What is an amplifier?
An amplifier is a device used to increase the amplitude or power level of a small signal but without distorting it
Passive components ____ or ____ signal power
Active components ____ external power and ____
Passive components absorb or transfer signal power
Active components accept external power and amplify
Passive components __ ___ need power for them to work
Active components __ need power for them to work
Passive components do not need power for them to work
Active components do need power for them to work
For a voltage amplifier the Gain = ?
Gain = V_{out} / V_{in}
Gain is a ____ so has no ____
Gain is a ratio so has no units
To calculate the voltage delivered to the load we need to know the amplifiers parameters...(3 things)
 Input resistance of amplifier r_{in}
 Output resistance of amplifier r_{out}
 Open circuit voltage gain A_{v }
If we know the internal resistance of the source R_{s} , then the voltage across the input terminal of amplifier will be...(equation)
What is R_{s}?
The internal resistance of the source
R_{s} and r_{in} form a...?
Voltage divider
What does a voltage divider ciruit look like?
 The larger the value of r_{in}, the closer the value of V_{in} is to...?
 This is the reason that in practice ___ ____ ____ is always required
 The larger the value of r_{in}, the closer the value of V_{in} is to V_{s}
 This is the reason that in practice high input impedance is always required
What is the symbol for open circuit voltage gain and what is it larger than?
A_{v}  always larger than 1, very, very large!
What is Open circuit voltage gain?
It is the voltage gain if the amplifier is not loaded i.e. if R_{L} is replaced with an ∞ resistance
If a load is connected to the amplifier, the voltage across the load is...(equation)
A ____ output resistance is preferred in an amplifier
A small output resistance is preferred in an amplifier
What is IC and give an example
Intergrated circuit and an Op amp
Define inverting input
the phase angle of the output will be 180° different from that of the input applied at this terminal.
The ____ ____ is often omitted from circuit diagrams for simplicity, but it must be understood to be present at all times
The ground line is often omitted from circuit diagrams for simplicity, but it must be understood to be present at all times
A perfect amplifier should have...(5 things)
 High gain

High input impedance so that any signal could be supplied to it without a loading problem

Low output impedance so that the power supplied by the amplifier is not limited

Zero gain for commonmode input signal

Infinite bandwidth
An ideal opamp should have...(5 things)
• Infinite voltage gain, Av ≈∞
• Infinite input impedance, rin ≈∞
• Zero output impedance, rout ≈0
• Zero input offset voltage (i.e. exactly zero out if zero in)
• Infinite bandwidth
What is the current golden rule?
Because rin≈∞, virtually no current can flow into input
What is the voltage golden rule?
Because V_{out} ≈A_{v}(V_{p}V_{n}) and A_{v} ≈∞, V_{p}V_{n} ≈0, i.e. virtually no voltage difference between inputs
Comparison between ideal and real opamps
In a system, the ____ is compared with the desired ____
If there is a difference between the two, ____ is used to drive the output close to its intended value
In a system, the output is compared with the desired output
If there is a difference between the two, feedback is used to drive the output close to its intended value
V_{0} in a feedback amplifier = ?
V_{o }= A_{v} x V_{s}
If the feedback amplifier circuit is modified such that a fraction β of the output is fed back into the input, then the new output becomes;
V_{s} = ?
V'_{o} = ?
The new voltage gain Av ’ of the amplifier with feedback...(equation)
If ß A_{v}>>1, then A'_{v} = ?
What is ß?
The feedback fraction
Feedback voltage, V_{n} = ?