Amplifiers: Capture Signals and Drive Precision Systems (Design Conference 2013)

Amplifiers: Capture Signals and
Drive Precision Systems
Advanced Techniques of Higher Performance Signal Processing

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2

Today’s Agenda
Operational amplifier design and applications
Op amp noise considerations
Instrumentation amplifiers and applications
ADC driver amplifiers
High common mode voltage applications
Amplifier design tools
3

Analog to Electronic Signal Processing
SENSOR
(INPUT)
DIGITAL
PROCESSOR
AMP CONVERTER
ACTUATOR
(OUTPUT)
AMP CONVERTER
4

SENSOR
(INPUT)
DIGITAL
PROCESSOR
AMP CONVERTER
ACTUATOR
(OUTPUT)
AMP CONVERTER
5

Amplifiers and Operational Amplifiers
Amplifiers
 Make a low-level, high-source impedance signal into a high-level, low-source
impedance signal
 Op amps, power amps, RF amps, instrumentation amps, etc.
 Most complex amplifiers built up from combinations of op amps
Operational amplifiers
 Three-terminal device (plus power supplies)
 Amplify a small signal at the input terminals to a very, very large one at the
output terminal
6

Operational Amplifiers
Operational
 Op amps can be configured with feedback networks in multiple ways to perform
“operations” on input signals
 “Operations” include positive or negative gain, filtering, nonlinear transfer
functions, comparison, summation, subtraction, reference buffering, differential
amplification, integration, differentiation, etc.
Applications
 Fundamental building block for analog design
 Sensor input amplifier
 Simple and complex filters – antialiasing
 ADC driver
7

Original Vacuum-Tube Op Amp from Philbrick Research in
1953: It Used 300 V Supplies
8

AD823 JFET Input Op Amp Simplified Schematic
INPUTS
+VS
-VS
Q57
A=19
Q44
A=1
Q43
Q58
Q62
R44
S1NS1P
VB
Q49Q61Q72
J6J1
Q48
Q35Q53
I1 Q56
Q59
A=1
Q17
A=19
OUTPUTQ60
R28
(-)
(+)
VBE + 0.3V
BIAS CURRENT = 25pA MAX @ +25 C
INPUT OFFSET VOLTAGE = 0.8mV MAX @ +25 C
INPUT VOLTAGE NOISE = 15nV/Hz
INPUT CURRENT NOISE = 1fA/Hz
9

Key Op Amp Performance Features
Bandwidth and Slew Rate
 The speed of the op amp
 Bandwidth is the highest operating frequency of the op amp
 Slew rate is the maximum rate of change of the output
 Determined by the frequency of the signal and the gain needed
Offset Voltage and Current
 The errors of the op amp
 Determines measurement accuracy
Noise
 Op amp noise limits how small a signal can be amplified with good fidelity
10

Standard Configurations
Non-Inverting R1
+
-
R2
VIN
VOUT
V1I1
Vin
1
1
R
V
I
in
 21 II 
)(
0
1
2
2
1
R
R
VV
R
R
V
V
inout
in
out


;
1
1
1
R
V
I 1VVin 
)1(
1
2
1
2
1
1
1
R
R
VV
R
R
V
VV
out
out


;
I2
Inverting
+
-
R1
R2
VIN
VOUT
Vin
I1
Virtual Ground
Because +VIN = -VIN
11

Op Amp Error Sources
12
IDEAL
OFFSET VOLTAGE (Vos)
INPUT IMPEDANCE (ZIN)
INPUT BIAS CURRENT (Ib)
INPUT OFFSET CURRENT
(Ios)
A
+
-
-+
OUTPUT IMPEDANCE
(ZOUT)
 IB – The Current into the Inputs
[~pA to mA]
 Vos – The Difference in Voltage
Between the Inputs [µV to mV]
 IOS – The Difference Between the
+ IB and – IB [~IB /10]
 ZIN – Input Impedance [MW to GW]
 ZOUT – Output Impedance [<1 W]
 Avo – Open Loop Gain [V/mV]
 BW – Finite Bandwidth [ kHz to GHz)

AN “IDEAL” NON-INVERTING AMPLIFIER
13
+
-
Vin
Vout
I1
R1
R2
V1
Vid
1VVV idin 
outV
RR
R
V *
21
1
1


))(1(
1
2
idinout VV
R
R
V 

DC + AC Errors of a Circuit
PSRR
Vs
CMRR
V
en
A
V
RIVV
icm
vo
out
sBosid

 *
14
)(
1
idinout VVV 

))*((
1
PSRR
Vs
CMRR
V
en
A
V
RIVVV
cm
vo
out
sBos
in
out



0_ vGAINLOOP A
Since en gets multiplied by 
1
we get the name “noise gain”
+
-
R
2
Rs
Vout
Vid
Vin

