Acquired analog signals can be manipulated and processed by either the analog or digital portions of a system, for example, through filtering, multiplexing, and gain control. The analog portions of a system can typically provide reasonably simple processing at fairly low cost, power, and overhead. Digital processing can provide far greater analysis power and can alter the nature of the analysis without changing hardware. Sampling theory, however, must be taken into account. This session covers the signal chain basics from signal to sensor to amplifier to converter to digital processor and back out again.

1. Advanced Techniques of Higher Performance Signal Processing
Partitioning Data Acquisition
Systems

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2

3. Today’s Agenda
The dilemmas of system architecture and partitioning
Analog vs. digital signal processing
The perils of sampling
Digital vs. digital
Where to put all the processing functions
 Gain
 Sampling
 Filtering
 Multiplexing
 Special analog processing
 Isolation
3

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

5. … in the Beginning …
There was a sensor, mechanical driver, stylus, recording medium,
playback stylus, and mechanical amplifier – it worked
5

6. … and Then We Added Electronics …
6

7. Current Day Integrated Functions
Audio codecs
SoundMAX® computer audio
codecs
I/O ports
Mixed-signal front ends:
modems, communications, CCD
imaging, flat panel displays
Transmit and receive signal
processors
Direct conversion radio
Energy metering
Video encoders/decoders,
codecs
Touchscreen digitizers
Analog microcontrollers (high
performance ADCs, DACs, and
ARM µP core and flash memory)
Blackfin® DSPs with on-board
ADCs and DACs
Motion sensors with embedded
ADCs
7

8. The Dilemmas of Partitioning
Why Digitize at All?
Analog vs. Digital Processing
 Filtering
 Linearization
 Detection
Multiplexing
 Multiple amplifiers, filters, converters
 Simultaneous sampling
Signal Control
 Gain ranging vs. high resolution
 Compression
 Filtering
8

9. Analog and Digital Domains
Why Convert to Digital?
Analog signals are continuous and provide the entire signal
Digital signals capture only a portion of the signal
Why digitize?
 Improved signal analysis potential
 More robust storage
 More accurate transmission
 Higher order filters implemented with less cost
Development objective of sampled data systems is to minimize
effect of the sampling process
9

10. Analog vs. Digital Design
Analog Design Advantages
 Simpler and quicker to implement
 Lower power
 Analog systems don’t crash and need reboot
Disadvantages
 Difficult to change once in production – or at a customer
 Limited scale
Digital Design Advantages
 Changeable without hardware modification
 More filtering capability and scale
 Not sensitive to temperature
Disadvantages
 Initial software design takes longer
 More complex hardware
 Requires ADC that determines the SNR
10

11. Digital vs. Digital Design
FPGA vs. DSP
FPGA Pros
 Deliver higher performance through very high parallelism
 Flexible I/O to support high-speed analog interfaces
 Low fixed costs
 Quick design turns for hardware changes
FPGA Cons
 Higher power in redundant logic
 Higher cost at volume
DSP Pros
 Programming is simpler – many libraries and third-party support companies
 Higher speed for straight processing
DSP Cons
 Fixed hardware structure
 Limited scale for parallel processing
11

12. The Costs of Digitizing Signals
You need to learn sampling theory
The input signal will be compromised – the goal is to determine
what’s acceptable
The input signal needs to be filtered
Signal reconstruction will require another data converter
12

13. Many Types of Sampled Data Systems
Analog-to-Digital Converters
Digital-to-Analog Converters
Sample-and-Hold Amplifiers
Peak Detectors
Comparators
Switched Cap Filters
Samples a Continuous Signal
Domain Conversion
 Analog to digital
 Digital to analog
 Continuous time to discrete time
 Continuous frequency to discrete
frequency
Sampling Rate
 Continuous, discontinuous
13

14. Sampled Data System: Sampling
and Quantization
LPF
OR
BPF
N-BIT
ADC
DSP
N-BIT
DAC
LPF
OR
BPF
fa
fs fs
t
AMPLITUDE
QUANTIZATION DISCRETE
TIME SAMPLING
fa
1
fs
ts=
14

