AN-1026

One Technology Way P.O. Box 9106 Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 Fax: 781.461.3113 www.analog.com

ADCJohn Ardizzoni Jonathan Pearson

Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no

responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other

rights of third parties that may result from its use. Specifications subject to change without notice. No

license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

Trademarks and registered trademarks are the property of their respective owners.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781.329.4700 www.analog.com

Fax: 781.461.3113 ©2009 Analog Devices, Inc. All rights reserved.

VA

VA

RF1

RF2

VIP

VIN, dm

VIN

+

–

VOCM

RG1

RG2

VOUT, dm

VON

VOP

–

+

0826

3-00

1

1.

ADC2ADC

ADC ADC— —

-AD8138 ADC

1 ADC

ADC (VON) (VOCM)ADC

ADC VOP

VON VOCM (PN ) VOCM

VOCM VA+

VA–

VIP VIN

VIP – VIN

VIN, dm VIN, cm 12

VIN, dm = VIP – VIN (1)

3 4

VOUT, dm = VOP – VON (3)

VOUT, cm VOCM

ADCβ1 β2

5 6

2+ INIP VVVIN, cm = (2)

VOUT, cm = (4) 2+ ONOP VV

(5) 11

11 +

=GF

G

RRR

β

(6) 22

22 +

=GF

G

RRR

β

AN-1026

Rev. 0 | Page 2 of 16

2009 11 —— 0

.................................................................................................... 1

........................................................................................... 2

ADC ........................................... 3

(ICMVR) ................................................ 5

........................................... 6

................................................................................... 7

.................................................................................................... 7

.......................................................................................... 9

......................................................................................... 10

................................................................................ 11

............................................................................................. 11

PCB ........................................................................... 12

AN-1026

Rev. 0 | Page 3 of 16

RF

RF

RIN, dm VOCM

RG

RG

0826

3-00

2

2.

200

200

RL, dm = 100 VOCM

200

200

RT

= 133−

−

=

400−

1

100−

1

1RT

0826

3-00

3

3. 100 Ω

ADC β1 = β2 VIP VIN VOCM β1

β2 VOUT, dm β7 VOUT, dm

A(s)

β1 ≠ β2 VOCM

β1 = β2 ≡ β 7 8

A(s) → ∞RF/RG 1/β

ADC 9

ADC

180°

10

VOUT, cm VOCM

21

])(-)()(][ [ )+βA(s)(β+

-βV-β+V-ββV+ββ

=V INIPOCMOUT,dm

2121

212

1

112(7)

(8) ])A(s)(

11

1[ ][β

+=

G

F

IN,dm

OUT,dm

RR

VV

(9) G

F

IN,dm

OUT,dmv R

RVV

A ==

(10) ][log

out,dm

OUT,cm

VV

=ΔΔ

1020

ADC

ADC

ADCADC

ADCRT

ADC 2

RIN 2 × RG

RL RT 113 RF = RG = 200 Ω

RL, dm = 100 Ω RT = 133 Ω

(10)

INL

T

RR

R 111

=-

AN-1026

Rev. 0 | Page 4 of 16

2V

0V

–2V

3.5V

2.5V

1.5V

3.5V

2.5V

1.5V

1.75V

1.25V

0.75V

RF500

RF500

VOCM VOUT, dm2.5V

RG500

RG500

VINVON

VOP

–

+

0826

3-00

4

4. ADC

4 ADC

200

200

VOCM VOUT, dm2.5V

200

200267

VON

VOP

–

+

0826

3-00

5

5.

61.5

762 Ω1

05 Ω1

1=

−=TR

200

200

VOCM VOUT, dm2.5V

200

20050

2V p-p

VON

VOP

–

+

RT61.5

0826

3-00

6

6.

RTH27.6

VTH1.1V p-p

0826

3-00

7

7.

.

RTS27.6

RF200

RF200

VOCM VOUT, dm2.5V

RG200

RG200

RTH27.6

VTH1.1V p-p

VON

VOP

–

+

0826

3-00

8

8.