Noise Gain: The noise gain of an op amp can
never be less than the signal gain
+
-
IN +
-
+
-
A B C
R1
R2 IN
R1
R2
R2
R1
IN
Signal Gain = 1 + R2/R1
Noise Gain = 1 + R2/R1
Signal Gain =- R2/R1
Noise Gain = 1 +
R2
R1 R3
 Voltage Noise and Offset Voltage of the op amp are reflected to the
output by the Noise Gain.
 Noise Gain, not Signal Gain, is relevant in assessing stability.
 Circuit C has unchanged Signal Gain, but higher Noise Gain, thus
better stability, worse noise, and higher output offset voltage.
IN
A B C
R1
R2 IN
R1
R2
R2
R1
IN
Signal Gain = R2/R1
Signal Gain =
Noise Gain = 1 +
R2




+
-
IN +
-
+
-
A B C
R1
R2 IN
R1
R2
R2
R1
IN
Noise Gain = 1 +
R2
R1 R3



IN
A B C
R1
R2 IN
R1
R2
R2
R1
IN
Signal Gain = R2/R1
Signal Gain =
Noise Gain = 1 +
R2




+
-
IN +
-
+
-
A B C
R1
R2 IN
R1
R2
R2
R1
IN
Noise Gain = 1 +
R2
R1 R3
 Voltage Noise and Offset Voltage of the op amp are reflected to the
output by the Noise Gain.
 Noise Gain, not Signal Gain, is relevant in assessing stability.
 Circuit C has unchanged Signal Gain, but higher Noise Gain, thus
better stability, worse noise, and higher output offset voltage.
IN
A B C
R1
R2 IN
R1
R2
R2
R1
IN
Signal Gain = R2/R1
Signal Gain =
Noise Gain = 1 +
R2




+
-
IN +
-
+
-
A B C
R1
R2 IN
R1
R2
R2
R1
IN
Noise Gain = 1 +
R2
R1 R3



IN
A B C
R1
R2 IN
R1
R2
R2
R1
IN
Signal Gain = R2/R1
Signal Gain =
Noise Gain = 1 +
R2




15

Total Noise Calculation
FCL = CLOSED LOOP BANDWIDTH
R1
V
ON
Rp
In-
In+
R2
V
n
V
R2J
V
R1J
V
RPJ
+
= BW [(In-2)R2
2] [NG] + [(In+2)RP
2] [NG] + VN
2 [NG] + 4kTR2 [NG-1] + 4kTR1 [NG-1] + 4kTRP [NG]VON
BW = 1.57 FCL
FCL = CLOSED LOOP BANDWIDTH
R1
V
ON
Rp
In-
In+
R2
V
n
V
R2J
V
R1J
V
RPJ
+
R1
V
ON
Rp
In-
In+
R2
V
n
V
R2J
V
R1J
V
RPJ
+
= BW [(In-2)R2
2] [NG] + [(In+2)RP
2] [NG] + VN
2 [NG] + 4kTR2 [NG-1] + 4kTR1 [NG-1] + 4kTRP [NG]VON = BW [(In-2)R2
2] [NG] + [(In+2)RP
2] [NG] + VN
2 [NG] + 4kTR2 [NG-1] + 4kTR1 [NG-1] + 4kTRP [NG]VON
BW = 1.57 FCL
16

Dominant Noise Source Determined
by Input Impedance
CONTRIBUTION
FROM
AMPLIFIER
VOLTAGE NOISE
AMPLIFIER
CURRENT NOISE
FLOWING IN R
JOHNSON
NOISE OF R
VALUES OF R
0 3k 300k
3 3 3
0
0
3
7
300
70
RTI NOISE (nV /  Hz)
Dominant Noise Source is Highlighted
R
+
–
EXAMPLE: OP27
Voltage Noise = 3nV / Hz
Current Noise = 1pA / Hz
T = 25°C
OP27
R2
R1
Neglect R1 and R2
Noise Contribution
CONTRIBUTION
FROM
AMPLIFIER
VOLTAGE NOISE
AMPLIFIER
CURRENT NOISE
FLOWING IN R
JOHNSON
NOISE OF R
VALUES OF R
0 3k 300k
3 3 3
0
0
3
7
300
70
RTI NOISE (nV /  Hz)
Dominant Noise Source is Highlighted
R
+
–
EXAMPLE: OP27
Voltage Noise = 3nV / Hz
Current Noise = 1pA / Hz
T = 25°C
OP27
R2
R1
Neglect R1 and R2
Noise Contribution
17
AD8675
AD8675