15. RESOLUTION
N
2-bit
4-bit
6-bit
8-bit
10-bit
12-bit
14-bit
16-bit
18-bit
20-bit
22-bit
24-bit
2N
4
16
64
256
1,024
4,096
16,384
65,536
262,144
1,048,576
4,194,304
16,777,216
VOLTAGE
(10V FS)
2.5 V
625 mV
156 mV
39.1 mV
9.77 mV (10 mV)
2.44 mV
610 V
153 V
38 V
9.54 V (10 V)
2.38 V
596 nV*
ppm FS
250,000
62,500
15,625
3,906
977
244
61
15
4
1
0.24
0.06
% FS
25
6.25
1.56
0.39
0.098
0.024
0.0061
0.0015
0.0004
0.0001
0.000024
0.000006
dB FS
– 12
– 24
– 36
– 48
– 60
– 72
– 84
– 96
– 108
– 120
– 132
– 144
*600nV is the Johnson Noise in a 10kHz BW of a 2.2k Resistor @ 25°C
Remember: 10-bits and 10V FS yields an LSB of 10mV, 1000ppm, or 0.1%.
All other values may be calculated by powers of 2.
Quantization: The Size of a Least Significant Bit
(LSB)
15

16. Practical Resolution Needs for Data Converters
Instrumentation Measurements
 Sensor resolution/accuracy of 0.5% = 1/200
 8 bits equivalent to 1/256 -- digitizing will lose information
 10x sensor resolution = 1/2000 -- 12 bits is 1/4096
 Allows discrimination of small changes
 Can also be driven by display requirements
Dynamic Signal Measurements
 Audio systems need better than 0.1% distortion at 5% of full scale
 Equivalent to 1/20,000 -- 16 bits is 1/65,536
16

17. Ideal ADC Sampling
3 Different Frequencies, Sampled the Same
17

18. Ideal ADC Sampling
Once Sampled, Information Is Lost
18

19. Baseband Antialiasing Filter Requirements
A
DR
fs
fa fs - fa
fs
2
STOPBAND ATTENUATION = DR
TRANSITION BAND: fa to fs - fa
CORNER FREQUENCY: fa
Antialias Filter Prevents
Aliasing
Contributes to Dynamic Range
Antialias Filter Objectives
 Brick Wall (Steep/Deep Rolloff)
 Linear Passband
 Linear Phase
19

20. A Key Partitioning Question—Where to Filter?
Analog Filtering
 Hardware oriented—generally fixed design
Digital Filtering
 Software oriented—offers more flexibility
20

21. Purposes of Filtering
Noise Reduction
 Typically low-pass
Discrimination and Selection
 RF detection – channel separation
 Extracting small signals from noise
Signal Enhancement
 Music
Filter Complexity Derives from the Requirement
21

22. Types of Filters
Types of Analog filters
 Active
 More common at lower frequencies
 Passive
 More common at higher frequencies
Types of Digital filters
 IIR (infinite impulse response)
 Based on analog filters
 More computationally efficient
 FIR (finite impulse response)
 Can be linear phase
 More computationally intensive
 Can provide more power and flexibility
Digital filtering requires digitizing—which requires an analog anti-
aliasing filter before the analog-to-digital converter
22

23. Comparing Analog and Digital Filters
Analog
 No computational limitations
to limit high frequency
operation
 Subject to component drift
and accuracy
 Simpler circuit
 Unlimited dynamic range
 Basically no latency
Digital
 Computations must be
completed in sampling time—
limits real-time operation
 Not subject to component
drift and accuracy
 More complex circuit
 Requires antialiasing filter,
ADC, DSP, DAC, and
reconstruction filter
 Dynamic range limited by
converter resolution
 Much higher latency (delay)
 Some filter functions can only
be done digitally
23

24. Analog vs. Digital Filter Frequency
Response Comparison

25. Digital Filtering

26. Throughput Considerations for Digital Filters
A digital biquad is a second-order recursive linear filter containing
two poles and two zeros
Determine how many biquad sections (N) are required
to realize the desired frequency response
Multiply this by the number of instruction cycles per
biquad for the DSP and add overhead cycles
The result (plus overhead) is the minimum allowable
sampling period (1 / fs) for real-time operation
26

