The document presents a technique for improving the dynamic range of intermodulation distortion products in an arbitrary waveform generator using a phase switching algorithm. It discusses the challenges of current test instrumentation limitations and how a simple DSP method can extend performance while driving down testing costs. The findings suggest that this method can yield a significant reduction in IMD levels, which could translate to approximately a 1-bit improvement in ADC performance.

1. Confidential © ams AG
Peter Sarson CMgr MCMI SMIEEE
Full Service Foundry
10th April 2017
Shohei Shibuya,
Tomonori Yanagida,
Hauro Kobayashi
A Technique for
Dynamic Range Improvement of
Intermodulation Distortion Products
for
an Interpolating DAC-based
Arbitrary Waveform Generator
Using a Phase Switching Algorithm

2. 2
Outline
 Introduction
 Current Research
 Overview of Phase Switching Technique
 Details of the Simulation
 Measurement of the System
 Algorithm Modification for Interpolation DAC
 16 bit ADC Example
 Future Work & Conclusion

3. 3
Outline
 Introduction
 Current Research
 Overview of Phase Switching Technique
 Details of the Simulation
 Measurement of the System
 Algorithm Modification for Interpolation DAC
 16 bit ADC Example
 Future Work & Conclusion

4. 4
Outline
 Introduction
 Current Research
 Overview of Phase Switching Technique
 Details of the Simulation
 Measurement of the System
 Algorithm Modification for Interpolation DAC
 16 bit ADC Example
 Future Work & Conclusion


5. 5
Outline
 Introduction
 Current Research
 Overview of Phase Switching Technique
 Details of the Simulation
 Measurement of the System
 Algorithm Modification for Interpolation DAC
 16 bit ADC Example
 Future Work & Conclusion

6. 6
Outline
 Introduction
 Current Research
 Overview of Phase Switching Technique
 Details of the Simulation
 Measurement of the System
 Algorithm Modification for Interpolation DAC
 16 bit ADC Example
 Future Work & Conclusion

7. 7
Outline
 Introduction
 Current Research
 Overview of Phase Switching Technique
 Details of the Simulation
 Measurement of the System
 Algorithm Modification for Interpolation DAC
 16 bit ADC Example
 Future Work & Conclusion

8. 8
Outline
 Introduction
 Current Research
 Overview of Phase Switching Technique
 Details of the Simulation
 Measurement of the System
 Algorithm Modification for Interpolation DAC
 16 bit ADC Example
 Future Work & Conclusion

9. 9
Outline
 Introduction
 Current Research
 Overview of Phase Switching Technique
 Details of the Simulation
 Measurement of the System
 Algorithm Modification for Interpolation DAC
 16 bit ADC Example
 Future Works & Conclusion

10. 10
Introduction
 ATE test instrumentation becomes end of life
due to performance limitations
 Generates the need to buy
newer tester instrumentation
or new test platforms

11. 11
Introduction
 ATE test instrumentation becomes end of life
due to performance limitations
 Generates the need to buy
newer tester instrumentation
or new test platforms

12. 12
Introduction
 This in turn drives up test cost.
 When test cost is being constantly driven down!
 ADC testing is limited to the base performance
of the AWG that is stimulating it.
 I will show how to extend the base performance
of an Interpolating AWG
using a simple DSP technique.

13. 13
Introduction
 This in turn drives up test cost.
 When test cost is being constantly driven down!
 ADC testing is limited to the base performance
of the AWG that is stimulating it.
 I will show how to extend the base performance
of an Interpolating AWG
using a simple DSP technique.

14. 14
Introduction
 This in turn drives up test cost.
 When test cost is being constantly driven down!
 ADC testing is limited to the base performance
of the AWG that is stimulating it.
 I will show how to extend the base performance
of an Interpolating AWG
using a simple DSP technique.

15. 15
Introduction
 This in turn drives up test cost.
 When test cost is being constantly driven down!
 ADC testing is limited to the base performance
of the AWG that is stimulating it.
 I will show how to extend the base performance
of an Interpolating AWG using a simple DSP
technique.

16. Current Research
 Two-tone signal generation without IMD3
using AWG
 Simple DSP algorithm
 No need for AWG nonlinearity identification
 Gunma University group research
for standard DAC inside AWG
K. Kato et. al., “Two-tone Signal Generation for
Communication Application ADC Testing”,
IEEE Asian Test Symposium, Niigata, Japan (Nov. 2012)
16

17. 17
Overview of Phase Switching Technique
 Build a waveform that consists of two sinusoids
that switch between two phasors
that are equivalent to the harmonics
that needs to be suppressed
 𝑋1 𝑛 = 𝐴 sin 2𝜋𝑓1 𝑛𝑇𝑠 +
𝜋
2 𝐼𝑀𝐷
+ 𝐵 sin 2𝜋𝑓2 𝑛𝑇𝑠 −
𝜋
2 𝐼𝑀𝐷
n: odd
 𝑋2 𝑛 = 𝐴 sin 2𝜋𝑓1 𝑛𝑇𝑠 −
𝜋
2 𝐼𝑀𝐷
+ 𝐵 sin 2𝜋𝑓2 𝑛𝑇𝑠 +
𝜋
2 𝐼𝑀𝐷
n: even

