amplifiers: capture signals and drive precision systems (design conference 2013)
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Amplifiers: Capture Signals and Drive Precision SystemsAdvanced Techniques of Higher Performance Signal Processing
2
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3
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
4
Analog to Electronic Signal Processing
SENSOR(INPUT)
DIGITAL PROCESSOR
AMP CONVERTER
ACTUATOR(OUTPUT)
AMP CONVERTER
5
Analog to Electronic Signal Processing
SENSOR(INPUT)
DIGITALPROCESSOR
AMP CONVERTER
ACTUATOR(OUTPUT)
AMP CONVERTER
6
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
7
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
8
Original Vacuum-Tube Op Amp from Philbrick Research in 1953: It Used ±300 V Supplies
9
AD823 JFET Input Op Amp Simplified Schematic
INPUTS
+VS
-VS
Q57A=19
Q44A=1
Q43
Q58
Q62
R44
S1NS1P
VB
Q49Q61Q72J6J1
Q48
Q35Q53
I1 Q56
Q59A=1
Q17A=19
OUTPUTQ60
R28
(-)
(+)
VBE + 0.3V
BIAS CURRENT = 25pA MAX @ +25°CINPUT OFFSET VOLTAGE = 0.8mV MAX @ +25°CINPUT VOLTAGE NOISE = 15nV/HzINPUT CURRENT NOISE = 1fA/Hz
10
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
11
Standard Configurations
Non-Inverting R1
+ -
R2
VIN
VOUT
V1I1
Vin
11R
VI
in 21 II
)(
0
1
2
21
R
RVV
RR
VV
inout
inout
;
1
11R
VI 1VVin
)1(1
21
21
11
R
RVV
RR
VVV
out
out
;
I2
Inverting
+ -
R1
R2
VIN
VOUT
Vin
I1
Virtual Ground Because +VIN = -VIN
12
Op Amp Error Sources
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)
13
AN “IDEAL” NON-INVERTING AMPLIFIER
+ -
VinVout
I1
R1
R2
V1
Vid
1VVV idin
outVRR
RV *
21
11
))(1(1
2
idinout VVR
RV
14
DC + AC Errors of a Circuit
PSRR
Vs
CMRR
Ven
A
VRIVV
icm
vo
outsBosid
*
)(1
idinout VVV
))*((1
PSRR
Vs
CMRR
Ven
A
VRIVVV
cm
vo
outsBosinout
0_ vGAINLOOP A
Since en gets multiplied by 1
we get the name “noise gain”
+ -
R
2
Rs VoutVid
Vin
15
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
R2R2
R1
IN
Signal Gain = 1 + R2/R1
Noise Gain = 1 + R2/R1
Signal Gain = - 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, thusbetter stability, worse noise, and higher output offset voltage.
IN
A B C
R1
R2 IN
R1
R2R2
R1
IN
Signal Gain = 1 + R2/R1
Noise Gain = 1 + R2/R1
Signal Gain = R2/R1
Noise Gain = 1 + R2/R1
Signal Gain =
Noise Gain = 1 + R2
+
-
IN +
-
+
-
A B C
R1
R2 IN
R1
R2R2
R1
IN
Signal Gain = 1 + R2/R1
Noise Gain = 1 + R2/R1
Signal Gain = - R2/R1
Noise Gain = 1 + R2/R1
Signal Gain = - R2/R1
Noise Gain = 1 + R2
R1 R3
IN
A B C
R1
R2 IN
R1
R2R2
R1
IN
Signal Gain = 1 + R2/R1
Noise Gain = 1 + R2/R1
Signal Gain = R2/R1
Noise Gain = 1 + R2/R1
Signal Gain =
Noise Gain = 1 + R2
+
-
IN +
-
+
-
A B C
R1
R2 IN
R1
R2R2
R1
IN
Signal Gain = 1 + R2/R1
Noise Gain = 1 + R2/R1
Signal Gain = - 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, thusbetter stability, worse noise, and higher output offset voltage.
