mos cascode stage with p-channel current sourcethe folded cascode configuration figure 8.36 on page...

1

Figure 8.31on page 549

Cascode

P-channelCurrent Source

CS Gain Stage

Thévenin equivalent network:

MOS Cascode Stage with p-channel Current Source

Cascode Applications Lecture – EE330 – Dr. D. Estreich

November 8, 2017

From our last lecture slide set (Nov 6)

2

Raising the Resistance of a Current Source Using Cascode

CascodedCurrent Source

Figure 8.32on page 549

The resistance of Q4 can beRaised by cascading with Q3.

→ r04 raised to (gmr03)r04

3

Raising the Resistance Further By Use of Another Cascode Stage

Figure 8.33on page 550

1 0 0 1 2 02 01 3 03 04( ) ( )V m n p m m mA g R R g g r r g r r

What would AV be is all devices identical?

4

Example 8.5 on Page 551

Design the cascode stage of the circuit shown on the rightto provide a current of 100 microamperes (A) and simultaneouslyhave a an output resistance of 500 k. Using a 0.18 micron CMOSprocess, the parameters you have to work with are

Determine gate length L and length-to-width ratio (W/L) for bothtransistors and find the values of gate bias voltages VG3 and VG4.

2

'

1.8 volts; 90 μA/V

5 V/μm

Assume 0.3 V

DD p OX

A

OV

V C

V

V

Extra: You might also want to work Exercise D8.18 on page 552.

5

Distribution of Voltage Gain in CS Cascode Stage

Cascode

1 2 02 01

01 01 2

01

Obviously, ( )

Break gain into two parts: (2 stages)

V m m L

V V V

i

A g g r r R

v vA A A

v v

Figure 8.34on page 553

6

Distribution of Voltage Gain in CS Cascode Stage(continued)

Cascode

01 01 2

01

1 1 01 2 2

2 2 02

Starting with

1where and

V V V

i

LV m in in

m m

v vA A A

v v

RA g r R R

g g r

Where did this expression for Rin2 come from?

Answer: From slide #1 of Nov. 6th lecture (Ref. next slide)

7

Slide #1 from last lecture (on Monday Nov. 6th)

Figure 8.18on page 538

Figure 8.19on page 538

0

0

1

1 1

1

x m gs x L

x L Lin

x m gs m m gs m

v g v r i R

v r R RR

i g v g g v g

8

Cascode

01 2

02

01

2 2 02 22

01 01 02

1 01 21

1

2

Evaluate:

11 1

1

m

in

L

L

Lm m mm

m iV

m

n

r R

R

rRr

Rg g r gg

r r r

gg

r RAg

Distribution of Voltage Gain in CS Cascode Stage(continued)

9

The Overall Voltage Gain of the CS Cascode Stage

Cascode

1 2 02 01 2 02

2 02 01 012 02 01

2 02 0101

2 02

1 2 02 01

1 2

1

2

1

Evaluate:

Thus, V m L

V

V m m L m L

V V

V

m L Lm L L

Lm L

m

m m L

V V

A g g r r R if g r R

g r r R r Rg r r R R

Rg

A g R

AA A

A

r r Rr

g r

g g r r R

A A

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Common-Source Cascode Gain Stage Table

?

intrinsic

Table 8.1on page 554

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Let’s Go Further: Double Cascode Stages

And so on . . . .

Figure 8.35on page 555

We can continue to create ever higher resistances . . . But at what cost in parametertradeoff?

Cascode “2”

Cascode “3”

12

The Folded Cascode Configuration

Figure 8.36on page 556

13

Bipolar Transistor Cascode Configuration

The difference from the MOSFET is that we nowhave to include resistance r (now have r01||rinstead of r01).

Figure 8.37on page 557

14

Bipolar Cascode Amplifier With Cascode Current Mirror

Figure 8.38on page 558