0.8V Bulk-Driven Variable Gain Amplifier

George Raikos and Spyridon VlassisElectronics Laboratory

Physics Department

University of Patrashttp://www.ellab.physics.upatras.gr

0.8V Bulk-Driven Variable Gain Amplifier

Introduction

Utilizes :Bulk-driven transistors low-voltage

operationMaster-slave technique control voltage

gain duplicate the gain

slope

Electronics Laboratory, Physics Dept.

ICECS 2010

Based on pseudo exponential approximation function (1+x)/(1-x)≈exp(2x) linear in dB gain.

Principle of operation

VP VN

M1

M1P M1N M4P M4N

M4

M2 M3

VG VG

MP

VDD

Vop

Von

2ID.B

1 : 1

1 : 1

2(ID.B-ID.T)

1 : 1

ID.B-ID.T

ID.B-ID.T

2(ID.B+ID.T)

2ID.B

1 : 2

VBID.B+ID.T

ID.B-ID.T

2 : 1 MP

D inputmb input m input

mb load m load D loadv

Igg I

gA

g

If ID-input=1+x and ID-load=1-x then :

exp( )vA x

Bulk transconductance of a MOS transistor is :

2 2mmb

F SB

g gV

Principle of operationWe seek to make:

1m input xg

1m load xg

exp(2 )mb input

mb loadv xg

Ag

1D input xI

1D load xI

exp( )vA x

Gain Control Circuit

Generates the appropriate currents for exponential circuit controls the VGA.

Based on master-slave technique.

(k)

MC1

MC1P MC1N

MC2 MC4 MC5MC3

MC6 MC7

IT C

VDD

VG

VCM -(½)VR

IR

MS2VFb

MS1

MS1P MS1N

VG

VCM +(½)VR

Slave differ.pair

IB

ID.B+ID.T ID.B+ID.T

ID.B+ID.T

Master differ.pair

Electronics Laboratory, Physics Dept.

ICECS 2010

Gain Control Circuit

(k)

MC1

MC1P MC1N

MC2 MC4 MC5MC3

MC6 MC7

IT C

VDD

VG

VCM -(½)VR

IR

MS2VFb

MS1

MS1P MS1N

VG

VCM +(½)VR

Slave differ.pair

IB

ID.B+ID.T ID.B+ID.T

ID.B+ID.T

Master differ.pair

Electronics Laboratory, Physics Dept.

ICECS 2010

VFb the feedback voltage Thus, IR=IB+IT

IR=gmb1VR VCM :Common mode

voltage

VR relatively small (50mV)

Gain Control Circuit

The input transconductance is equal to:

(k)

MC1

MC1P MC1N

MC2 MC4 MC5MC3

MC6 MC7

IT C

VDD

VG

VCM -(½)VR

IR

MS2VFb

MS1

MS1P MS1N

VG

VCM +(½)VR

Slave differ.pair

IB

ID.B+ID.T ID.B+ID.T

ID.B+ID.T

Master differ.pair

Electronics Laboratory, Physics Dept.

ICECS 2010

The slave pair obtain equal transconductance with master pair.

gmb-

input≈(IB+IT)/VR

Linear dependence from tuning current Process independence

gmb-

input,slave≈(IB+IT)/V

R

Variable Gain Amplifier

Bulk-driven differential pair with bulk diode-connectedloads

VP VN

M1

M1P M1N M4P M4N

M4

M4R

ID.B+ID.TID.BVCM =VG

M2 M3

VS

VG VG VG

MN1 MN3MN2

MP M5

M6

Amp1

VDD

Gain Control 2

Gain Control 1

ID ID

Vop

Von

IT

IB

2ID.B

1 : 1

1 : 1

1 : 1 1 : 1

ID.B+ID.T

ID.B-ID.T

IB

2ID.B

3(ID.B-ID.T)

1 : 1

ID.B-ID.T

ID.B-ID.T

2(ID.B+ID.T)

2ID.B

1 : 1

1 : 2

Gain control circuits

Electronics Laboratory, Physics Dept.

ICECS 2010

The two gain control circuits produce the appropriate currents that bias and control the gain of the VGA.

