Optimizing Data Converters for High Frequency Operation
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Transcript of Optimizing Data Converters for High Frequency Operation
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The World Leader in High-Performance Signal Processing Solutions
1. ADCs - Ping-Pong Architectures2. ADCs – Driving Them3. DACs – Sinc Compensation4. DACs – Glitches5. What They Didn’t Teach You in School
Optimizing Data Converters for High Frequency
Operation
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1.2
Ping Pong ADCsReferences
Analog Dialogue 37-8 (August 2003)
Analog Dialogue 39-5 (May 2005)
http://www.v-corp.com/
Do a Patent Search on Inventor: Velazquez; Classification: 341/118
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1.3
Nyquist Theorem Limits Frequency Bandwidth
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1.4
Ping-Pong ADCSArchitecture
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1.5
Ping-Pong ADCSRaw Spectral Response
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1.6
Ping-Pong ADCSMatching Requirements
Performance Requirement at 180
MHz
SFDR (dBc)
Gain Matching (%)
Aperture Matching
(fsec)
12 Bits 74 .04 0
12 Bits 74 0 350
12 Bits 74 .02 300
14 Bits 86 .01 0
14 Bits 86 0 88
14 Bits 86 .005 77
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1.7
Advanced Filter Bank (AFB)Reduces Spurs Due to ADC Mismatch
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1.8
Ping Pong ADCsTrimmed SFDR
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1.9
Ping Pong ADCsTemperature Effects
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1.10
Linear Error Compensation (LinComp)Corrects for Non-Linearities
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1.11
Driving ADCsReferences
Analog Dialogue 39-4 (April 2005)
Analog-Digital Conversion Seminar (2004)
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1.12
Transformer Coupling Gives Best High Frequency Performance
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1.13
ADC Drive
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1.14
Dual Transformers Improve Balance at High Frequencies
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1.15
Baluns Have a Wider Frequency Response
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1.16
Applying Voltage Gain Can Improve Noise Performance
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1.17
DACsSome Things You May Not Have Thought Of
Sinc Compensation Effects
Glitch Energy
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1.18
DACs Suffer From Sinc Response
-60
-50
-40
-30
-20
-10
0
0 0.5 1 1.5 2 2.5
Frequency (xFs)
dB
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1.19
Use Sinc Compensation to Reduce Passband Droop
Frequency (xFs)
dB
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
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1.20
Passband is Flat But There is 3.5 dB Insertion Loss
Frequency (xFs)
dB
-60
-50
-40
-30
-20
-10
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
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1.21
Sinc Compensation Doesn’t Work So Wellat Super Nyquist Bands
Frequency (xFs)
dB
-60
-50
-40
-30
-20
-10
0
0 0.5 1 1.5 2 2.5
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1.22
AD9779 Vs AD9777 Time Domain Plot
AD9777 AD9779
Both DACs synthesizing a 1MHz sine wave in 1x interpolation mode with a 160MSPS clock rate. Due to the unique output stage of the AD9779, its time domain waveform has much more glitch energy than the AD9777
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1.23
Glitches Are Worsebut Noise Floor is Better NSD Vs Fout FDATA = 160MSPS 2x Interpolation
-170
-165
-160
-155
-150
-145
-140
-135
-130
0 10 20 30 40 50 60 70
Fout - MHz
NS
D -
dB
m/H
z
AD9777_0dBFS AD9777_-6dBFS AD9779_0dBFS AD9779_-6dBFS
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1.24
Glitches Are Worsebut 3rd Order IMD Is better
1x Interpolation FDATA=160MSPS
50
55
60
65
70
75
80
85
90
95
100
0 10 20 30 40 50 60 70 80
Fout - MHz
IMD
- d
Bc
AD9777 AD9779
2x Interpolation FDATA=160MSPS
404550556065707580859095
100
0 20 40 60 80 100 120 140 160
Fout - MHz
IMD
- d
Bc
AD9777 AD9779
AD9779 Vs AD9779 IMD 4x FDATA=100MSPS
50
55
60
65
70
75
80
85
90
95
100
0 20 40 60 80 100 120 140 160 180 200
Fout - MHz
IMD
- d
Bc
AD9777 AD9779
AD9779 Vs AD9779 IMD 8x FDATA=50MSPS
404550556065707580859095
100
0 20 40 60 80 100 120 140 160 180 200
Fout - MHz
IMD
- d
Bc
AD9777 AD9779
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1.25
Things They Don’t Teach You In School
Watch ALL your inputs
Proper Decoupling
Differential Signaling
Clean Your Clock
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1.26
How many Inputs Does a Data Converter Really Have?
"QUIET“DIGITAL BUFFER
LATCH
NOISYDATA BUS
= DIGITALGROUND PLANE
DA
AGND DGND
IAID
BA
= ANALOGGROUND PLANE
Analog I/O
CSTRAY
A
A D
A
A
V
D
D
A
ANALOGCIRCUITS
A
Reference
VAVD
DIGITALCIRCUITS
CSTRAY
Clock
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1.27
Power Supply Decoupling Must Be Effective at Very High Frequencies
PROPER DECOUPLING NO DECOUPLING
VERTICAL SCALES: 10dB/div, HORIZONTAL SCALES: 10MHz/div
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1.28
Why Differential Signaling?
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1.29
How Clean Does Your Clock Need To Be
1 10 100 1000
0.1
1
10
100
1000
3 30 300
0.3
3
30
300
FULL-SCALE ANALOG INPUT FREQUENCY (MHz)
tj
(ps)
16
14
12
10
8
6
0.1
0.3
1
3
10
30
100
300
1000
18
4
tj
(ps)
ENOB = SNR –1.76dB
6.02
0.03 0.03
PLL WITH VCO
PLL WITH VCXO
DEDICATED LOW NOISE XTAL OSC
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1.30
In Conclusion
Hopefully you learned something
Getting good high-frequency performance is tough
But there are some things you can do to get the best performance you can
Thank you for your kind attention
Please talk to you friendly local ADI Sales Engineer when you’re ready to start your next design