Tài liệu Circuits & Electronics P9 doc

„ Amp constructed using dependent source„ Superposition with dependent sources: one way tleave all dependent sources in;solve for one independent source at a time [section 3.5.1 of the t

„ Amp constructed using dependent source

„ Superposition with dependent sources:

one way tleave all dependent sources in;solve for one independent source at a

time [section 3.5.1 of the text]

„ Next, quick review of amp …

Review

Amp review

L D S

Key device Needed:

Let’s look at our old friend, the MOSFET …

i =

voltage controlledcurrent source

Key device Needed:

Our old friend, the MOSFET …

First, we sort of lied The on-state behavior of the

MOSFET is quite a bit more complex than either the ideal switch or the resistor model would have you believe.

D

S G

Saturation region

v

3 GS

v

+–DS

v

+–

v = −

Cutoff region

Saturation region

v

3 GS

v

+–DS

v

+–

v = −

Notice that MOSFET behaves like a current source

when

T GS

v ≥ −

MOSFET SCS Model

D

S G

When

the MOSFET is in its saturation region, and the

switch current source (SCS) model of the MOSFET is more accurate than the S or SR model

T GS

v ≥ −

Reconciling the models…

T GS

v ≥ −

T GS

v < − use SCS modeluse SR model

Note: alternatively (in more advanced courses)

or, use SU Model (Section 7.8 of A&L)

for fun! for digitaldesigns for analogdesigns

When to use each model in 6.002?

v

Saturation region

v

3 GS

v

T GS

v = −

Back to Amplifier

in saturationregion

To ensure the MOSFET operates as a VCCS,

we must operate it in its saturation region only To do so, we promise to adhere to the

“saturation discipline”

MOSFET Amplifier

in saturationregion

To ensure the MOSFET operates as a VCCS,

we must operate it in its saturation region only We promise to adhere to the

“saturation discipline.”

In other words, we will operate the amp

circuit such that

v GS ≥ V T and v DS ≥ v GS – V T at all times

v O ≥ v I – v T

Let’s analyze the circuit

First, replace the MOSFET with its

Let’s analyze the circuit

1 Analytical method: v O vs v I

(v O = v DS in our example)

2 Graphical method

:B

From A ( ) ,

2

2

T I

:

2 O DS

DS O

T I

O

v 2

K i

K

i

2 v

V v

L

0 L

S DS

R

v R

V

2 Graphical method

:B

Constraints and must be metA B

2

2

T I

S DS

R

v R

V

I

O vs v v

Large Signal Analysis

of Amplifier

(under “saturation discipline”)

1 v O versus v I

2 Valid input operating range and

valid output operating range

Large Signal Analysis

T I

v = −

2 What are valid operating ranges

under the saturation discipline?

S DS

R

v R

V

i = −

Large Signal Analysis

T I

O

T I

V v

2 What are valid operating ranges

under the saturation discipline?

S DS

R

v R

I

KR

V

KR V

Valid input range:

L

S

L T

KR

V

KR

V −1+ 1+ 2+

v I : V T to corresponding output range:

L

S L

KR

V KR

21

S

2

K V