# Op Amps Flashcards

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

**signal power**

__transfer__**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**, the_{in}**closer**the value of**V**is to…?_{in} - This is the reason that in practice ___ ____ ____ is always required

- The
**larger**the value of**r**, the closer the value of_{in}**V**is to_{in}__V___{s} - This is the reason that in practice
is always required__high input impedance__

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 common-mode input signal -
**Infinite**bandwidth

An ideal **op-amp** 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 op-amps

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} = ?

G = ? = ? = ?

ß = ?

G is called the ____ ____and also the ____-____ ____ ____. It is almost entirely determined by the ____ ____ and is hardly affected by small changes in ___{_}

G is called the ** feedback fraction** and also the

**. It is almost entirely determined by the**

__closed-loop voltage gain__**and is hardly affected by small changes in**

__feedback circuit__

__A___{v}Op-amp input resistance = ?

In a feedback amplifier, the input resistance = ?

R_{in} = ? and = ?

R_{in} = V_{in} / i_{in} and

In feedback amplifier, V_{s} = ?

β < 1 ?

Feedback Fraction

The “closed-loop gain”, G, of this feedback system = ?

Feedback equation

Ohm’s law = ?

V =IR

KVL = ?

V_{4} - V_{1} - V_{2} - V_{3} = 0

KCL = ?

i_{1} +i_{3} - i_{1} - i_{4} = 0