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)