IN
A B C
R1
R2 IN
R1
R2R2
R1
IN
Signal Gain = 1 + R2/R1
Noise Gain = 1 + R2/R1
Signal Gain = R2/R1
Noise Gain = 1 + R2/R1
Signal Gain =
Noise Gain = 1 + R2
+
-
IN +
-
+
-
A B C
R1
R2 IN
R1
R2R2
R1
IN
Signal Gain = 1 + R2/R1
Noise Gain = 1 + R2/R1
Signal Gain = - R2/R1
Noise Gain = 1 + R2/R1
Signal Gain = - R2/R1
Noise Gain = 1 + R2
R1 R3
IN
A B C
R1
R2 IN
R1
R2R2
R1
IN
Signal Gain = 1 + R2/R1
Noise Gain = 1 + R2/R1
Signal Gain = R2/R1
Noise Gain = 1 + R2/R1
Signal Gain =
Noise Gain = 1 + R2
16
Total Noise Calculation
FCL = CLOSED LOOP BANDWIDTH
R1
VON
Rp
In-
In+
R2
Vn
VR2J
VR1J
VRPJ
+
= BW [(In-2)R22] [NG] + [(In+2)RP
2] [NG] + VN2 [NG] + 4kTR2 [NG-1] + 4kTR1 [NG-1] + 4kTRP [NG]VON
BW = 1.57 FCL
FCL = CLOSED LOOP BANDWIDTH
R1
VON
Rp
In-
In+
R2
Vn
VR2J
VR1J
VRPJ
+
R1
VON
Rp
In-
In+
R2
Vn
VR2J
VR1J
VRPJ
+
= BW [(In-2)R22] [NG] + [(In+2)RP
2] [NG] + VN2 [NG] + 4kTR2 [NG-1] + 4kTR1 [NG-1] + 4kTRP [NG]VON = BW [(In-2)R2
2] [NG] + [(In+2)RP2] [NG] + VN
2 [NG] + 4kTR2 [NG-1] + 4kTR1 [NG-1] + 4kTRP [NG]VON
BW = 1.57 FCL
17
Dominant Noise Source Determined by Input Impedance
CONTRIBUTIONFROM
AMPLIFIERVOLTAGE NOISE
AMPLIFIERCURRENT NOISE
FLOWING IN R
JOHNSONNOISE 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: OP27Voltage Noise = 3nV / HzCurrent Noise = 1pA / HzT = 25°C
OP27
R2R1
Neglect R1 and R2Noise Contribution
CONTRIBUTIONFROM
AMPLIFIERVOLTAGE NOISE
AMPLIFIERCURRENT NOISE
FLOWING IN R
JOHNSONNOISE 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: OP27Voltage Noise = 3nV / HzCurrent Noise = 1pA / HzT = 25°C
OP27
R2R1
Neglect R1 and R2Noise Contribution
AD8675
AD8675
18
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
CORNER1f
NOISEnV / Hz
orHz
en, in
k
FC
k FC1f
en, in =3dB/Octave
WHITE NOISE
LOG f
CORNER1f
NOISEnV / Hz
orpA / Hz
en, in
k
FC
k FC1f
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
CORNER1f
NOISEnV / Hz
orHz
en, in
k
FC
k FC1f
en, in =3dB/Octave
WHITE NOISE
LOG f
CORNER1f
NOISEnV / Hz
orpA / Hz
en, in
k
FC
k FC1f
en, in =
19
The Peak-to-Peak Noise in the 0.1 Hz to 10 Hz Bandwidth ADA4528
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
aNo 1/f Noise
5.6nV/Hz
ADI AdvantagesWorld’s Most Accurate Op Amp, Lowest Voltage Noise Zero-
Drift Op Amp
21
Precision Weigh Scale Design Using the AD7791 24-Bit Sigma-Delta ADC with External ADA4528-1 Zero-Drift Amplifiers (CN0216)
24-bit ADC
Noise optimized forDC measurements
1-22
1) More capacitance, more noise peaking2) 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
23
ADI AmplifiersBased 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
24
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
•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
AD8597/91 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
aOUT 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
26
Optimizing AC Performance in an 18-bit, 250 kSPS, PulSAR Measurement Circuit (CN0261)
Noise optimized for Mid-range frequencies
27
Analog to Electronic Signal Processing
SENSOR(INPUT)
DIGITALPROCESSOR
AMP CONVERTER
ACTUATOR(OUTPUT)
AMP CONVERTER
28
20-Bit, Linear, Low Noise, Precision, Bipolar ±10 V DC Voltage Source (CN0191)
1 – ppm resolutionNeeds low noiseIn all components
Without Buffer
29
DNL vs. Code INL vs. Code
30
Using a Rail-to-Rail Input Amplifier
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
32
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
33
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
Integrated “Amplifier” Products
34
2k2k
ZV
YYXX
10
)21()21(
Current Sense
DifferenceAmps
InstrumentationAmplifiers
VGAs
MultipliersRMS-DC Converters Thermocouple Amplifiers
5mV/C
T
mRMS dtTT