12 267 Ω 13267 Ω 50 Ω RT 61.5 Ω

6 50 Ω2 V p-p 50 Ω

1 V p-p

RG

61.5 Ω 50 Ω

RG

7

27.6 Ω RTS

8

(13)

VIN, dm VIN RF RG

VOP − VON

4 V p-p VOUT, cm VOCM = 2.5 VVA+ VA− VOP/2

3 4 VOP = VOCM + VIN/2 ±1 V2.5 V VON = VOCM – VIN/2 ±1 V 2.5 VVA+ VA− ±0.5 V 1.25 V VIN

(2 V – 0.5 V)/500 Ω = 3 mAVIN 667 Ω

12 RIN, se

RG RG

5 150 Ω 200 Ω

(12) ( ))RR(

RR

R

FG

F

Gse,IN

+×2

=-1

AN-1026

Rev. 0 | Page 5 of 16

RF205

RF205

VOCM VOUT, dm2.5V

RG200

RG200

RS50

2V p-p

VON

VOP

–

+

RT61.9

RTS28

RIN, se

0826

3-00

9

9.

A

–IN +IN

Q2 Q3

Q1 Q4

0826

3-01

0

10. ( ICMVR)

1.1 V p-p 1 V p-p27.6 Ω

(>1 kΩ) 1 2

814

1 V p-p15

9 1%

(14)

(15)

p-Vp( p-Vp 970=6227

20011= .)..V dm,OUT Ω

Ω

=11

6227= ).VDesired

.R OUT,dF p-Vp

( Ω ΩΩ 9206=

111

6227 .)..

p-Vpp-.0Vp(

9 RF RG

RIN, se

200 Ω 200 Ω + 28 Ω = 228 ΩRIN, se β

16 17

RIN, se 18

267 Ω RT

RIN, se RT

(16)

(17)

(18)

4940=405200

=+

=1 .RR

RΩΩ

βGF

G

5270=433228

=++

+= .

RRRRR

ΩΩ

βTSGF

TSG2

Ωββ

ββ271=

1++

=21

21

)()(GRRIN，N，

1 2RTS RG 18 RIN, se

12

ADIsimDiffAmp™ ADI Diff Amp Calculator™

www.analog.com

(ICMVR)

ICMVRICMV Vacm

VA±

VIN, cm β VOCM

(VA±) β 19 β20

VA ( 4 )ADI ADC

ADC 1 V ()

–VS 10(Q2 Q3)

(19)

(20)

21

21IN11IPOCM21 )-(1)-(12

ββββββββ

+++

=±

VVVVV Aacm

)-( , ICMOCMCMINAacm VVVVV β+=±

PNP(Q1 Q4) Vbe

–IN –0.3 V A 0.7 VPNP( ) A –0.3 V NPN

AN-1026

Rev. 0 | Page 6 of 16

1. ADC

(V)

(V)

ISUPPLY

(mA)

ADC ICMVR VOCM

(MHz) (V/μs) (nV) ±5 V +5 V +3.3 V +3 V ±5 V +5 V +3.3 V +3 V

AD8132 350 1200 8 –4.7 +3 0.3 3 0.3 1.3 0.3 1 ±3.6 1 3.7 N/A 0.3 1 ±1 12 AD8137 76 450 8.25 –4 +4 1 to 4 1 2.3 1 2 ±4 1 4 1 2.3 1 2 3.2

AD8138 320 1150 5 –4.7 +3.4 0.3 3.2 N/A N/A ±3.8 1 3.8 N/A N/A ±1.4 20 AD8139 410 800 2.25 –4 +4 1 4 N/A N/A ±3.8 1 3.8 N/A N/A 25

