class 3: the fundamentals of designing with semiconductors
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The World Leader in High Performance Signal Processing Solutions
THE FUNDAMENTALS OF DESIGNING WITH SEMICONDUCTORS FOR SIGNAL
PROCESSING APPLICATIONS
Class 3 - BEYOND THE OP AMP
Presented by David Kress
Analog to Electronic signal processing
Sensor(INPUT)
Digital ProcessorAmp Converter
Actuator(OUTPUT)
Amp Converter
Analog to Electronic signal processing
Sensor(INPUT)
Digital ProcessorAmp Converter
Actuator(OUTPUT)
Amp Converter
Amplifiers and Operational AmplifiersAmplifiers
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
ampsOperational 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
Specialty Amplifiers
Specialty AmplifiersDesigned for a specific signal typeExtract and amplify only the signal of interestPick off a small differential signal from a large common-mode
voltageCapture and demodulate a low-level AC signalCompress a high-dynamic range signalProvide automatic or controlled gain-changingSend and receive precision signalsProvide high-speed low-impedance power outputUse the analog domain to its best advantage to prepare a clean
signal for the data converter
Specialty Amplifier Types
General Inst. Amps. Differential Amps. Current-sense Amps. Programmable gain Demodulating amps (AD630 and AD698) Thermocouple amps Logarithmic amps with time-gain-controlADC drivers Clamp amps Funnel amplifierLine drivers/receivers Isolation amps
Single-ended vs. Differential Signals
Single-ended signalsSignal is measured referred to groundWhen signals are bipolar (+ and-), negative supplies neededAC signals are typically bipolar or need special ‘floating’, or
capacitive couplingGround often carries high noise from other signals or power,
compromising the signalDifferential signals
Both sides of the signal float ‘off ground’Signals are separated from ground and other signalsHigh frequency and accuracy usually need differential handlingCommon mode (average) can be set for single supplySpecialized differential/difference amplifiers are needed
Instrumentation, Difference and Differential Amplifiers Instrumentation amplifiers
Amplify differential inputs to a single-ended outputNormally both amplifier inputs are high impedanceProvide high gain (up to 10,000) and low noiseNormally handle low-level signals from sensors
Difference amplifiersAmplify differential inputs from high common mode voltage levelsOften include input attenuator to allow operation outside suppliesHigh common model rejection even at high frequencies
Differential amplifiersHigh frequency amplifiers with differential input and outputHandle higher-level signals at lower gainsTypically used for line driving/receiving and ADC driving
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
+
_
+
_
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
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
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
AD620B Bridge Amplifier DC Error Budget
+
–
350100mV FSLOAD CELL
AD620B SPECS @ +25°C, ±15V
VOSI + VOSO/G = 55µV maxIOS = 0.5nA maxGain Error = 0.15%Gain Nonlinearity = 40ppm0.1Hz to 10Hz Noise = 280nVp-pCMR = 120dB @ 60Hz
VOS
IOS
Gain Error
Gain Nonlinearity
CMR Error
0.1Hz to 10Hz 1/f Noise
TotalUnadjusted
Error
ResolutionError
55µV ÷ 100mV
350 × 0.5nA ÷ 100mV
0.15%
40ppm
120dB 1ppm × 5V ÷ 100mV
280nV ÷ 100mV
9 Bits Accurate
14 Bits Accurate
550ppm
1.8ppm
1500ppm
40ppm
50ppm
2.8ppm
2145ppm
42.8ppm
MAXIMUM ERROR CONTRIBUTION, +25°CFULLSCALE: VIN = 100mV, VOUT = 10V
+10V
AD620B
REF
499
RG
G = 100
VCM = 5V
SINGLE-SUPPLY DATA ACQUISITION SYSTEM
+2V
+2V 1V
VCM = +2.5V
G = 100