VV0
2sin1
35
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
36
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
37
Op Amp Subtractor or Difference Amplifier
VOUT = (V2 – V1)R2R1
R1 R2
_
+
V1
V2
VOUT
R1' R2'
R2R1 =
R2'R1'R2'R1' CRITICAL FOR HIGH CMR
0.1% TOTAL MISMATCH YIELDS 66dB CMR FOR R1 = R2
CMR = 20 log10
1 +R2R1
Kr
Where Kr = Total FractionalMismatch of R1/ R2 TOR1'/R2'
EXTREMELY SENSITIVE TO SOURCE IMPEDANCE IMBALANCE
REF
AD8271 : Precision Difference Amplifier with Programmable Gain
38
a
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
07
363
-032
10
9
8
2
3
4
39
AD8270/AD8271 Flexible Gain Configurations
=
07
363
-053
1
7
10kΩ
AD8271
10kΩ
10kΩ
10kΩ
20kΩ
20kΩ
10kΩ
P4
P3
P2
P1+IN
GND OUT
OUT
N1
N2
N310
9
8
2
3
4
–IN
–IN
+IN
5kΩ
5kΩ
10kΩ
10kΩ
=
–IN
+IN
10kΩ
10kΩ
10kΩ
10kΩ
+VS + –VS
2
07
363
-057
1
7
10kΩ
AD8271
10kΩ
10kΩ
10kΩ
20kΩ
20kΩ
10kΩ
P4
P3
P2
P1+IN
NC NC
OUTOUT
N1
N2
N310
9
8
2
3
4
–IN
–VS
+V
=
–IN
+IN
10kΩ
5kΩ
5kΩ
10kΩ
GND
07
36
3-0
55
1
7
10kΩ
AD8271
10kΩ
10kΩ
10kΩ
20kΩ
20kΩ
10kΩ
P4
P3
P2
P1
OUT
OUT
N1
N2
N310
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
40
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
41
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
AD8277A1
–
+
AD8277A2
–
+
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 = 10kΩR4, R5 = 20kΩ
Conventional precision absolute value circuit requires many fast, high precision (i.e., expensive) components, and has performance issues.
42
AD8276/AD8277/AD8278/AD8279 Applications – Building Current Sources (Continued)
R1
R2
Rload
V+
Io
Vref
Vload
Vout
AD8276
Rg1 40kΩ
-INRg2 40kΩ
Rf1 40kΩ
+
–2
3
+IN
4
-VS1
REF
6
OUT
5
7
+VS
Rf2 40kΩ
SENSE
R1
Rload
+V
Io
Vref
Vload
AD8603
+5V
Vout
4 4
31
2
5AD8276
Rg1 40kΩ
-INRg2 40kΩ
Rf1 40kΩ
+
–2
3
+IN
4
-VS1
REF
6
OUT
5
7
+VS
Rf2 40kΩ
SENSE
R1
R2
RloadIo
Vref
Vload
Vout
AD8276
Rg1 40kΩ
-INRg2 40kΩ
Rf1 40kΩ
+
–2
3
+IN
4
-VS1
REF
6
OUT
5
7
+VS
Rf2 40kΩ
SENSE
V+
Io
Vref
5V
AD8276
Rg1 40kΩ
-INRg2 40kΩ
Rf1 40kΩ
+
–2
3
+IN
4
-VS1
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
43
The Generic Instrumentation Amplifier (In-Amp)
~~
COMMONMODE
VOLTAGEVCM
+
_
RG
IN-AMPGAIN = G
VOUTVREF
COMMON MODE ERROR (RTI) =VCM
CMRR
~
RS/2
RS/2
RS
~
~
VSIG2
VSIG2
+
_
+
_
44
The Three Op Amp In-Amp
VOUTRG
R1'
R1
R2'
R2
R3'
R3
+
_
+
_
+
_
VREF
VOUT = VSIG • 1 +2R1RG
+ VREFR3R2
IF R2 = R3, G = 1 +2R1RG
CMR 20logGAIN × 100
% MISMATCHCMR 20log
GAIN × 100% MISMATCH
CMR 20logGAIN × 100
% MISMATCH
~~
~~
~~
VCM
+
_
+
_
VSIG2
VSIG2
A1
A2
A3
45
Generalized Bridge Amplifier Using an In-Amp
+VB
+
-
IN AMP
REF VOUT
RG
+VS
-VSR+DR
VB
DR
RVOUT = GAIN
R+DRR–DR
R–DR
46
1 MΩ
10 nF
10 kΩ
10 kΩ
1 nF
1 nF
100 kΩ
1 µF
AD8495
PCBTraces
Thermocouple
RFIFilter
Thermocouple Amplifier
Filter for50/60 Hz
ReferenceJunction
MeasurementJunction
Common Mode fc = 16 kHz
Differential fc = 1.3 kHz
IncludesReferenceJunction
Compensation
fc = 1.6 Hz
5 mV/°C
GroundConnection
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…
47
Different Circuit Topologies to build an In amp
3-Op Amp 2-Op Amp
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
48
CMRR vs. Frequency (Different Topologies)
BEST GOOD
GOOD BETTER
AD8421
AD8420
AD627
AD8553
49
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
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+ R2R1
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
52
Single-Supply Data Acquisition System
+2V
+2V 1V
VCM = +2.5V
G = 100
AD8237
54
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
A1 A0DGND WR
AD8253
+VS –VS REF
OUT
+IN
LOGIC–IN 1
10
8 3
7
4562
9
55
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
56