1/f Noise Bandwidth
 1/f Corner Frequency is a figure of merit for op amp
noise performance (the lower the better)
 Typical Ranges: 2Hz to 2kHz
 Voltage Noise and Current Noise do not necessarily
have the same 1/f corner frequency
3dB/Octave
WHITE NOISE
LOG f
CORNER
1
f
NOISE
nV / Hz
or
Hz
en, in
k
FC
k FC
1
f
en, in =
3dB/Octave
WHITE NOISE
LOG f
CORNER
1
f
NOISE
nV / Hz
or
pA / Hz
en, in
k
FC
k FC
1
f
en, in =
 1/f Corner Frequency is a figure of merit for op amp
noise performance (the lower the better)
 Typical Ranges: 2Hz to 2kHz
 Voltage Noise and Current Noise do not necessarily
have the same 1/f corner frequency
3dB/Octave
WHITE NOISE
LOG f
CORNER
1
f
NOISE
nV / Hz
or
Hz
en, in
k
FC
k FC
1
f
en, in =
3dB/Octave
WHITE NOISE
LOG f
CORNER
1
f
NOISE
nV / Hz
or
pA / Hz
en, in
k
FC
k FC
1
f
en, in =
18

The Peak-to-Peak Noise in the 0.1 Hz to
10 Hz Bandwidth ADA4528
19
ADA4528
97nV p-p

ADA4528-x World’s Most Accurate Op Amp Low
Noise Zero-Drift Amplifier
 Key Features
 Lowest noise zero-drift amp
 5.6 nV/√Hz noise floor
 No 1/f noise
 High DC accuracy
 Low offset voltage: 2.5 µV max
 Low offset voltage drift: 0.015 µV/ºC max
 Rail-to-rail input/output
 Operating voltage: 2.2 V to 5.5 V
 Applications
 Transducer applications
 Temperature measurements
 Electronic scales
 Medical instrumentation
 Battery-powered instruments
20
Vos TCVos Isy / Amp CMRR Bandwidth Slew Rate Temp Range Op. Supply
2.5 V max 0.015 V/ºC max 1.8 mA max 115 dB min 4 MHz 0.4 V/s -40 C - 125 C 2.2 V to 5.5 V
ADA4528-1 Single Released ADA4528-2 Dual In Development
Package: 8-lead MSOP, 8-lead LFCSP-8 (3 x 3)
Price: $1.15 1ku
 Package: 8-lead MSOP, 8-lead LFCSP (3 x 3)
 Sample Availability: Now
No 1/f Noise
5.6nV/Hz 
ADI Advantages
World’s Most Accurate Op Amp, Lowest Voltage Noise Zero-
Drift Op Amp

Precision Weigh Scale Design Using the AD7791
24-Bit Sigma-Delta ADC with External ADA4528-1
Zero-Drift Amplifiers (CN0216)
21
24-bit
ADC
Noise optimized for
DC measurements

1-22
1) More capacitance, more noise peaking
2) Total noise at the output = value of the
noise spectral density integrated over the
entire bandwidth
3) Noise is dominated by the noise peak.
4) Assuming system –3 dB bandwidth of
16 MHz (25 MHz noise bandwidth)
CL = 8 pF CL = 220 pF CL = 470 pF
95 µV rms 110 µV rms 115 µV rms

ADI Amplifiers
Based on Process Innovations
Advanced Process Technology
 Bipolar
 JFET
 CMOS
 iCMOS® High Performance, Low Noise CMOS Process
 iPolar® High Performance, Low Noise Bipolar Process
 LD20 Enhanced CMOS
23

Precision Amplifier Enablers
•Overvoltage Protection
•Zero Crossover Distortion
•Zero-Drift Op Amp
•Bias Cancellation Circuitry
Design
Techniques
•Low Noise Processes
•High Voltage Processes
•Feature Rich Processes
Process
Technology
•DigiTrim / In Pkg Trim
•Laser Trim
Trim
Techniques
•Micro Packages
•WLCSP/ Bumped Die
•Low Stress Polyimide
Package
Technology
•Strip Testing
•TCVOS on Strip
Test
Techniques
24
•Improved Robustness
•Higher Performance Amplifiers
•Higher Precision in Small Plastic Packages
•High Precision CMOS Products
•Higher Precision in Small Plastic Packages
•Greater User Flexibility - Small Form Factors
•Greater Functionality in Small Footprint
• Higher Precision, Improves Offset and TCVOS
Performance
Resulting Benefits
•Ultralow Noise AMP/REF Designs
•Higher Voltage Amplifiers (100 V)
•Higher Integration and Added Features

AD8597/9
1 nV/√Hz Ultralow Noise
 Key Benefits
 Low Noise, High Precision
 Low Voltage Noise: 1 nV/Hz at 1 kHz, 76 nV
from 0.1 Hz to 1 Hz
 Low Current Noise: 1.5 pA/√Hz
 Unity Gain Stable with High 50 mA Output Drive
 ±5V to ±15V Operation
25
Noise THD+N Vos CMRR Bandwidth Slew Rate Temp Range Price @ 1k
1 nV/√Hz –105 dB 120 V max 120 dB 10 MHz 16 V/s
–40 C to
85 C
See website
 8-lead SOIC and 8-lead
LFCSP (3x3)
 Released
 SOIC
 Released
AD8597 Single AD8599 Dual
OUT A 1
- IN A 2
+ IN A 3
- V 4
+ V8
OUT B7
- IN B6
+ IN B5
AD8599
TOP VIEW
(Not to Scale)
OUT A 1
- IN A 2
+ IN A 3
- V 4
+ V8
OUT B7
- IN B6
+ IN B5
AD8599
TOP VIEW
(Not to Scale)
 Applications
 Professional audio preamps
 ATE
 Imaging systems
 Medical instrumentation
 Precision detectors