27. Comparison Between IIR and FIR Filters

28. Sigma-delta ADC -- the multi-purpose part
Sigma-delta ADCs span the analog and digital world
Provide customized filtering and high-resolution data
conversion
The core of digital audio processing
28

29. 29
Sigma-Delta ADC - First-Order Modulator
  +
_
+VREF
–VREF
DIGITAL
FILTER
AND
DECIMATOR
+
_
CLOCK
Kfs
VIN
N-BITS
fs
fs
A
B
1-BIT DATA
STREAM1-BIT
DAC
LATCHED
COMPARATOR
(1-BIT ADC)
1-BIT,
Kfs
SIGMA-DELTA MODULATOR
INTEGRATOR

30. Sampled Data System:
Sampling and Quantization

31. 31
Simplified Frequency Domain Linearized Model
of a Sigma-Delta Modulator

ANALOG FILTER
H(f) = 1
f

X Y
+
_
X – Y
1
f
( X – Y )
Q =
QUANTIZATION
NOISE
Y =
1
f
( X – Y ) + Q
REARRANGING, SOLVING FOR Y:
Y =
X
f + 1
+
Q f
f + 1
SIGNAL TERM NOISE TERM
Y

32. 32
Oversampling, Digital Filtering,
Noise Shaping, and Decimation
fs
2
fs
Kfs
2
Kfs
KfsKfs
2
fs
2
fs
2
DIGITAL FILTER
REMOVED NOISE
REMOVED NOISE
QUANTIZATION
NOISE = q / 12
q = 1 LSBADC
ADC
DIGITAL
FILTER
SD
MOD
DIGITAL
FILTER
fs
Kfs
Kfs
DEC
fs
Nyquist
Operation
Oversampling
+ Digital Filter
+ Decimation
Oversampling
+ Noise Shaping
+ Digital Filter
+ Decimation
A
B
C
DEC
fs

33. Data Acquisition Subsystem Configuration
Multiplexing
 Multiple preamps
 Multiple anti-alias filters
 Multiple ADCs
 Gain
 Adjustable gain per channel
 PGA vs. high resolution ADC
Simultaneous Sampling
 Multiple signals correlated in time
Noise Reduction/Antialiasing Filter Placement
Special Analog Processing
Isolation
33

34. Data Acquisition Subsystem Configuration
Multiplexing
Multiplexing is done to reduce system cost by using fewer ADCs
 ADC is fast enough to handle all channels in sequence
 ADC errors are the same for all channels
Multiplexing issues
 Settling time after switching channels
 Multiplexer impedance may compromise signal
 Final buffer amplifier may be needed
 Multiplexer switching transients
Correlated sampling may require a faster solution
 How close in time sampling needs to be done
 Nyquist theory determines how often each signal needs to be sampled
 Total signal throughput rate
 Simultaneous sampling at lower rates
 Simultaneous conversion at higher rates
34

35. Simple ADC Multiplexing—AD7298
8 inputs plus temp sensor and single track/hold
35

36. Simultaneous Sampling—AD7606
8 Track/Hold Inputs Sampled Together
V1
V1GND
RFB1MΩ
1MΩ RFB
CLAMP
CLAMP
SECOND-
ORDER LPF
T/H
V2
V2GND
RFB1MΩ
1MΩ RFB
CLAMP
CLAMP
SECOND-
ORDER LPF
T/H
V3
V3GND
RFB1MΩ
1MΩ RFB
CLAMP
CLAMP
SECOND-
ORDER LPF
T/H
V4
V4GND
RFB1MΩ
1MΩ RFB
CLAMP
CLAMP
SECOND-
ORDER LPF
T/H
V5
V5GND
RFB1MΩ
1MΩ RFB
CLAMP
CLAMP
SECOND-
ORDER LPF
T/H
V6
V6GND
RFB1MΩ
1MΩ RFB
CLAMP
CLAMP
SECOND-
ORDER LPF
T/H
V7
V7GND
RFB1MΩ
1MΩ RFB
CLAMP
CLAMP
SECOND-
ORDER LPF
T/H
V8
V8GND
RFB1MΩ
1MΩ RFB
CLAMP
CLAMP
SECOND-
ORDER LPF
T/H
8:1
MUX
AGND
BUSY
FRSTDATA
CONVST A CONVST B RESET RANGE
CONTROL
INPUTS
CLK OSC
REFIN/REFOUT
REF SELECT
AGND
OS 2
OS 1
OS 0
DOUTA
DOUTB
RD/SCLK
CS
PAR/SER/BYTE SEL
VDRIVE
16-BIT
SAR
DIGITAL
FILTER
PARALLEL/
SERIAL
INTERFACE
2.5V
REF
REFCAPB REFCAPA
SERIAL
PARALLEL
REGCAP
2.5V
LDO
REGCAP
2.5V
LDO
AVCCAVCC
DB[15:0]
AD7606
08479-001
36

