Using Distortion Shaping Technique to Equalize ADC THD Performance Between ATEs
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Transcript of Using Distortion Shaping Technique to Equalize ADC THD Performance Between ATEs
Confidential © ams AG
Using Distortion Shaping Technique to Equalize ADC THD Performance Between ATEs
IMSTW 16
Peter Sarson CMgr MCMI SMIEEEFull Service Foundry
4th July 2016
Prof Hauro Kobayashi Gunma University
Confidential © ams AGPage 2
Introduction
• During development of any test program test engineers sometimes face the issue that the tester isn’t as good as the chip
• This causes issues when device specs need testing and the limit cannot be reached
• Kobayashi will show some mathematics: harmonic distortion contents can be shifted up close to Nyquist frequency.
• Peter will show how the harmonic performance of an ATE’s AWG can be improved using this approach
• Peter will show how this approach improved the result and reproducibility of a 12-bit ADC testing
• Peter will show how this approach improved the result of a 16-bit ADC testing that was limited by the tester performance
Confidential © ams AGPage 3
Research Objective
Low distortion signal generation with AWG for low cost and high quality testing of ADC
Investigation of phase switching signal generation method with experiment at ATE environment
• No need for AWG nonlinearity identification• Only DSP program change
Confidential © ams AGPage 4
ADC test signal Test result
ADC Testing with Sine Signal
Freq.
ADC HD3
Freq.
“No Go”
“Go”
Freq.
Reference level
Allowable
fundamental
Freq.
Test result
fundamental
AWG ADC
𝑍=𝑏1𝑌 +𝑏3𝑌 3
fin 3fin
fin 3fin
fin 3fin
fin
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ADC test signal Test result
Problem of Conventional Method
AWG HD3+ADC HD3.
Freq.
fundamental
Freq.
Test result
AWG ADC
𝑍=𝑏1𝑌 +𝑏3𝑌 3fundamental
fin 3fin
fin
Test signal generationY=a1Din + a3Din
3
3fin
AWG HD3
HD3
ADC HD3 cannot be measured accurately
Low quality test
Confidential © ams AGPage 6
ADC test signal Test result
Research Goal
Only ADC HD3
Freq.
fundamental
Freq.
Test result
AWG ADC
𝑍=𝑏1𝑌 +𝑏3𝑌 3fundamental
fin 3fin
fin
Test signal generationY=a1Din + a3Din
3
3fin
AWG HD3 reduction
HD3
High quality testOnly program change
Confidential © ams AGPage 7
Conventional Signal Generation with AWG
AWG
DACCLK
DSP
X XXX
Din
Din
AWG sampling frequency: fs(AWG) = 1/Ts
A
𝐗= Acos(2πf_in nT_s)
0 0.1 0.2 0.3 0.4 0.5-300
-200
-100
0
Pow
er [d
B]
Normalized frequency f/fs
𝐟 𝐢𝐧
𝐇𝐃𝟑
Confidential © ams AGPage 8
Proposed Signal Generation with AWG
AWG
DACCLK
DSP
X0 X1X0X1
Din
Din
AWG sampling frequency: fs(AWG) = 1/Ts(AWG)
𝐗𝟎= 1.15Acos(2πf_in nT_s−π/6)𝐗𝟏=1.15Acos(2πfin nTs+ /6)𝜋0 0.1 0.2 0.3 0.4 0.5
-300
-200
-100
0𝐟 𝐢𝐧
𝐟 𝒔/2−𝟑𝐟 ¿
𝐟 𝒔/2−𝐟 ¿
Pow
er [d
B]
Normalized frequency f/fs
Θ = π/3𝐓𝐬 (𝐀𝐖𝐆)
X 0
𝐗𝟏
Confidential © ams AGPage 9
Principle of 3rd Harmonics CancellationTwo waves with phase difference π are cancelled
Con
vent
iona
lPh
ase
Switc
hing
Θ = π/3 3Θ = π
3rd o
rder
non
-line
ar s
yste
mP
hase
rota
tion
by x
3
fundamental: fin 3rd harmonics: 3 fin
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X0=Asin(2πfint+π/4) X1=Asin(2πfint-π/4)
HD2 Cancellation2-way interleave cancels HD2
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X0=Asin(2πfint-π/4-π/6)X2=Asin(2πfint+π/4-π/6)
X1=Asin(2πfint-π/4+π/6)X3=Asin(2πfint+π/4+π/6)
HD2, HD3 Cancellation4-way interleave cancels HD2 & HD3
Confidential © ams AGPage 12
Be Careful
If you use this technique without filtering the generated high-frequency spurious
Harmonic contents of the ADC under test will be under-estimated.
These spurious components need filtering outto get back normal sinewave without harmonics.
More detailed later.
