

in voltage comparator, if the output switch is HIGH, what occurs?

Answer 29

it creates a high impedance path meaning no current can flow

Question 30

in voltage comparator, if the output switch is LOW, what occurs?

Answer 30

creates low impedance path to ground, through the pull-up resistor, with output being pulled to the lower power supply

Question 31

in differential amplifiers, two input voltages are used to calculate and amplify the 'difference' of the voltages, what is the circuit sometimes known as?

Answer 31

subtractor circuit

Question 32

in differential amplifiers, if the resistors are of equal value, what will the circuit become?

Answer 32

unity gain differential amplifier

Question 33

in differential amplifiers, if the resistors are of equal value, what will the voltage gain of the amp be?

Answer 33

exactly 1 or unity

Question 34

in differential amps, if V2 is higher than V1, what is the output voltage sum?

Answer 34

positive

Question 35

in differential amps, if V1 is higher than V2, what is the output voltage sum?

Answer 35

negative

Question 36

in differential amps, what is the method called where the addition of extra resistors to the circuit in parallel are used, used to either add or subtract the applied voltages?

Answer 36

Wheatstone bridge

Question 37

if you were to change the resistive elements of a feedback amplifier with capacitive elements, what type of circuit would be created?

Answer 37

integrator amplifier

Question 38

what does an integrator amplifier do?

Answer 38

causes the output to respond to changes in input voltage, and produces an output voltage proportional to the integral of the input voltage

Question 39

how does an integrator amplifier work?

Answer 39

-uncharged capacitor acts like a short circuit allowing current to flow via a resistor. -capacitor begins to charge due to input voltage -negative feedback forces the op amp to produce an output voltage that maintains virtual earth at inverting input

Question 40

what does the rate at which a capacitor charges depend on?

Answer 40

the value of the resistor or capacitor (RC time constant)

Question 41

in an integrator amp, if you were to apply a square wave input, what would occur?

Answer 41

sawtooth wave output due to capacitor charging and discharging

Question 42

how are differentiator and integrator amp different?

Answer 42

the position of the capacitor and resistor has been reversed. resistor forms part of negative feedback

Question 43

what is a differentiator amp role?

Answer 43

produce a voltage output which is directly proportional to the input voltage's rate of change with respect to time

Question 44

how does a differentiator amp work?

Answer 44

-input signal applied to the capacitor. Dc blocked, AC allowed -frequency dependant low frequency = high reactance = low gain = low output voltage high frequency = low reactance = high gain = high output voltage

Question 45

what is the disadvantages of differentiator amps?

Answer 45

-becomes unstable due to oscillation at high frequencies (prevented by adding a small value capacitor across the feedback resistor) -capacitive input susceptible to random noise signals

Question 46

in differentiator amps, what are the resulting output signal waveforms from the following? Square wave triangular sine

Answer 46

Square wave = spikes triangular = rectangular sine = cosine

Question 47

how is control achieved?

Answer 47

by comparing the required output with a fixed voltage reference.

Question 48

in control, what can a large loop gain achieve?

Answer 48

rapid detection of very small changes in output voltage