18. Confidential © ams AG
Page 18
AWG
DAC
CLK
DSP
X XXX
Din
Din
AWG sampling frequency: fs(AWG) = 1/Ts
A
𝐗= Acos(2πfinnTs)
0 0.1 0.2 0.3 0.4 0.5
-300
-200
-100
0
Power[dB]
Normalized frequency f/fs
𝐟𝐢𝐧
𝐇𝐃𝟑
In case
Single-tone generation
DAC has 3rd-order distortion
Conventional Signal Generation with
AWG

19. Confidential © ams AG
Page 19
Signal Generation with AWG using
Phase Switching
AWG
DAC
CLK
DSP
X0 X1X0X1
Din
Din
AWG sampling frequency: fs(AWG) = 1/Ts(AWG)
𝐗 𝟎= 1.15Acos(2πfinnTs−π/6)
𝐗 𝟏= 1.15Acos(2πfinnTs+𝜋/6)
0 0.1 0.2 0.3 0.4 0.5
-300
-200
-100
0
𝐟𝐢𝐧
𝐟𝒔/2−𝟑𝐟in
𝐟𝒔/2−𝐟in
Power[dB]
Normalized frequency f/fs
Θ = π/3𝐓𝐬(𝐀𝐖𝐆)
X0
𝐗 𝟏
In case
Single-tone generation
DAC has 3rd-order distortion
HD3 disappears

20. 20
Simulation Details of IMD3 Suppression
Needs to be filtered off
for a real two-tone!
f1 f2f1 f2
3f1 3f2
3f1 3f2
2f1+f2 2f2+f1
2f1-f2 2f2-f1
Conventional Phase Switching

21. Measurement of the System
21
AWG
MEMORY
AWG FILTER
50MHz
DIGITIZER
FFT
Tester Result
Loopback

22. 22
Measurement of the System
REF
SUPP
2f1-f2 2f2-f1

23. 23
Measurement of the System
SUPP
REF

24. Measurement of the System
24

25. 25
Algorithm Modification for
Interpolation DAC
 What we see is something different
from the original equations, as below
 𝑋1 𝑛 = 𝐴 sin 2𝜋𝑓1 𝑛𝑇𝑠 +
𝜋
𝐼𝑀𝐷+1
+ 𝐵 sin 2𝜋𝑓2 𝑛𝑇𝑠 −
𝜋
𝐼𝑀𝐷+1
n: odd
 𝑋2 𝑛 = 𝐴 sin 2𝜋𝑓1 𝑛𝑇𝑠 −
𝜋
𝐼𝑀𝐷+1
+ 𝐵 sin 2𝜋𝑓2 𝑛𝑇𝑠 +
𝜋
𝐼𝑀𝐷+1
n: even

26. But ……………………
26
4th Harmonic of NCO and IMD5 suppression

27. What about Repeatability ?
27
Reference waveform looped 100 times
with starting phase varied – 2X

28. Effect of Phase and suppression –
IMD3 with IMD3 suppressed
28
Reference waveform compared with
IMD3 suppression and IMD3 measured

29. Effect of Phase and suppression –
IMD3 with IMD2 suppressed
29
Reference waveform compared with
IMD2 suppression and IMD3 measured

30. Effect of Phase and suppression –
IMD5 with IMD3 suppressed
30
Reference waveform compared with
IMD3 suppression and IMD5 measured

31. Effect of Phase and suppression –
IMD7 with IMD4 suppressed
31
Reference waveform compared with
IMD4 suppression and IMD7 measured

32. Effect of Phase and suppression –
IMD9 with IMD5 suppressed
32
Reference waveform compared with
IMD5 suppression and IMD9 measured

33. 33
Findings from Measurement Results

34. 34
Why ?

35. More Why ? My Guess ….
35
MIXER DAC
NCO
Din AoutDout
Assuming Square wave LO
Dout = a2
+ b3
+c4
Aout = a2
+ b3
+c4
NCO 2NCO 3NCO 4NCO 5NCO
IMD3
IMD5
IMD7
IMD9
Freq
Amplitude

36. 36
16 bit ADC Testing Example
AWG
MEMORY
AWG FILTER
50MHz
DUT
ADC
DIGITIZER
FFT
Tester Result
Testing System Configuration

37. 37
16 bit ADC Testing Example
Measurement Result
No suppression

38. 38
16 bit ADC Testing Example
Measurement Result
HD2 suppression

39. Future Work
 Remember, I am seeing this in an AWG
where an interpolating DAC is one of its parts.
 Need researchers to investigate harmonic
and Intermodulation distortion suppression
solely using Interpolating DAC’s
39

40. Conclusion
 Using two-tone phase switching techniques and
understanding the AWG architecture
it is possible to
• Decrease IMD across tester installed base
• With good repeatability
This can result in around a 6dB improvement
of the IMD3 and IMD5 products
~ 1-bit improvement Significant ! 40

41. Confidential © ams AG
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