Optimizing AC Performance in an 18-bit,
250 kSPS, PulSAR Measurement Circuit
(CN0261)
26
Noise optimized for
Mid-range frequencies

SENSOR
(INPUT)
DIGITAL
PROCESSOR
AMP CONVERTER
ACTUATOR
(OUTPUT)
AMP CONVERTER
27

20-Bit, Linear, Low Noise, Precision, Bipolar
±10 V DC Voltage Source (CN0191)
28
1 – ppm resolution
Needs low noise
In all components

Without Buffer
29
DNL vs. Code INL vs. Code

Using a Rail-to-Rail Input Amplifier
30
Crossover point = 1.7 V away from rail.
INL vs. CodeDNL vs. Code

SOLUTION: ADA4500 Zero Crossover Amp
31
DNL vs. Code INL vs. Code

What Can Op Amps Do?
Op amps can do anything
 Amplify
 Filter
 Level shift
 Compare
 Drive
The circuit design becomes difficult
 Matching multiple amplifiers
 Circuit complexity
 Precision passive components
32

Specialty Amplifiers
Specialty Amplifiers
 Designed for a specific signal type
 Extract and amplify only the signal of interest
 Pick off a small differential signal from a large common-mode voltage
 Capture and demodulate a low-level AC signal
 Compress a high-dynamic range signal
 Provide automatic or controlled gain-changing
 Send and receive precision signals
 Provide high-speed low-impedance power output
 Use the analog domain to its best advantage to prepare a clean signal for the
data converter
33

Integrated “Amplifier” Products
34
2k2k
Z
V
YYXX


10
)21()21(
Current
Sense
Difference
Amps
Instrumentation
Amplifiers
VGAs
MultipliersRMS-DC Converters Thermocouple
Amplifiers
5mV/C
 
T
mRMS dtT
T
VV
0
2
sin
1

Single-Ended vs. Differential Signals
Single-ended signals
 Signal is measured referred to ground
 When signals are bipolar (+ and –), negative supplies needed
 AC signals are typically bipolar or need special “floating,” or capacitive coupling
 Ground often carries high noise from other signals or power, compromising the
signal
Differential signals
 Both sides of the signal float “off ground”
 Signals are separated from ground and other signals
 High frequency and accuracy usually need differential handling
 Common mode (average) can be set for single supply
 Specialized differential/difference amplifiers are needed
35

Instrumentation, Difference, and Differential
Amplifiers
Instrumentation Amplifiers
 Amplify differential inputs to a single-ended output
 Normally both amplifier inputs are high impedance
 Provide high gain (up to 10,000) and low noise
 Normally handle low-level signals from sensors
Difference Amplifiers
 Amplify differential inputs from high common-mode voltage levels
 Often include input attenuator to allow operation outside supplies
 High common-mode rejection even at high frequencies
Differential Amplifiers
 High frequency amplifiers with differential input and output
 Handle higher-level signals at lower gains
 Typically used for line driving/receiving and ADC driving
36

Op Amp Subtractor or Difference Amplifier
37
VOUT = (V2 – V1)
R2
R1
R1 R2
_
+
V1
V2
VOUT
R1' R2'
R2
R1
=
R2'
R1'
R2'
R1'
CRITICAL FOR HIGH CMR
0.1% TOTAL MISMATCH YIELDS  66dB CMR FOR R1 = R2
CMR = 20 log10
1 +
R2
R1
Kr
Where Kr = Total Fractional
Mismatch of R1/ R2 TO
R1'/R2'
EXTREMELY SENSITIVE TO SOURCE IMPEDANCE IMBALANCE
REF

AD8271 : Precision Difference Amplifier with
Programmable Gain
38
KEY SPECIFICATIONS
Difference Amplifier: G = ½, 1, 2
Single-ended Amplifier: G = -2 to +3
Low Distortion: 110 dB THD + N
Typical (G=1)
15 MHz Bandwidth
80 dB Min CMRR (G=1)
0.08% Max Gain Error
2 ppm/°C Max Gain Drift
2.6 mA Max Supply Current
Wide Power Supply Range: ±2.5 V to
±18 V
Key Benefits
 Low Distortion  Higher Performance
 Versatile Gain Configurations  Easy to Use
Target Applications
 High Performance Audio/Video
 In-Amp Building Block
 ADC Driver
1
7
6
10kΩ
AD8271
10kΩ
10kΩ
10kΩ
20kΩ
20kΩ
10kΩ
–VS
P4
P3
P2
P1
+VS
OUT
N1
N2
N3
07363-032
10
9
8
2
3
4
5