High Common-Mode Current Sensing Using the AD629 Difference Amplifier
VCM = 270V for VS = 15V
AD8253
AD8251/53 Digitally Programmable Gain Instrumentation Amplifier (PGIA)
A1 A0DGND WR
AD8253
+VS –VS REF
OUT
+IN
LOGIC–IN 1
10
8 3
7
4562
9
-IN
+IN
A1A2
REF
OUT
+
-
Gain Logic
A1
A2
A3
+VS
-VS
AD8251
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
Demodulating Amplifiers
AC demodulationLow-level low-frequency AC signal processing can be used for
capturing low-level signalsA modulated signal bypasses issues of offset and noise in
amplifiersUseful for transformer-coupled position detectorsLock-in amplifier can find narrow band signal 100db below the
interfering noise
IMPROVED LVDT OUTPUT SIGNAL PROCESSING
~AC
SOURCE
+ ABSOLUTEVALUE
ABSOLUTEVALUE
FILTER
FILTER
+
_
VOUT
_
POSITION +_
VOUT+
_
LVDT
Lock-in Amplifier
A
B
10k
100R
C OUTPUT
LOW-PASSFILTER
A
B
C
R
100RAD630
10k
5k
2.5k
2.5k
20
1917
1
16
AD54213
AD542
14
10
9
CLIPPEDBAND-LIMITEDWHITENOISE
100dBATTENUATION
0.1HzMODULATED
400HzCARRIER
CARRIERPHASEREFERENCE
1
AD630 demodulates 400Hz signal 100dB below noise
Thermocouple Amplifiers
Cold junction compensationThermocouples use two different metals that develop a voltage
varying with temperatureThe temperature effect also occurs at the point where the
thermocouple wires connect to the instrumentThis ‘cold junction’ effect must be compensated for to get
accurate measurementsVarious techniques have been used including ice bathsModern thermocouple amplifiers include accurate compensation
circuitry
Using a Temperature Sensor for Cold-Junction Compensations
TEMPERATURECOMPENSATION
CIRCUIT
TEMPSENSOR
T2V(T2)T1 V(T1)
V(OUT)
V(COMP)
SAMETEMP
METAL A
METAL B
METAL A
COPPERCOPPER
ISOTHERMAL BLOCKV(COMP) = f(T2)
V(OUT) = V(T1) – V(T2) + V(COMP)
IF V(COMP) = V(T2) – V(0°C), THEN
V(OUT) = V(T1) – V(0°C)
TEMPERATURECOMPENSATION
CIRCUIT
TEMPSENSOR
T2V(T2)T1 V(T1)
V(OUT)
V(COMP)
SAMETEMP
METAL A
METAL B
METAL A
COPPERCOPPER
ISOTHERMAL BLOCKV(COMP) = f(T2)
V(OUT) = V(T1) – V(T2) + V(COMP)
IF V(COMP) = V(T2) – V(0°C), THEN
V(OUT) = V(T1) – V(0°C)
AD594/AD595 Monolithic Thermocouple Amplifier with Cold-Junction Compensation
ICEPOINTCOMP
+
OVERLOADDETECT
VOUT10mV/°C
+5V
BROKENTHERMOCOUPLE
ALARM
4.7k
G
+
–TC––
+TC+
+ATHERMOCOUPLE
G
AD594/AD595
TYPE J: AD594TYPE K: AD595
0.1µF
ICEPOINTCOMP
+
OVERLOADDETECT
VOUT10mV/°C
+5V
BROKENTHERMOCOUPLE
ALARM
4.7k
G
+
–TC––
+TC+
+ATHERMOCOUPLE
G
AD594/AD595
TYPE J: AD594TYPE K: AD595
0.1µF
Log Amplifiers
Signal compressionMany applications must capture signals over a very wide dynamic
rangeRadio antennas capturing broadcast signalsPhotomultipliers and photodiodes capture light signals over a very
wide rangeTo process and use these signals, they need to be compressed to
a much smaller rangeLogarithmic amplifiers
Log amplifiers compress signals over ranges of as much as 120db – a million to one -- to a normal range of 1 to 10 volts
Accuracy is typically 0.1 to 0.5 dB -- 1 to 5%
Log Amp Transfer Function
IDEAL
ACTUAL
SLOPE = VY
2VY
VY
IDEAL
ACTUAL
VYLOG (VIN/VX)
+
-VIN=VX
VIN=10VX VIN=100VXINPUT ONLOG SCALE
VOUT = VY log10
0
VIN
VX
IDEAL
ACTUAL
SLOPE = VY
2VY
VY
IDEAL
ACTUAL
VYLOG (VIN/VX)
+
-VIN=VX
VIN=10VX VIN=100VXINPUT ONLOG SCALE
VOUT = VY log10
0
VIN
VX
Log Amplifier Accuracy
5
4
3
2
1
–4
–5
500MHz
100MHz
10MHz
–3
–2
–1
0
–80 –70 –60 –50 –40 –30 –20 –10 0 10 20
ER
RO
R(d
B)
INPUT LEVEL (dBm)
AD8307 covers 80dB with 0.5dB accuracy
AD8307 six-decade RF power measurement
TOANTENNA
VP
604Ω
100kΩ1/2W
NC
2kΩ
VR12kΩ
INT ±3dB
51pF
51pF
0.1µF
NC
OUTPUT
LEAD-THROUGH
CAPACITORS,1nF
1nF
NC = NO CONNECT
+5V
VOUT
AD8307INP VPS ENB INT
INM COM OFS OUT
8 7 6 5
2 3 41
50Ω INPUTFROM P.A.