37. Full High Speed Dual Sampling—AD9643
2 Complete Sampling ADCs at 170 MHz
14
14
REFERENCE
SERIAL PORT
SCLK SDIO CSB CLK+ CLK– SYNC
1 TO 8
CLOCK
DIVIDER
AD9643
VIN+A D0±
D13±
DCO±
OR±
PDWN
OEB
VIN–A
VIN+B
VCM
VIN–B
NOTES
1. THE D0± TO D13± PINS REPRESENT BOTH THE CHANNEL A
AND CHANNEL B LVDS OUTPUT DATA.
AVDD AGND DRVDD
09636-001
.
.
.
.
.
PARALLEL
DDR LVDS
AND
DRIVERS
PIPELINE
14-BIT
ADC
PIPELINE
14-BIT
ADC
37

38. Positioning the Noise Reduction Filter to
Reduce the Effects of the Op Amp Noise
 ADCs often have very high input bandwidths, usually greater than fs/2
 Low distortion drive amplifiers typically have high bandwidths
 Placing a simple LPF or BPF placed between the amp and the ADC is
an excellent noise reduction technique
 Filter output impedance must be able to drive ADC
 The output capacitor of the filter absorbs some of the ADC input
transient currents.
2.38
fFILTER
AMP
AMP
LPF
OR
BPF
LPF
OR
BPF
ADC
ADC
fFILTER
fs
fs
fCL
fCL
fADC
fADC
(A)
(B)
Amp noise integrated
over amp BW or ADC BW,
whichever is less
Amp noise integrated
over filter noise
bandwidth only

39. Where to Put the Gain?
Partitioning question about using PGA vs. high resolution ADC
PGA with wide-range gain steps can extend effective resolution of
ADC
 Provides fine resolution
 Not an exact solution unless gain ranges are perfectly matched
 Nonlinearity induced between ranges
Not as popular with advent of higher resolution ADCs
Still useful in certain applications
39

40. ADC Multiplexing with Programmable Gain—
AD7194
16 inputs plus temp sensor and programmable gain amplifier
Accommodates sensors with widely varying signal levels
40
DVDD DGND REFIN1(+) REFIN1(–)
AIN1/P3
AIN2/P2
AIN3/P1/REFIN2(+)
AIN4/P0/REFIN2(–)
AINCOM
AD7194
SERIAL
INTERFACE
AND
CONTROL
LOGIC
REFERENCE
DETECT
TEMP
SENSOR
DOUT/RDY
DIN
SCLK
CS
MCLK1 MCLK2
CLOCK
CIRCUITRY
AVDD AGND
AIN5
AIN16
Σ-Δ
ADC
PGA
MUX
08566-001
AVDD
AGND

41. Special Analog Processing and Special Cases
Certain sensors require specialized analog processing to extract
precise measurements
 Thermocouples—cold-junction compensation
 Wide-dynamic-range photodiodes—signal compression
 Linearization
Some sensors require precision tuning per unit—others can be
tuned together
Calibration and replacement issues
Digital options—store adjustment coefficients in software
Isolation
 Analog or digital
 Power isolation
41

42. Thermocouples
Thermocouples require cold-junction compensation
 Traditionally done with specialized amplifiers with internal temperature sensors
 Newer techniques use high-accuracy temperature sensors and A-D converters
to allow compensation at the processor
Thermocouple non-linearity is non-linear
 Difficult to construct analog compensation
 Digital systems use look-up tables
Detailed analysis in the Low-Level Signal Acquisition session
42