AD8270/AD8271 Flexible Gain Configurations
39
=
07363-053
1
7
10kΩ
AD8271
10kΩ
10kΩ
10kΩ
20kΩ
20kΩ
10kΩ
P4
P3
P2
P1
+IN
GND OUT
OUT
N1
N2
N3
10
9
8
2
3
4
–IN
–IN
+IN
5kΩ
5kΩ
10kΩ
10kΩ
GND
=
–IN
+IN
10kΩ
5kΩ
5kΩ
10kΩ
GND
07363-055
1
7
10kΩ
AD8271
10kΩ
10kΩ
10kΩ
20kΩ
20kΩ
10kΩ
P4
P3
P2
P1
OUT
OUT
N1
N2
N3
10
9
8
2
3
4
–IN
GND
+IN
OUT
G = ½, Ground Reference
G = 1, Mid-Supply Reference
G = 2, Ground Reference
More in Datasheet

AD8271 Application Example: Building High
Speed In-Amp
CN0122: High Speed Instrumentation Amplifier Using the AD8271
Difference Amplifier and the ADA4627-1 JFET Input Op Amp
Gain-bandwidth product of 20MHz at gain of 200
 www.analog.com/CN0122
 Uses monolithic difference amplifier for the output amplifier, thereby providing
good dc/ac accuracy with fewer components
40

AD8277 Application Example – Precision
Absolute Value Circuit
Benefits
 One single component
 Cost competitive
 Simple single-supply operation
 Wide input and supply range
 Low supply current
 Higher performance
 Fast 0 V crossover response
 Gain accuracy
 Offset voltage, temp drifts
 Low noise gain
41
AD8277
A1
–
+
AD8277
A2
–
+
VIN
VOUT = | VIN |
R
R
R
R
R
R
R
R
A1
–
+
A2
–
+
VIN
VOUT = | VIN |
R1
R2
R4
R3 R5
D1
D2
R1, R2, R3 = 10kΩ
R4, R5 = 20kΩ
Conventional precision absolute value circuit requires
many fast, high precision (i.e., expensive) components,
and has performance issues.

AD8276/AD8277/AD8278/AD8279 Applications –
Building Current Sources (Continued)
42
R1
R2
Rload
V+
Io
Vref
Vload
Vout
AD8276
Rg1 40kΩ
-IN
Rg2 40kΩ
Rf1 40kΩ
+
–2
3
+IN
4
-VS
1
REF
6
OUT
5
7
+VS
Rf2 40kΩ
SENSE
R1
Rload
+V
Io
Vref
Vload
AD8603
+5V
Vout
4 4
3
1
2
5
AD8276
Rg1 40kΩ
-IN
Rg2 40kΩ
Rf1 40kΩ
+
–2
3
+IN
4
-VS
1
REF
6
OUT
5
7
+VS
Rf2 40kΩ
SENSE
R1
R2
Rload
Io
Vref
Vload
Vout
AD8276
Rg1 40kΩ
-IN
Rg2 40kΩ
Rf1 40kΩ
+
–2
3
+IN
4
-VS
1
REF
6
OUT
5
7
+VS
Rf2 40kΩ
SENSE
V+
Io
Vref
5V
AD8276
Rg1 40kΩ
-IN
Rg2 40kΩ
Rf1 40kΩ
+
–2
3
+IN
4
-VS
1
REF
6
OUT
5
7
+VS
Rf2 40kΩ
SENSE
R1
Rload
Vload
Vout
Cost sensitive, ≤15 mA output
Higher accuracy, >15 mA output Higher accuracy, ≤15 mA output
Cost sensitive, >15 mA output

The Generic Instrumentation Amplifier
(In-Amp)
43
~~
COMMON
MODE
VOLTAGE
VCM
+
_
RG
IN-AMP
GAIN = G
VOUTVREF
COMMON MODE ERROR (RTI) =
VCM
CMRR
~
RS/2
RS/2
RS
~
~
VSIG
2
VSIG
2
+
_
+
_

The Three Op Amp In-Amp
VOUT
RG
R1'
R1
R2'
R2
R3'
R3
+
_
+
_
+
_
VREF
VOUT = VSIG • 1 +
2R1
RG
+ VREF
R3
R2
IF R2 = R3, G = 1 +
2R1
RG
CMR 20log
GAIN × 100
% MISMATCH
CMR 20log
GAIN × 100
% MISMATCH
CMR 20log
GAIN × 100
% MISMATCH
~~
~~
~~
VCM
+
_
+
_
VSIG
2
VSIG
2
A1
A2
A3
44