ADA4927-1/ ADA4927-2

2300 5000 1.4 –3.5 +3.5 1.3 3.7 N/A N/A ±3.5 1.5 3.5 N/A N/A ±1.2 20

ADA4932-1/ ADA4932-2

1000 2800 3.6 –4.8 +3.2 0.2 3.2 N/A N/A ±3.8 1.2 3.2 N/A N/A ±1 9

ADA4937-1/ ADA4937-2

1900 6000 2.2 N/A 0.3 3 0.3 1.2 N/A N/A 1.2 3.8 1.2 2.1 N/A ±0.9 40

ADA4938-1/ ADA4938-2

1000 4700 2.6 –4.7 +3.4 0.3 3.4 N/A N/A ±3.7 1.3 3.7 N/A N/A ±1.2 37

ADA4939-1/ ADA4939-2

1400 6800 2.3

N/A 1.1 3.9 0.9 2.4 N/A N/A 1.3 3.5 1.3 1.9 N/A ±0.8 37

RF

VOCM

RGCIN

RFRGCIN

0826

3-01

1

11. ADC

RF

RF

VOCMADCCMV

TOADC

ROUT

ROUT

RG

RG

COUT

COUT

0826

3-01

2

12.

1 ADI ADCICMVR

ADC

11

VOCM

ADC

ADC

ADC

ADCADC

VOCM

ADC

ADC ( 12 )ADC ADC

5 V VOCM = 2.5 V ADC 1.8 VADC CMV 0.9 V

AN-1026

Rev. 0 | Page 7 of 16

2.

–120

–110

–100

–90

–80

–70

–60

–50

–40

–30

–20

1.4 1.6 2.01.8 2.2 2.4 2.6 2.8 3.0 3.2 3.4

HA

RM

ON

IC D

IST

OR

TIO

N (

dB

c)

VOCM (V)

VOUT = 2V p-p

HD2 @ 10MHz

HD3 @ 10MHz

HD2 @ 30MHz

HD3 @ 30MHz

0826

3-01

3

13. ADA4932 VOCM( 5V)

(21)

( )

2 ADC

ADC ADCADC

ADCADC

1ADC

13 ADA4932 VOCM

1.2 V/ VOCM VPEAK

(1 V) 2.8 V (3.8 VPEAK

5 V 1.2) 2.2 V(–1 VPEAK)

ADC

ADC (n)(n)

ADCADC

ADCADC

ADCn ADC 2n

(LSB) q1/2n n ADC

ADC

122

1=

12=

n

q

AN-1026

(24)

+

RF2

Vno, dm

VnCM

VOCM

VnIN

RF1

RG2

RG1

VnRF1

VnRF2

VnRG1

VnRG2

inIN+

inIN–

0826

3-01

4

14. ADC

n ADC- (dB) ( 22) n

- (dB) = 6.02n + 1.76 dB (22)

ADCADC

(THD + N) ADCADC

23THD

THD+ =

v1 v2 v6 ADCvn

THD + (SINAD)( 24)

2

22222

(rms)][(rms)][(rms)][(rms)][(rms)][(rms)][

1

265432 +++++

ννννννν n

(23)

] 1 [log 20= 10 THD+N

)dB(SINAD

(27)

- ( 22) SINAD- SINAD( 25)

(ENOB)

SINAD(dB) = 6.02(ENOB) + 1.76 dB (25)

ENOB SINAD 26

ENOB ADC ADCADC 14

ADC

(26) 026

=.

ENOBdB 1.76-SINAD(dB)