Variable Gain Amplifier

VP VN

M1

M1P M1N M4P M4N

M4

M4R

ID.B+ID.TID.BVCM =VG

M2 M3

VS

VG VG VG

MN1 MN3MN2

MP M5

M6

Amp1

VDD

Gain Control 2

Gain Control 1

ID ID

Vop

Von

IT

IB

2ID.B

1 : 1

1 : 1

1 : 1 1 : 1

ID.B+ID.T

ID.B-ID.T

IB

2ID.B

3(ID.B-ID.T)

1 : 1

ID.B-ID.T

ID.B-ID.T

2(ID.B+ID.T)

2ID.B

1 : 1

1 : 2

Amp1 stabilize output common-mode voltage

produce the diode loads bias current

Electronics Laboratory, Physics Dept.

ICECS 2010

Thus: the gmb-input equals to (IB+IT)/VR

the gmb-loads equals to (IB-IT)/VR

Variable Gain Amplifier

VP VN

M1

M1P M1N M4P M4N

M4

M4R

ID.B+ID.TID.BVCM =VG

M2 M3

VS

VG VG VG

MN1 MN3MN2

MP M5

M6

Amp1

VDD

Gain Control 2

Gain Control 1

ID ID

Vop

Von

IT

IB

2ID.B

1 : 1

1 : 1

1 : 1 1 : 1

ID.B+ID.T

ID.B-ID.T

IB

2ID.B

3(ID.B-ID.T)

1 : 1

ID.B-ID.T

ID.B-ID.T

2(ID.B+ID.T)

2ID.B

1 : 1

1 : 2

1exp(2 )

1

T

mb input B T Bv

TB Tmb load

B

II I I

xII II

gA

g

Electronics Laboratory, Physics Dept.

ICECS 2010

Voltage gain:

where x=IT/IB

Simulations Results

Technology : Standard 0.18um CMOSVDD=0.8V

IB=10uA/15uA/20uA

IT=50% of IB

Simulations Results

Gain range of the proposed and the conventional VGA approach against tuning current IT

-5.0 5.00.0-10 10IT (μΑ)

-12.5

-10.0

-7.5

-5.0

-2.5

0.0

7.5

2.5

5.0 Introduced approach

Conventional approach

Ga

in (

dB)

-10 -5.0 0.0 5.0 10IT (μΑ)

-400

-300

-200

-100

0.0

100

200

300

400

Err

or (

mdB

)

IB=20μΑ

IB=15μΑ

IB=10μΑ

Linearity error versus tuning current IT with bias current IB as a parameter (10uA, 15uA & 20uA).

Electronics Laboratory, Physics Dept.

ICECS 2010

Simulation Results

Gain variation of VGA versus tuning variable IT with bias current IB as parameter (10uA, 15uA & 20uA)

-10 -5.0 0.0 5.0 10IT (μΑ)

Ga

in (

dB

)

-12.5

-10.0

-7.5

-5.0

-2.5

0.0

2.5

5.0

7.5

IB=10μΑ

IB=15μΑIB=20μΑ

Electronics Laboratory, Physics Dept.

ICECS 2010

Simulations Results

IB1=10uA

IB2=15uA

IB3=20uA

Comments

Technology Standard 0.18um CMOS

VDD 0.8V

IDD 267uA 395uA 530uA -

IT variation ±5uA ±7.5uA ±10uA ±50% of IB

Gain range ≈17dB ≈17dB ≈17dB -

f-3dB @gain=6.5dB 21MHz 31MHz 42MHz Pout=-25dB : Pin=-31.5dB

f-3dB @gain=-10.5dB

95MHz 143MHz 195MHz Pout=-25dB : Pin=-15.5dB

THD @gain=-10.5dB

-67dB -68dB -69dB Pout=-25dB : Pin=-15.5dB

THD @gain=-10.5dB

-44dB -45dB -46dB Pout=-15dB: Pin=-

4.5dB

ConclusionsA low-voltage VGA was introduced.Based on master-slave techniqueUtilizes bulk-driven PMOS input transistorsImplements the pseudo exponential

approximation function :exp(2 )1

1xx

x

Electronics Laboratory, Physics Dept.

ICECS 2010

Conclusions

Benefits of the proposed VGA topology : a linear-in-dB gain range almost equal to

17dBlinear gain tunability less than ±0.5dB linear errorstability over process a doubled slope of gain curve

Electronics Laboratory, Physics Dept.

ICECS 2010

Thank YouFor your Attention!!!