Sensors at University Of Durham | Flashcards & Summaries

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Lernmaterialien für Sensors an der University of Durham

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What are op amps?
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A differential amplifier, they produce a voltage in proportion to the difference of the voltages between the two inputs
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What is a voltage follower?
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A special case of a non-inverting op-amp, the gain is 1. It increases the current and so if useful when we either have a high input impedance or need a low output impedance
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What is the differential input impedance?
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The differential impedance is determined from the change in input current with a change in differential input voltage
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What is common mode impedance?
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It is between the terminal and ground and is determined from the change in bias current with common mode input voltage
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What is the common mode rejection ratio?
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It is a measure of the ability of an op-amp to reject common-mode signals (the signals the appear at both V+ and V-)
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What is the common mode gain and what is the differential gain?
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Common mode gain A(cm) magnifies the common mode DC voltage between the inputs. The differential gain A(ol) magnifies the difference between the two input voltages
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Why do we use negative feedback?
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Negative feedback controls the gain that the circuit provides through the use of resistors. We do this to provide stability, otherwise the op-amp would only be useful as a comparator 
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What is the consequence of op-amps being constructed of transistors?
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Transistors require bias current to make them operate as intended so some op-amp architecture requires small currents flowing into the op-amp to make them work correctly
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What is a comparator?
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It is an op-amp used to determine if a voltage exceeds a specific level
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What is a zero-level comparator?
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A comparator that works because it has a very high open loop gain so a small change in input voltage means that the amplifier saturates at either the maximum negative or positive voltage.  A zero level comparator is grounded so in reference to zero, however this can be changed to any V(ref)
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What is the problem with a zero level comparator?
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Noise makes the signal switch, even when the actual input signal is near zero
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Why do we need amplifiers?
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Because most passive sensors produce signals in the order of microvolts but digital systems require V and mV 
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Q:
What are op amps?
A:
A differential amplifier, they produce a voltage in proportion to the difference of the voltages between the two inputs
Q:
What is a voltage follower?
A:
A special case of a non-inverting op-amp, the gain is 1. It increases the current and so if useful when we either have a high input impedance or need a low output impedance
Q:
What is the differential input impedance?
A:
The differential impedance is determined from the change in input current with a change in differential input voltage
Q:
What is common mode impedance?
A:
It is between the terminal and ground and is determined from the change in bias current with common mode input voltage
Q:
What is the common mode rejection ratio?
A:
It is a measure of the ability of an op-amp to reject common-mode signals (the signals the appear at both V+ and V-)
Mehr Karteikarten anzeigen
Q:
What is the common mode gain and what is the differential gain?
A:
Common mode gain A(cm) magnifies the common mode DC voltage between the inputs. The differential gain A(ol) magnifies the difference between the two input voltages
Q:
Why do we use negative feedback?
A:
Negative feedback controls the gain that the circuit provides through the use of resistors. We do this to provide stability, otherwise the op-amp would only be useful as a comparator 
Q:
What is the consequence of op-amps being constructed of transistors?
A:
Transistors require bias current to make them operate as intended so some op-amp architecture requires small currents flowing into the op-amp to make them work correctly
Q:
What is a comparator?
A:
It is an op-amp used to determine if a voltage exceeds a specific level
Q:
What is a zero-level comparator?
A:
A comparator that works because it has a very high open loop gain so a small change in input voltage means that the amplifier saturates at either the maximum negative or positive voltage.  A zero level comparator is grounded so in reference to zero, however this can be changed to any V(ref)
Q:
What is the problem with a zero level comparator?
A:
Noise makes the signal switch, even when the actual input signal is near zero
Q:
Why do we need amplifiers?
A:
Because most passive sensors produce signals in the order of microvolts but digital systems require V and mV 
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