A Technique for Dynamic Range Improvement of Intermodulation Distortion Products for an Interpolating DAC-based Arbitrary Waveform Generator Using a Phase Switching Algorithm

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
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
Outline
 Introduction

4
Outline
 Introduction


5
Outline
 Introduction

6
Outline
 Introduction

7
Outline
 Introduction

8
Outline
 Introduction

9
Outline
 Introduction
 Future Works & Conclusion

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
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
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
Introduction

14
Introduction

15
Introduction
of an Interpolating AWG using a simple DSP
technique.

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
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

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

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
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

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

22
REF
SUPP
2f1-f2 2f2-f1

23
SUPP
REF

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

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

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

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

29

30

31

32

33
Findings from Measurement Results

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

37
Measurement Result
No suppression

38
Measurement Result
HD2 suppression

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

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

Thank you
 Please visit our website www.ams.com

A Technique for Dynamic Range Improvement of Intermodulation Distortion Products for an Interpolating DAC-based Arbitrary Waveform Generator Using a Phase Switching Algorithm

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