1µW TO1kW
22Ω
Time-gain-control with AD8335
BEAMFORMERCENTRAL CONTROL
Rx BEAMFORMER(B AND F MODES)
COLORDOPPLER (PW)PROCESSING
(F MODE)
IMAGE ANDMOTION
PROCESSING(B MODE)
SPECTRALDOPPLER
PROCESSINGMODE
DISPLAYAUDIOOUTPUT
TX BEAMFORMER
CW (ANALOG)BEAMFORMER
LNAs
TRANSDUCERARRAY
128, 256 ETC.ELEMENTS
BIDIRECTIONALCABLE
HVMUX/
DEMUX
T/RSWITCHES
TX HV AMPs
MULTICHANNELTGC USES MANY VGAs
TGCTIME GAIN COMPENSATION
VGAsAD8335
Ultrasound processor changes AD8335 gain to account for changes in signal strength with tissue depth
ADC driver amplifiers
High performance ADCsRecent high performance ADCs have 16-bits and more at 200MSPS
and higherSuch performance requires a differential input signal
Differential amplifiersDifferential or single-ended input converted to differential outputLow impedance output stage rejects ADC switching spikesCommon mode level set and gain setting allow optimum match to
ADC range
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 10MSPS AD7626 ADC
ADC Input Clamp Amplifiers
Imaging systemsUltrasound and imaging systems often exhibit high-level
transients in practiceInput signals can easily exceed supply and ADC input rangeLong recovery times can impair image stability
Clamp amplifiersClamp amplifiers capture and suppress input transientsAmplifier output does not exceed ADC rangeTransient recovery takes a few nanoseconds
AD8036/AD8037 Clamp Amplifier Equivalent Circuit
+
-A1
RF
140
VOUT
-VIN
+VIN
VH
+1
+1
+1
+
-
+
-
CH
CL
VL
A
B
C
S1
A2+1
S1 A B C
VIN > VH 0 1 0
VL VIN VH 1 0 0
VIN < VL 0 0 1
Comparison of Input and Output Clamping
AD8475: Differential Funnel Amp & ADC DriverKEY 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 -112dB 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 ADC’s 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
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 ±10V or ±5V 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 4MSPS with few external components
AD8475 : Funnel Amplifier + ADC Driver
Balanced Audio Transmission System
Video Difference Amplifier with Variable Common
GM
VP
VOUT
INPUTCOMMON
VN
0.1µF
AD8301
2
3
4
8
7
6
5
A = 1
C
0.1µF
INPUTSIGNAL
V1
V2
OUTPUTCOMMON
V3VOUT = V1 – V2 + V3
AD830 allows different input and output common mode voltage for matching ADC input range
APPLICATIONS FOR ISOLATION AMPLIFIERS
Sensor is at a High Potential Relative to Other Circuitry(or may become so under Fault Conditions)
Sensor May Not Carry Dangerous Voltages, Irrespective of Faults in Other Circuitry(e.g. Patient Monitoring and Intrinsically Safe Equipment for use with Explosive Gases)
To Break Ground Loops
AD210 3-PORT ISOLATION AMPLIFIER
MODDEMODFILTER+
_ _
+
INPUTPOWERSUPPLY
OUTPUTPOWERSUPPLY
POWEROSCILLATOR
T1
T2 T3
INPUT OUTPUT
POWER
FB
–IN
+IN
ICOM
+VISS
–VISS
PWR PWR COM
VO
OCOM
+VOSS
–VOSS
AD210 ISOLATION AMPLIFIER KEY FEATURES
Transformer Coupled
High Common Mode Voltage Isolation:
2500V RMS Continuous
±3500V Peak Continuous
Wide Bandwidth: 20kHz (Full Power)
0.012% Maximum Linearity Error
Input Amplifier: Gain 1 to 100
Isolated Input and Output Power Supplies,
±15V, ±5mA
MOTOR CONTROL CURRENT SENSING
MODDEMODFILTER+
_ _
+
INPUTPOWERSUPPLY
OUTPUTPOWERSUPPLY
POWEROSCILLATOR
T1
T2 T3
INPUT OUTPUT
POWER
FB
–IN
+IN
ICOM
+VISS
–VISS
PWR PWR COM
VO
OCOM
+VOSS
–VOSS
REF
+15V
–15V
HIGH VOLAGEAC INPUT < 2500V RMS
M
RG0.01W AD620
AD210
+15V
+
_
RG = 499W
FOR G = 100
OUTPUT
Fundamentals Webcasts 2011
January Introduction and Fundamentals of Sensors February The Op Amp March Beyond the Op Amp April Converters, Part 1, Understanding Sampled Data Systems May Converters, Part 2, Digital-to-Analog Converters June Converters, Part 3, Analog-to-Digital Converters July Powering your circuit August RF: Making your circuit mobile September Fundamentals of DSP/Embedded System design October Challenges in Industrial Design November Tips and Tricks for laying out your PC board December Final Exam, Ask Analog Devices
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