Generalized Bridge Amplifier Using an In-Amp
+VB
+

IN AMP
REF VOUT
RG
+VS
-VSR+R
VB
R
R
VOUT = GAIN
R+R
R–R
R–R
45

1 MΩ
10 nF
10 kΩ
10 kΩ
1 nF
1 nF
100 kΩ
1 µF
AD8495
PCB
Traces
Thermocouple
RFI
Filter
Thermocouple
Amplifier
Filter for
50/60 Hz
Reference
Junction
Measurement
Junction
Common Mode
fc = 16 kHz
Differential
fc = 1.3 kHz
Includes
Reference
Junction
Compensation
fc = 1.6 Hz
5 mV/°C
Ground
Connection
5V
REF
Typical In-Amp Applications
Sensor Interface
 Pressure
 Strain
 Temperature
 Vibration
 Current sensing
Measurement of Biopotentials
 EEG
 ECG
Market Segments
 INI, H/C, PCTL, MIL/AERO,
ATE, AUTO…
46

Different Circuit Topologies to build an In amp
3-Op Amp 2-Op Amp
47
Indirect-Current Feedback Current-Mode Correction
+IN
–IN
OUT
REF
+IN
–IN
OUT
REF
OUT
REF
GM1 GM2
(G-1)R
R
+IN
–IN
+IN
–IN
OUT
REF
2IE
IE
IE = (V – V )/R1
R1
R2
–IN+IN

CMRR vs. Frequency (Different Topologies)
BEST GOOD
48
GOOD BETTER
AD8421
AD8420
AD627
AD8553

Input Common Mode Range in Instrumentation
Amplifiers
Input common-mode voltage
range is limited in
instrumentation amplifiers
 This is not the same as the input
voltage range of each input
 Internal amplifiers may get
saturated in the presence of large
common-mode voltages
 This behavior usually limits single
supply operation at low voltage
levels
The “diamond” plots are a
graphical representation of
these operational limits
 The amplifier will only operate
inside the plot
 Sometimes is necessary to change
the gain, reference voltage or power
supply levels
49

50
Key Features
 Low Power
 115μA
 Industry Leading Gain Accuracy and Drift
 Gain Error: < 50ppm
 Gain Drift: < 0.5ppm/ C
 High CMRR
 CMRR: 110dB @ all gains (DC to 60Hz)
 Wide Input Common Mode Range
 GND – 0.3V to Vs + 0.3V
 Excellent DC Performance
 Input Offset: 60μV
 Offset Drift: 0.2μV/ C
 Other Key Specifications
 Single supply: 1.8V to 5.0V
 Noise RTI: 1.5μVpp (0.1 to10Hz)
 70nV/RtHz @ 1kHz
 Bandwidth: 10kHz @ G=100
 Gain Range: 1-1000
 Input RFI Protection
 Package: 8L MSOP
Applications
 Medical Instrumentation
 Remote Sensing and Hand Held Instrumentation
 Precision Bridge and Current Sense Measurements
 Consumer Peripherals – Gaming, Distributed Computing
Setting the
Gain
–IN
+IN
VREF
R2
R1
G = 1+
R2
R1
AD8237 VOUT
REF
FB
AD8237 - Micro Power, Zero-Drift In Amp

51
300mV operation above and below the supply rails with output swing completely independent of input common-
mode voltage
Industry Leading Input Voltage Range

Single-Supply Data Acquisition System
+2V
+2V  1V
VCM = +2.5V
G = 100
52
AD8237

AD825x Digitally Programmable Gain
Instrumentation Amplifier (PGIA)
AD8250 Gain settings of 1, 2, 5, 10
AD8251 Fine gain setting of 1, 2, 4, 8
AD8253 Coarse gain setting of 1, 10, 100, 1000
Low noise and low offset with 10MHz bandwidth
54
A1 A0DGND WR
AD8253
+VS –VS REF
OUT
+IN
LOGIC
–IN 1
10
8 3
7
4562
9
06983-001

Additional In-Amp Expert Reading
Available Online:
 http://www.analog.com/en/content/cu_dh_designers_guide_to_instrumentation
_amps/fca.html
More Resources Under
 www.analog.com/inamps
55

ADC Driver Amplifiers
Driving ADC inputs
 ADC switching feeds transient back to input pins
 ADC driver amp must reject transients to provide accurate signal
High Performance ADCs
 Recent high performance ADCs have 16 bits and more at 200 MSPS and
higher
 Such performance requires a differential input signal
Differential Amplifiers
 Differential or single-ended input converted to differential output
 Low impedance output stage rejects ADC switching spikes
 Common-mode level set and gain setting allow optimum match to ADC range
Voltage Reference Buffer
 ADC transients can reflect back to reference output
 Op amp buffer with low output impedance at high frequency may be needed
56

Typical Unbuffered Single-Ended Input Transients of
CMOS Switched Capacitor ADC
2.57
Note: Data Taken with 50 Source Resistances
SAMPLING CLOCK