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
Typical Unbuffered Single-Ended Input Transients of CMOS Switched Capacitor ADC
2.57
Note: Data Taken with 50 Source Resistances
SAMPLING CLOCK
58
ADC Driver
2.4MHzBPF
FROM50ΩSIGNALSOURCE
ADA4932-1
VCM VDD1 VDD2 VIO
VOCM
AD8031
AD7626
0.1µF
0.1µF
+5V
+5V +2.5V +2.5V
R3499Ω
R5499Ω
R253.6Ω
R153.6Ω
C12.2nFR439Ω
0.1µF
0.1µF
0.1µF
R7499Ω
R6499Ω
+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
R833Ω
R933Ω
11
10
C556pF
C656pF
IN–
IN+
0V TO+4.096V
+4.096VTO 0V
GND
0.1µF 0.1µF 0.1µ
ADA4932 differential output drives differential input of 16-bit 10 MSPS AD7626 ADC
59
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
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 InputSignal
60
AD8475: Funnel Amplifier + ADC Driver
AD8475 AD7982
REF
+5V
10kΩ
10kΩ
+IN 0.4x
-IN 0.4xVOCM
+5V
+IN
-IN
20Ω
20Ω270pF
270pF
1.35nF
0.5V – 4.5VVOUT(DIFF) ±4V
0.1µF
4V 2.5V
0.5V – 4.5VVOUT(DIFF) ±4V
4V 2.5V
SNR=97dBTHD=-113dB
ADR435
0V±10V
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
62
ADC Driver for High Speed ADCs 100 MSPS 12-Bit ADC
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
65
High-Side vs. Low-Side Current Sensing
+
-
66
High-Side vs. Low-Side Current Sensing
67
Typical Applications
DC-DC CONVERTERSBANDWIDTHCMRR over frequencyResponse time
POWER SUPPLY MONITORINGCommon Mode RangeGain valueResponse time
AD8210
VALVE/SOLENOID CONTROLTEMPERATURE DRIFTCommon mode rejectionAveraging function
MOTOR CONTROLBIDIRECTIONAL SENSETEMPERATURE DRIFTCommon mode rejectionOutput linearity to 0V inputResponse time
SOLAR PANEL MONITORINGInverter / Power MaximizingCommon Mode RangeGain valueResponse time
POWER AMPLIFERSTEMPERATURE DRIFTCommon mode rejection
AD8210 – Application Examples
14V
To control circuitry
DC Motor Control DC/DC Converter42V
Shunt
ECU
V OutG=20
Vs
AD8210
V Ref 2
V Ref 1
- IN+ IN
GND
Reference
5V
V OutG=20
Vs
AD8210
V Ref 2
V Ref 1
- IN+ IN
GND
V Battery
Motor Control ApplicationsIndustrial DC Motor ControlMedical Imaging Machine Motor Control Automotive DC Motor and Solenoid Control
DC/DC Converter ApplicationsPower SupplyBase StationBattery ChargingAutomotive Battery Charging
68
69
High Common-Mode Current Sensing Using the AD629 Difference Amplifier
VCM = 270V for VS = 15V
Next generation AD8479 with 600V common mode range coming soon
70
[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
Target Applications Key Parts Used Interface/Connectivity
Metering and Energy MonitoringMotor and Power ControlPower Supplies
AD8212AD8605AD7171ADuM5402
IsolatedSPI
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?
ADF4158Xmit Channel
Sig. Generator
PA
AD8283Rx 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 accidentsat speeds less than 25 mph.
72
73
ADIsimOpAmp
74
ADI Diff-Amp Calculator
75
Downloadable Multisim SPICE
76 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
77
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
Name Description URL
ADIsimOpamp On-line tool to select and configure op amps http://designtools.analog.com/dtAPETWeb/dtAPETMain.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
78 Tweet it out! @ADI_News #ADIDC13
[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
Target Applications Key Parts Used Interface/Connectivity
Metering and Energy MonitoringMotor and Power Control
AD8212AD8605AD7171ADuM5402
IsolatedSPI
This demo board is available for purchase: www.analog.com/DC13-hardware
79 Tweet it out! @ADI_News #ADIDC13
Visit the Weigh Scale Demo in the Exhibition Room
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
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