43. High Accuracy Multichannel Thermocouple
Measurement Solution (CN0172)
43

44. 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%
Digital compression alternative
 Programmable gain amplifier combined with high-resolution ADC
 Can achieve range out to 120dB
 Limited at very high frequencies

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

46. 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
ERROR(dB)
INPUT LEVEL (dBm)
AD8307 covers 80dB with 0.5dB accuracy

47. AD8307 six-decade RF power
measurement
TO
ANTENNA
VP
604Ω
100kΩ
1/2W
NC
2kΩ
VR1
2kΩ
INT ±3dB
51pF
51pF
0.1µF
NC
OUTPUT
LEAD-
THROUGH
CAPACITORS,
1nF
1nF
NC = NO CONNECT
+5V
VOUT
AD8307
INP VPS ENB INT
INM COM OFS OUT
8 7 6 5
2 3 41
50Ω INPUT
FROM P.A.
1µW TO
1kW
22Ω

48. Oversampled SAR ADC with PGA
Achieving Greater Than 125 dB
Dynamic Range (CN0260)
Dynamic gain ranging
Faster than high-resolution sigma delta
Sampling rate up to 2.5MSPS
48

49. Oversampled SAR ADC with PGA Achieving
Greater Than 125 dB Dynamic Range
(CN0260)
49

50. Where to Put the Isolation?
Isolation is used to galvanically separate systems
 Safety in patient monitoring
 High-voltage systems
 Remove high common-mode noise
Most commonly done at the digital level
 ADC converter signal to digital
 Transmitted across digital isolators
Providing power to isolated circuits needed
High-voltage amplifiers suitable in some motor control or power
control systems
More detail in the Data and Power Isolation session
50

51. 500 V Common-Mode Voltage Current Monitor
(CN0218)
51
AD8212

52. 52
Bidirectional Isolated High-Side Current Sense
with 270 V Common-Mode Rejection (CN0240)

53. Novel Analog-to-Analog Isolator Using an
Isolated Sigma-Delta Modulator, Isolated
DC-to-DC Converter, and Active Filter (CN0185)
53

54. Reverse Partitioning
Smarter peripheral devices sensing local conditions
Make local decisions to off-load main processor
Reduce programming load
Automatic gain control
Power control
54

55. Reverse Partitioning—AD5755
Quad 16-bit DAC for 4–20 mA industrial signaling
Dynamic power control for thermal management
On-chip diagnostics
55

56. Flexible 4-Channel Analog Front End for Wide
Dynamic Range Signal Conditioning (CN0251)
This circuit has it all
Multiplexing front-end
Multiplexer buffer
Instrumentation amplifier for CMRR
Anti-alias filter
Funnel amplifier to fit ADC range
Internal programmable gain amplifier
 Gain ranges trimmed and matched
Sigma-delta ADC provides noise shaping
56

57. Flexible 4-Channel Analog Front End for Wide
Dynamic Range Signal Conditioning (CN0251)
57

58. Tweet it out! @ADI_News #ADIDC13
What We Covered
The dilemmas of system architecture and partitioning
Analog vs. digital signal processing
The perils of sampling
Digital vs. digital
Where to put all the processing functions
 Gain
 Sampling
 Filtering
 Multiplexing
 Special analog processing
 Isolation
58

59. Tweet it out! @ADI_News #ADIDC13
Visit the Flexible 4-Channel Analog Front End
for Wide Dynamic Range Signal Conditioning
(CN0251) in the Exhibition Room
This flexible signal conditioning
circuit is for processing signals
of wide dynamic range, varying
from several mV p-p to 20 V p-p.
The circuit provides the
necessary conditioning and
level shifting and achieves the
dynamic range using the internal
programmable gain amplifier
(PGA) of the high resolution
analog-to-digital converter
(ADC).
59
Image of demo/board
This demo board is available for purchase:
www.analog.com/DC13-hardware

60. Tweet it out! @ADI_News #ADIDC13
FMComms1 Demo in the Exhibition Hall
New partitioning concepts for radio
Ubuntu Linux on ZC702
FMComms1 on FMC
HDMI Display and USB
Keyboard/Mouse
Full Transmit and Receive
60
Image of demo/board
This demo board is available for purchase:
www.analog.com/DC13-hardware