β1 = β2 ≡ β27

ββββββ

===+

= 2121

v

2v

v nINnINnIN ，v dm,no

βββββββ

==0=+

= 2121

21 ，v dm,no )-(2v

v nCMnCM

ββββββ

===+

1= 211

21

11++ )( )(

)-(2 nIN

nIN ，RiRi

iv FnIN+G

dm,no

21

ββββββ

===+

1= 212

21 )( )( )-(2

--nIN

-nIN ，RiRi

iv FnING

dm,no

βββ

βββ

===+

= 211

11

21

11 )( 4)-)(14(2

nRG1 ，RR

kTRkTR

vvG

FG

Gdm,no

βββ

βββ

===+

= 212

22

21

22 )( 4)-)(14(2

nRG2 ，RR

kTRkTR

vvG

FG

Gdm,no

21

βββββ

β===

+= 211

11 4)4(2

nRF1 ，kTRkTR

vv FF

dm,no

βββ

βββ

===+

= 21221

21 4)4(2

nRF2 ，kTRkTR

vv FF

dm,no

Rev. 0 | Page 8 of 16

AN-1026

Rev. 0 | Page 9 of 16

VOCM

8

2

1

5

4

–OUT

+OUT

3

6

U1AD8138AR

C110nF

C210nF

L1

L2

V+

V–

0826

3-01

5

15.

vno, dm

ADI Diff Amp CalculatorADC www.analog.com

ADC ADC ENOB2 AD9445 ADC 5 V

2 V50 MHz (−3 dB)

ENOB50 MHz ENOB = 12

ADA4939 ADCAD9445

RF = 402 Ω RG = 200 Ω 29.7 nV√Hz

BN

BN π/2 3 dB 28

(28)

( 29)

vno, dm (rms) = (9.7 nV/√Hz)(√78.5 MHz)

= 86 μV rms (29)

99.7%±3σ

vno, dm (p-p) ≈ 6(86 μV rms) = 516 μV p-p (30)

AD9445 LSB 1 LSB ENOB 12

2V 31

LSB = 2 V/212 = 488 μV (31)

12 ENOBADC LSB

ADC

MHz 78.5MHz )( =2

=π

NB 50

ADC1 ADC

ICMVR

(PSR)

ADA4937-1 50 mV p-p 50 MHz50 MHz −70 dB

16 μV 1 V16 1 LSB 15.3 μV

1 LSB

SMT L1 L2C1 C2( 15)

50 MHz 60 Ω 10 nF (0.01 μF)0.32 Ω 45.5 dB

32

–70 dB 115 dB90 nV p-p 1 LSB

)(60+320

320..

= 20log = −45.5 dB (32)

AN-1026

Rev. 0 | Page 10 of 16

3. ADA4939

(dBc)

HD2 @ 10 MHz −102 HD2 @ 70 MHz −83 HD2 @ 100 MHz −77 HD3 @ 10 MHz −101 HD3 @ 70 MHz −97 HD3 @ 100 MHz −91

–60

–110

–105

–100

–95

–90

–85

–80

–75

–70

–65

1 10 100

HA

RM

ON

IC D

IST

OR

TIO

N (

dB

c)

FREQUENCY (MHz)

HD2, VS (SPLIT SUPPLY) = ±2.5V

HD3, VS (SPLIT SUPPLY) = ±2.5V

HD2, VS (SPLIT SUPPLY) = ±1.65V

HD3, VS (SPLIT SUPPLY) = ±1.65V

VOUT, dm = 2V p-p

HD2 –88dBc @ 50MHz

0826

3-01

6

16.

ADA4939 AD9445 12 ENOB 2V1 LSB ENOB LSB 488 μV

ADA4939 22 3 3 2

2 V p-p

(50 MHz) HD2 HD3

50 MHz “ ”25 MHz

50 MHz

16 2 V p-p ADA4939

2 V p-p 50 MHz HD2 −88 dBc1 ENOB LSB

33

(33)

80 μV p-p 1 ENOB LSB 16%ADA4939 AD9445 ADC

ADC

1/(1 + LG) LG

( ) A(s)β

A(s) × β(A(s) β )

A(s) 1 1/fA(s)

A(s)

T(s)1/RF

T(s) × (1/RF) = T(s)/RF A(s) T(s)

1/RF

( ADA4927)

p-p μV 80 ≈)p)(10-(2Vp 20-88

=HD2

AN-1026

Rev. 0 | Page 11 of 16

–40

–50

–60

–70

–80

–90

–100

–110

–120

–1301 10 100 1k

FREQUENCY (MHz)

SP

UR

IOU

S-F

RE

E D

YN

AM

IC R

AN

GE

(d

Bc)

VOUT, dm = 2V p-p

G = 1

G = 10

G = 20

0826

3-01

7

17.

