Beyond the Op Amp

1. 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

2. Analog to Electronic signal processing
Sensor Amp Converter Digital Processor
(INPUT)
Actuator Amp Converter
(OUTPUT)

3. Analog to Electronic signal processing
Sensor Amp Converter Digital Processor
(INPUT)
Actuator Amp Converter
(OUTPUT)

4. 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

5. 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

6. 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-control
 ADC drivers
 Clamp amps
 Funnel amplifier
 Line drivers/receivers
 Isolation amps

7. Single-ended vs. Differential Signals
 Single-ended signals
 Signalis 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

8. 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 model 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

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

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

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

12. GENERALIZED BRIDGE AMPLIFIER USING
AN IN-AMP
VB
R+R +VS
R–R R
VOUT = VB GAIN
R
-
RG IN AMP
REF VOUT
+
R–R
R+R -VS

13. AD620B Bridge Amplifier DC Error Budget
+10V 499 MAXIMUM ERROR CONTRIBUTION, +25°C
VCM = 5V FULLSCALE: VIN = 100mV, VOUT = 10V
RG
+ VOS 55µV ÷ 100mV 550ppm
AD620B IOS 350 × 0.5nA ÷ 100mV 1.8ppm
Gain Error 0.15% 1500ppm
– REF
Gain 40ppm 40ppm
G = 100
Nonlinearity
350100mV FS
LOAD CELL CMR Error 120dB
1ppm × 5V ÷ 100mV 50ppm
AD620B SPECS @ +25°C, ±15V 0.1Hz to 10Hz
280nV ÷ 100mV 2.8ppm
VOSI + VOSO/G = 55µV max 1/f Noise
IOS = 0.5nA max
Total
Gain Error = 0.15% Unadjusted  9 Bits Accurate 2145ppm
Gain Nonlinearity = 40ppm Error
0.1Hz to 10Hz Noise = 280nVp-p
Resolution  14 Bits Accurate 42.8ppm
CMR = 120dB @ 60Hz
Error

14. SINGLE-SUPPLY DATA ACQUISITION
SYSTEM
+2V  1V
VCM = +2.5V
G = 100
+2V

15. High Common-Mode Current Sensing
Using the AD629 Difference Amplifier
VCM = 270V for VS = 15V

16. AD8251/53 Digitally Programmable Gain
Instrumentation Amplifier (PGIA)
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
+VS DGND WR A1 A0
2 6 5 4
-IN
LOGIC
–IN 1
A1
-
7 OUT
A1 Gain Logic A3 OUT
A2
+
+IN 10
A2
+IN
AD8253
06983-001
8 3 9
-VS REF +VS –VS REF
AD8251 AD8253

17. Demodulating Amplifiers
 AC demodulation
 Low-level low-frequency AC signal processing can be used for
capturing low-level signals
 A modulated signal bypasses issues of offset and noise in
amplifiers
 Useful for transformer-coupled position detectors
 Lock-in amplifier can find narrow band signal 100db below the
interfering noise

18. IMPROVED LVDT OUTPUT SIGNAL
PROCESSING
ABSOLUTE
+ FILTER
VALUE
+ VOUT
AC
~ _
SOURCE
ABSOLUTE
_ FILTER
VALUE
LVDT
+ VOUT
_ POSITION +
_

19. Lock-in Amplifier
AD630 demodulates 400Hz signal 100dB below noise
CLIPPED
C
BAND-LIMITED
WHITENOISE AD630
B 16 5k
100R
15 10k
AD542
1 2.5k AD542
20 A 13 R
19
17 2.5k B
100dB 100R
ATTENUATION 14 10k
C OUTPUT
A
10 LOW-PASS
0.1Hz 9 FILTER
MODULATED
400Hz CARRIER
CARRIER PHASE
REFERENCE

20. Thermocouple Amplifiers
 Cold junction compensation
 Thermocouples use two different metals that develop a voltage
varying with temperature
 The temperature effect also occurs at the point where the
thermocouple wires connect to the instrument
 This ‘cold junction’ effect must be compensated for to get accurate
measurements
 Various techniques have been used including ice baths
 Modern thermocouple amplifiers include accurate compensation
circuitry

21. Using a Temperature Sensor for Cold-
Junction Compensations
V(OUT) TEMPERATURE
V(COMP) COMPENSATION
CIRCUIT
COPPER COPPER
METAL A SAME METAL A
TEMP TEMP
SENSOR
T1 V(T1) V(T2) T2
METAL B
V(COMP) = f(T2)
ISOTHERMAL BLOCK
V(OUT) = V(T1) – V(T2) + V(COMP)
IF V(COMP) = V(T2) – V(0°C), THEN
V(OUT) = V(T1) – V(0°C)

22. AD594/AD595 Monolithic Thermocouple
Amplifier with Cold-Junction Compensation
+5V
0.1µF BROKEN
4.7k THERMOCOUPLE VOUT
ALARM 10mV/°C
OVERLOAD
TYPE J: AD594 DETECT
TYPE K: AD595
THERMOCOUPLE AD594/AD595 +A
– – –TC
ICE
G + G POINT
+ + COMP
+TC

23. Log Amplifiers
 Signal compression
 Many applications must capture signals over a very wide dynamic
range
 Radio antennas capturing broadcast signals
 Photomultipliers and photodiodes capture light signals over a very
wide range
 To process and use these signals, they need to be compressed to
a much smaller range
 Logarithmic 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%

