4.1 Semiconductions - Integrated Circuits (2) Flashcards
what is input offset current?
the difference between both input currents at an output potential of zero volts
how does input offset current occur?
as a result of asymmetry of the two input terminals
how is it possible to balance the asymmetry of the input stages?
by the means of offset voltage compensation
what is input bias current?
the median value of both of the input bias currents of the op
what is max voltage range?
the voltage range which destroys the amp when applied to either input terminals
max +/- 10v
what is the differential input voltage range?
the value of the difference between the two input voltages
max +/- 5v
in max voltage range, how can amps be protected from exceeding their limits?
protective circuits
how is an op prevented from excessive oscillation?
it is frequency compensated by using external or internal circuitry,
Influencing frequency response in order for it to remain stable
whilst decreasing its range
what two types of input impedances occur in the input stages of op amp?
differential mode impedance and
common-node impedance
where is output impedance effective?
at the output terminal of an op operating in an open loop mode
at what frequency is output impedance?
over 100 Htz
in the influence of supply voltage, what is the result of pole reversal?
destruction of the op
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?
capacitors are used to block the voltages of the power supply, directly from the op to ground
in the influence of supply voltage, what must be done if several ops are supplied with voltages from a common source?
important to block each and every op to keep individual amps from influencing each other
what is the closed loop voltage gain of a voltage follower circuit?
1/unity
what is a summing amplifier used for?
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
what is the name of the summing amp if the input resistors are all the same value?
unity gain inverting adder
what is the name of the summing amp if the input resistors are different values?
a scaling summing amplifier
what is an op amp comparator?
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
what type of feedback do op amp comparators use?
positive feedback or none at all
in op amp comparators, due to its high open loop gain, what does the op do?
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-
in op amp comparator, what is the output voltage totally dependant on?
the power supply voltage
in op amp comparator, what is used to set Vref? (4)
-resistive voltage divider
-battery source,
-zener diode or
-potentiometer (for variable)
what are op amps designed and optimised for?
used in closed-loop with negative feedback from its output to its inverting input
linear operation
what does high gain of a voltage comparator allow it to do?
operate non-linearly allowing for heavy saturation
a voltage comparator is optimised for continuous saturation, where is it always intended to be?
close to one supply rail or the other, not inbetween
what can voltage comparators convert?
convert linear input signals into digital output,
where are voltages comparators commonly used to connect?
connect two dissimilar electrical signals with a different supply voltage or reference voltage
in voltage comparator, if the output switch is HIGH, what occurs?
it creates a high impedance path meaning no current can flow
in voltage comparator, if the output switch is LOW, what occurs?
creates low impedance path to ground, through the pull-up resistor, with output being pulled to the lower power supply
in differential amplifiers, two input voltages are used to calculate and amplify the ‘difference’ of the voltages, what is the circuit sometimes known as?
subtractor circuit
in differential amplifiers, if the resistors are of equal value, what will the circuit become?
unity gain differential amplifier
in differential amplifiers, if the resistors are of equal value, what will the voltage gain of the amp be?
exactly 1 or unity
in differential amps, if V2 is higher than V1, what is the output voltage sum?
positive
in differential amps, if V1 is higher than V2, what is the output voltage sum?
negative
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?
Wheatstone bridge
if you were to change the resistive elements of a feedback amplifier with capacitive elements, what type of circuit would be created?
integrator amplifier
what does an integrator amplifier do?
causes the output to respond to changes in input voltage, and produces an output voltage proportional to the integral of the input voltage
how does an integrator amplifier work?
-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
what does the rate at which a capacitor charges depend on?
the value of the resistor or capacitor (RC time constant)
in an integrator amp, if you were to apply a square wave input, what would occur?
sawtooth wave output
due to capacitor charging and discharging
how are differentiator and integrator amp different?
the position of the capacitor and resistor has been reversed.
resistor forms part of negative feedback
what is a differentiator amp role?
produce a voltage output which is directly proportional to the input voltage’s rate of change with respect to time
how does a differentiator amp work?
-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
what is the disadvantages of differentiator amps?
-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
in differentiator amps, what are the resulting output signal waveforms from the following?
Square wave
triangular
sine
Square wave = spikes
triangular = rectangular
sine = cosine
how is control achieved?
by comparing the required output with a fixed voltage reference.
in control, what can a large loop gain achieve?
rapid detection of very small changes in output voltage