ADC Driver
58
2.4MHz
BPF
FROM
50Ω
SIGNAL
SOURCE
ADA4932-1
VCM VDD1 VDD2 VIO
VOCM
AD8031
AD7626
0.1µF
0.1µF
+5V
+5V +2.5V +2.5V
R3
499Ω
R5
499Ω
R2
53.6Ω
R1
53.6Ω
C1
2.2nF
R4
39Ω
0.1µF
0.1µF
0.1µF
R7
499Ω
R6
499Ω
+2.048V
1
5 6 7 8
–FB
2
9
+IN
3 –IN
4 +FB
16 15 14 13
+7.25V
–2.5V
+VS
–VS
–OUT
+OUT
PAD
R8
33Ω
R9
33Ω
11
10
C5
56pF
C6
56pF
IN–
IN+
0V TO
+4.096V
+4.096V
TO 0V
GND
0.1µF 0.1µF 0.1µF
ADA4932 differential output drives differential input of 16-bit 10 MSPS AD7626
ADC

AD8475:
Differential Funnel Amp and ADC Driver
 Key Features
 Active precision attenuation
 (0.4x or 0.8x)
 Level-translating
 VOCM pin sets output common
mode
 Single-ended to differential conversion
 Differential rail-to-rail output
 Input range beyond the rail
 Key Specifications
 150 MHz bandwidth
 10 nV/√Hz output noise
 50 V/μS slew rate
 –112 dB THD + N
 1 ppm/°C max gain drift
 500 μV max output offset
 3 mA supply current
59
Benefits
 Connect industrial sensors to high
precision differential ADCs
 Simplify design
 Enable quick development
 Reduce PCB size
 Reduce cost
Applications
 Process control modules
 Data acquisition systems
 Medical monitoring devices
 ADC driver
Low Voltage
ADC Inputs
Large
Input
Signal

AD8475: Funnel Amplifier + ADC Driver
AD8475 AD7982
REF
+5V
10kΩ
10kΩ
+IN 0.4x
-IN 0.4x
VOCM
+5V
+IN
-IN
20Ω
20Ω
270pF
270pF
1.35nF
0.5V – 4.5V
VOUT(DIFF) ±4V
0.1µF
4V 2.5V
0.5V – 4.5V
VOUT(DIFF) ±4V
4V 2.5V
SNR=97dB
THD=-113dB
ADR435
0V±10V
60
 Interface ±10 V or ±5 V signal on a
single-supply amplifier
 Integrate 4 Steps in 1
 Attenuate
 Single-ended-to-differential conversion
 Level-shift
 Drive ADC
 Drive differential 18-bit SAR ADC
up to 4 MSPS with few external
components

Precision, Low Power, Single-Supply, Fully
Integrated Differential ADC Driver for Industrial-Level
Signals (CN0180)
61
 Interface ±10 V or ±5 V signal on a
single-supply amplifier
 Integrate 4 Steps in 1
 Attenuate
 Single-ended-to-differential conversion
 Level-shift
 Drive ADC
 Drive differential 18-bit SAR ADC
up to 4 MSPS with few external
components

ADC Driver for High Speed ADCs
100 MSPS 12-Bit ADC
62

ADR45xx – Ultrahigh Precision, Low Noise,
Voltage Reference Product Overview
Key Features
 Ultrahigh accuracy
 Voltage drift: 2 ppm/°C max., B grade
• 5 ppm/°C max., A grade
 Low initial output voltage error: 0.02% max.
 Long-term drift: 25 ppm/1,000 hours typ.
 Excellent noise performance
 1/f noise: <0.5 ppm,pp (0.1 Hz to 10 Hz)
 Wideband noise: <5 μV rms (10 Hz to 10 kHz)
 Versatility
 Input voltage range: 3 V to 15 V
 Low dropout: 200 mV for +2 mA at +125°C
• 1 V for ADR4520, 0.5 V for ADR4525
 Output drive: ±10 mA – no buffer amp needed
 Quiescent current: 800 µA max
 Wide temperature range
 -40oC to +125oC operation
Applications
 Medical/industrial/test instrumentation
 Automotive hybrid battery monitoring
63
Package Temp Price
8-lead SOIC
–40 C to
+125 C
$2.45 @ 1k (A)
$3.45 @ 1k (B)
All Options of the ADR45xx Family
ADR4520 2.048 V Samples
ADR4525 2.5 V Now
ADR4530 3.0 V
ADR4533 3.3 V RTS
ADR4540 4.096 V Mar 2012
ADR4550 5.0 V

Benefits of Precision Current Sensing
Precision Current Sensing allows for finer/more adjustments in
Automotive Control applications
 Automatic Transmission: Larger number of gear options and smoother shifting
 Diesel Injection: Better mileage, lower emissions, reduced noise
 Electric Power Steering: Facilitates transition from Hydraulic to Electro-
Hydraulic
 Electric Motor: enables higher performance systems
 Brake-by-wire and Electric Parking Brake
 Adaptive Suspension
 Advanced Wiper / Memory Seat / One-Touch Down Window
In General, High-side current sensing allows for:
• Lower cost wiring
• Improved diagnostics capabilities
• Precise current sensing
• Improved system efficiencies
64