Confidential © ams AGPage 13
How to Do in Software2-signal interleaved
Element 1
Element 2
Element 3
Element 4
Element 5
Element 6
Element 7
Element 8
Array 1 1 2 3 4 5 6 7 8
Array 2 9 10 11 12 13 14 15 16
Supressed 1 10 3 12 5 14 7 16
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How to Do in Software4-signal interleaved
Element 1
Element 2
Element 3
Element 4
Element 5
Element 6
Element 7
Element 8
Array 1 1 2 3 4 5 6 7 8
Array 2 9 10 11 12 13 14 15 16
Array 3 17 18 19 20 21 22 23 24
Array 4 25 26 27 28 29 30 31 32
Supressed 1 10 19 28 5 14 23 32
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Test Setup for Measuring Tester Performance
AWGMEMORY
AWG FILTER50MHz
DIGITIZERFFTTester Result
Loopback
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Tester 1 3rd Harmonic ReductionMeasured spectrum level improvement of reference vs suppressed 3rd harmonic for AWG.
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Tester 1: 3rd and 5th Harmonic ReductionMeasured spectrum level improvement of reference vs suppressed 3rd & 5th harmonics for AWG.
Confidential © ams AGPage 18
Harmonic ReductionMeasured Harmonic Performance Improvement for AWG Using the Proposed Method
Harmonic Improvement
2nd6 dB
3rd16 dB
4th18 dB
5th23 dB
Confidential © ams AGPage 19
ADC Performance Test Setup
AWGMEMORY
AWG FILTER50MHz
DUT ADC
DIGITIZERFFTTester Result
Confidential © ams AGPage 20
12-bit ADC Results Tester 1
signal Thd std units
ref 89,7 2,5 dB
2nd_red 89,8 2,1 dB
3rd_red 89,3 2 dB
4th_red 89,5 2,1 dB
5th_red 89,2 2,6 dB
2nd,4th_red 91 2,4 dB
3rd,5th_red 89,7 2,5 dB
Confidential © ams AGPage 21
12-bit ADC Results Tester 1
signal Thd std units
ref 89,7 2,5 dB
2nd_red 89,8 2,1 dB
3rd_red 89,3 2 dB
4th_red 89,5 2,1 dB
5th_red 89,2 2,6 dB
2nd,4th_red 91 2,4 dB
3rd,5th_red 89,7 2,5 dB
Confidential © ams AGPage 22
12-bit ADC Results Tester 1
signal Thd std units
ref 89,7 2,5 dB
2nd_red 89,8 2,1 dB
3rd_red 89,3 2 dB
4th_red 89,5 2,1 dB
5th_red 89,2 2,6 dB
2nd,4th_red 91 2,4 dB
3rd,5th_red 89,7 2,5 dB
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12-bit ADC Harmonic Suppressed Result2nd and 4th suppressed delta and overall THD Improvement
THd ref THd supp
Tester 2 88,7dB 91dB
Tester 1 89,6dB 91dB
Without suppression:• Different measured values of THD performance
With Suppression:• Exactly the same result between Testers 1 & 2
Confidential © ams AGPage 24
Site to Site Comparison No difference between sites with the proposed method!
12-bit ADC testing case
Tester 1 Site 1 Site 2 delta
Red 91dB 91,1dB 0,1dBref 89,6dB 89,6dB 0dB
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3rd, 5th and 7th Suppressed
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How 8-signal interleaved looks like2^3 = 8
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3-Harmonics (3rd , 5th & 7th Harmonics) Suppression
Using 3-harmonics suppression algorithm, effect of the sidebands would be SB= fs/8 – 7*fin
Maximum sampling freq. (fs) of AWGHSB : 250MHz Signal freq. (fin): 1MHz
Filter with 24MHz cutoff is needed
Not available on AWGHSB
Need a load-board filter.
Confidential © ams AGPage 28
OVERSAMPLE = 1FS: 259.2000 kHz
THD = -89.83dB
Another Example – Tester 1 (Conventional)Obelic 16-bit ADC – no suppression, direct conversion
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OVERSAMPLE = 1FS: 259.2000 kHz
THD = -89.83dB
Another Example – MX01 (Conventional)16-bit ADC – no suppression, direct conversion
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OVERSAMPLE = 600FS: 155.5200 MHz
THD = -115.09dB
MUCH BETTER
Obelic 16-bit ADC – 2nd Harmonic Suppressed (Proposed)Oversample 600 times – Tester 1
Confidential © ams AGPage 31
OVERSAMPLE = 600FS: 155.5200 MHz
THD = -113.87dB
Same as Tester 1
16bit ADC – 2nd Harmonic Suppressed (Proposed)Oversample 600 times – Tester 2
Confidential © ams AGPage 32
Performance summary
Using a 12-bit ADC, testing performance can be improved but you are limited to the noise performance of the ADC itself
• If spec limits are an issue, the technique can help squeeze out some margin
Using a 16-bit ADC, performance can be significantly improved (say, by 25 dB) as the noise floor is much lower due to the number of bits.
Effectiveness of the distortion-shaping technique was verified with ATE environment.
Confidential © ams AG
Thank you
Please visit our website www.ams.com
Confidential © ams AGPage 34
Appendix
Proposed signal generation method• Distortion components close to signal band are reduced• Distortion components far from signal band may appear.
Similar to but different from noise-shaping
Distortion-shaping
Normalized frequency f/fs