–50

–60

–70

–80

–90

–100

–110

–1201 10 100

DIS

TO

RT

ION

(d

Bc)

FREQUENCY (MHz)

HD2, G = 1, RF = 200

HD3, G = 1, RF = 200

HD2, G = 2, RF = 402

HD3, G = 2, RF = 402

0826

3-01

8

18. ADA4937 ADC

17 ADA4927

ADC

ENOB (EUBW)ADC

−3 dB−3 dB −3 dB

18 −80 dBc60 MHz ADC

( )

VO = VP sin 2πft (34)

34

dv/dt maxVP

f (FPBW) FPBW

ADC(FPBW)

ADC

PCB

( A(s) × β)ADC

7 8 37(β1 ≠ β2)

βA(s) × β

−1−180° +1

1( 0 dB) A(s)

1 + RF/RG

A(s)1 0 dB A(s)

−180°45°

pmax fvdtdv

π2= (35)

(36) Vp

FPBWπ2

=

(37)2

+=

)(s)( 21 ββA

AN-1026

Rev. 0 | Page 12 of 16

80

–80

–60

–40

–20

0

20

6

40

60

90

–270

–225

–180

–135

–90

–45

0

45

1k 10k 100k 1M 10M 100M 1G 10G

GA

IN (

dB

)

PH

AS

E (

Deg

rees)

FREQUENCY (Hz)

GAIN

PHASE

PHASEMARGIN 70°

LOOPGAIN = 0dB

(6dB)1 + = 2RF

RG

0826

3-01

9

19. ADA4932

1k

100

10

1

0.3

0.1

50

0

–50

–100

–150

–20010 100 1k 10k 100k 1M 10M 100M 1G 10G

FREQUENCY (Hz)

IMP

ED

AN

CE

MA

GN

ITU

DE

(k

)

IMP

ED

AN

CE

PH

AS

E (

Deg

rees)

MAGNITUDE

PHASE

–135

–180

PHASEMARGIN 45°

0826

3-02

0

20. ADA4927

19 ADA4932 RF/RG = 1( = 2)

19 1( 100%)ADA4932 50° ADC

ADA4932( RF/RG = 0.25 = 1.25)

ADC ADC

ADCA(s)

T(s)T(s)/RF T(s) = RF

1( 0 dB)

1 kΩ20 ADA4927 ADC RF

= 300 Ω

0 dB 300 ΩT(s) −135° +45°

RF

PCB

ADC PCB

PCB 20°

RF RF

RF CF

RFCF RG

PCB

PCB

ADC

FR-4 50 Ω PCB 2.8 pF/7 nH/ 50 Ω

30%

AN-1026

Rev. 0 | Page 13 of 16

R4

R5

VOCMC1

TOADC

R2

R3

R6

R7

C6

C7U1

RS

RT

R1

C2

C3

C4

C5

+VS

–VS

0826

3-02

1

21. ADC

R2

RT

R4

R6

R7

R1 R3 R5

U1

(a)

C2

C6

C7

C4

C3

C5C1

(b)

0826

3-02

2

22. (a) (b)

DIGITAL

CIRCUITSMIXED

SIGNALS

VA VD

VA VD

AGND DGND

ANALOGCIRCUITS

DIGITAL SUPPLYANALOG SUPPLY

DIGITALCIRCUITS

A A D

A D

D

ANALOGCIRCUITS

SYSTEMSTAR

GROUND

0826

3-02

3

23.

VOCM

21

ADC

ADC (22)

( 22)

IC

(23)

(PCB)www.analog.com

ADC

ADC

AN-1026

Rev. 0 | Page 14 of 16

AN-1026

Rev. 0 | Page 15 of 16

AN-1026

Rev. 0 | Page 16 of 16

©2009 Analog Devices, Inc. All rights reserved. Trademarks and

registered trademarks are the property of their respective owners.

AN08263-0-11/09(0)