High-Side vs. Low-Side Current Sensing
65
+
-

High-Side vs. Low-Side Current Sensing
66

67
Typical
Applications
DC-DC CONVERTERS
BANDWIDTH
CMRR over frequency
Response time
POWER SUPPLY
MONITORING
Common Mode Range
Gain value
Response time
VALVE/SOLENOID CONTROL
TEMPERATURE DRIFT
Common mode rejection
Averaging function
MOTOR CONTROL
BIDIRECTIONAL SENSE
TEMPERATURE DRIFT
Output linearity to 0V input
Response time
SOLAR PANEL MONITORING
Inverter / Power Maximizing
Common Mode Range
Gain value
Response time
POWER AMPLIFERS
TEMPERATURE DRIFT

AD8210 – Application Examples
14V
To
control
circuitry
DC Motor Control DC/DC Converter42V
Shunt
ECU
V Out
G=20
Vs
AD8210
V Ref 2
V Ref 1
- IN+ IN
GND
Reference
5V
V Out
G=20
Vs
AD8210
V Ref 2
V Ref 1
- IN+ IN
GND
V Battery
Motor Control Applications
 Industrial DC Motor Control
 Medical Imaging Machine Motor Control
 Automotive DC Motor and Solenoid Control
DC/DC Converter Applications
 Power Supply
 Base Station
 Battery Charging
 Automotive Battery Charging
68

High Common-Mode Current Sensing
Using the AD629 Difference Amplifier
VCM = 270V for VS = 15V
69
Next generation AD8479 with 600V common mode range coming soon

[Circuit board pic here]
Current Monitor with 500 V Common-Mode
Voltage (CN0218)
Circuit Features
 500 V common mode
 0.2% accuracy
Circuit Benefits
 Minimal loading
 Fast response
Inputs
 Power shunt resistor
70
Target Applications Key Parts Used Interface/Connectivity
Metering and Energy
Monitoring
Motor and Power
Control
Power Supplies
AD8212
AD8605
AD7171
ADuM5402
Isolated
SPI

Amplifiers Improve What We See…
The clarity and contrast in this ultrasound comes from the very low
noise floor of the VGA, the constancy of the noise over the entire gain
range, and the very tight delay variance.
AD8332
71

…. And How We Live!
Did you see an accident today?
ADF4158
Xmit Channel
Sig. Generator
PA
AD8283
Rx Channel
Signal Pxing
DSP
ANTENNA
ADAS systems require multi-channel radar receivers, with finely controlled
gain and low channel crosstalk, at very low noise and power factors.
By offering these, AD8283 AFE makes it possible to eliminate most accidents
at speeds less than 25 mph.
72

Downloadable Multisim SPICE
75

Tweet it out! @ADI_News #ADIDC13
What We Covered
Op amps are very versatile devices that can be set up for many
applications
Op amps cannot amplify an input signal with a higher gain than their
own noise – pick low noise op amps
Specialty amplifiers are built-up combinations of op amps with
performance tailored to applications
High performance ADCs need high performance driver amplifiers to
obtain full accuracy
Differential amplifiers can pick off small signals from very high
common-mode voltages
New software and online design tools greatly simplify product
selection and system design
76

Design Resources Covered in this Session
Design Tools & Resources:
Ask technical questions and exchange ideas online in our
EngineerZone™ Support Community
 Choose a technology area from the homepage:
 ez.analog.com
 Access the Design Conference community here:
 www.analog.com/DC13community
77
Name Description URL
ADIsimOpamp On-line tool to select and configure op amps http://designtools.analog.
com/dtAPETWeb/dtAPET
Main.aspx
Diff Amp Calculator On-line tool to design differential amp circuits http://www.analog.com/en
/amplifier-linear-tools/adi-
diff-amp-calc/topic.html
Multisim SPICE Downloadable general purpose SPICE simulator http://www.analog.com/en
/amplifier-linear-
tools/multisim/topic.html

[Circuit board pic here]
Visit the Current Monitor with 500 V Common-
Mode Voltage in the Exhibition Room
Circuit Features
 500 V common mode
 0.2% accuracy
Circuit Benefits
 Minimal loading
 Fast response
Inputs
 Power shunt resistor
78
Target Applications Key Parts Used Interface/Connectivity
Metering and Energy
Monitoring
Motor and Power Control
AD8212
AD8605
AD7171
ADuM5402
Isolated
SPI
This demo board is available for purchase:
www.analog.com/DC13-hardware

Visit the Weigh Scale Demo in the Exhibition
Room
79
Measure weights from
0.1 g to 2000 g
This demo board is available for purchase:
www.analog.com/DC13-hardware
SOFTWARE OUTPUT DISPLAY
EVAL-CN0216-SDPZ
SDP BOARD

Amplifiers: Capture Signals and Drive Precision Systems (Design Conference 2013)

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