24. Log Amp Transfer Function
VYLOG (VIN/VX)
IDEAL
ACTUAL
2VY
SLOPE = VY
VY VIN
VOUT = VY log10
VX
+
0
ACTUAL VIN=10VX VIN=100VX INPUT ON
VIN=VX
- IDEAL LOG SCALE

25. Log Amplifier Accuracy
AD8307 covers 80dB with 0.5dB accuracy
5
4
3 500MHz
2
ERROR (dB)
1
0
10MHz
–1
100MHz
–2
–3
–4
–5
–80 –70 –60 –50 –40 –30 –20 –10 0 10 20
INPUT LEVEL (dBm)

26. AD8307 six-decade RF power
measurement
TO
ANTENNA
100kΩ 0.1µF
1/2W VP
22Ω
51pF +5V
NC
8 7 6 5
VR1 LEAD-
INP VPS ENB INT THROUGH
2kΩ
AD8307 CAPACITORS,
INT ±3dB
1nF
50Ω INPUT INM COM OFS OUT
FROM P.A. 604Ω
1 2 3 4
1µW TO 2kΩ
1kW NC VOUT
51pF 1nF OUTPUT
NC = NO CONNECT

27. Time-gain-control with AD8335
Ultrasound processor changes AD8335 gain to account
for changes in signal strength with tissue depth
TX HV AMPs
TX BEAMFORMER BEAMFORMER
CENTRAL CONTROL
MULTICHANNEL
TGC USES MANY VGAs
HV
AD8335 VGAs
T/R Rx BEAMFORMER
MUX/ SWITCHES LNAs
DEMUX (B AND F MODES)
TRANSDUCER TGC
ARRAY TIME GAIN COMPENSATION
128, 256 ETC.
ELEMENTS CW (ANALOG)
BIDIRECTIONAL BEAMFORMER SPECTRAL IMAGE AND COLOR
CABLE DOPPLER MOTION DOPPLER (PW)
PROCESSING PROCESSING PROCESSING
MODE (B MODE) (F MODE)
AUDIO DISPLAY
OUTPUT

28. ADC driver amplifiers
 High performance ADCs
 Recent high performance ADCs have 16-bits and more at 200MSPS
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

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

30. ADC Input Clamp Amplifiers
 Imaging systems
 Ultrasound and imaging systems often exhibit high-level
transients in practice
 Input signals can easily exceed supply and ADC input range
 Long recovery times can impair image stability
 Clamp amplifiers
 Clamp amplifiers capture and suppress input transients
 Amplifier output does not exceed ADC range
 Transient recovery takes a few nanoseconds

31. AD8036/AD8037 Clamp Amplifier Equivalent
Circuit
RF
14 0 
-V IN +
A1 A2 VOUT
A - +1
+VIN +1
S1
VH B
+1
VL C S1 A B C
+1
V IN > V H 0 1 0
+
CH V L  V IN  V H 1 0 0
-
V IN < V L 0 0 1
+
CL
-

32. Comparison of Input and Output Clamping

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

34. AD8475 : Funnel Amplifier + ADC Driver
+5V
SNR=97dB
4V 2.5V THD=-113dB
0.5V – 4.5V
+IN 0.4x VOUT(DIFF) ±4V
±10V 0V
-IN
20Ω
270pF 1.35nF
AD8475 AD7982
270pF
20Ω
+IN
VOCM 0.5V – 4.5V
-IN 0.4x VOUT(DIFF) ±4V REF
4V 2.5V
+5V
ADR435
10kΩ
0.1µF 10kΩ
 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

35. Balanced Audio Transmission System

36. Video Difference Amplifier with Variable
Common
AD830 allows different input and output common mode
voltage for matching ADC input range
VP
0.1µF
V1 1 AD830 8
INPUT GM
SIGNAL VOUT
V2 2 7
INPUT A=1
COMMON
3 6
GM C 0.1µF
4 5
VN
V3
VOUT = V1 – V2 + V3 OUTPUT
COMMON

37. 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

38. AD210 3-PORT ISOLATION AMPLIFIER
FB INPUT OUTPUT
T1
–IN _
DEMOD
_
MOD VO
+ FILTER +
+IN
ICOM OCOM
T2 POWER T3
+VISS INPUT OUTPUT +VOSS
POWER POWER
–VISS SUPPLY SUPPLY –VOSS
POWER
OSCILLATOR
PWR PWR COM

39. 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

40. MOTOR CONTROL CURRENT SENSING
HIGH VOLAGE
AC INPUT < 2500V RMS
+15V FB INPUT OUTPUT
T1
+ –IN _ _ OUTPUT
DEMOD
MOD VO
+IN + FILTER
AD620 +
0.01 RG OCOM
REF ICOM
_
–15V
+VISS T2 POWER T3
INPUT OUTPUT +VOSS
–VISS POWER POWER
SUPPLY SUPPLY –VOSS
RG = 499 POWER
M FOR G = 100 AD210 OSCILLATOR
PWR PWR COM
+15V

41. 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
www.analog.com/webcast

42. Next webcasts
 Challenges in Embedded Design for Motor Control systems
 April 13th at Noon (EDT)
 MEMs solutions for Instrumentation applications
 May 18th at Noon (EDT)
 Multi-Parameter Vital Signs Patient Monitors
 June 22nd at Noon (EDT)
www.analog.com/webcast

43. The World Leader in High Performance Signal Processing Solutions
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