21/Sep/2011

GunmaUniversity KobayashiLab

International Test Conference 2011 Poster No.19

Low-Distortion Single-Tone and Two-Tone Sinewave Generation

Using Σ∆ DAC

T. Yamada, O. Kobayashi, K. Kato, K. Wakabayashi,

H. Kobayashi, T. Matsuura, Y. Yano, T. Gake,

K. Niitsu, N. Takai, T. J. Yamaguchi

Gunma University

Semiconductor Technology Academic Research Center

1

Outline

• Research Purpose

• ADC Testing Signal Generation with ΣΔDAC

• Conventional Test Method

• Proposed Test Method

• Experimental Results

• Conclusion2

Outline

• Research Purpose

• ADC Testing Signal Generation with ΣΔDAC

• Conventional Test Method

• Proposed Test Method

• Experimental Results

• Conclusion3

Research Purpose

4

Proper-quality low-cost testing of ADCs in SoC

Signal

generator

Semiconductor

device

Signal

generator

Semiconductor

device

Conventional method Proposed method

Low-distortion sinusoidal signal generation

with DSP and DAC cores in SoC

Outline

• Research Purpose

• ADC Testing Signal Generation with ΣΔDAC

• Conventional Test Method

• Proposed Test Method

• Experimental Results

• Conclusion5

ΣΔDAC Configuration

6

ΣΔDAC ⇒ can be implanted with DSP and DAC cores

inside SoC in test mode

ΣΔDAC

∫－

Multi-bit

DAC

Digital

inputAnalog

output

Digital circuit Analog circuit

Internal DAC

Q

Outline

• Research Purpose

• ADC Testing Signal Generation with ΣΔDAC

• Conventional Test Method

• Proposed Test Method

• Experimental Results

• Conclusion7

Ideally Linear ΣΔDAC

8

DSPΣΔ

DAC

Signal

Generator

DAC

The same frequency of input and output signals

Input frequency Output frequency

Y = aX

Y = aX

ffin

ffin

sin(2πfint)

Actual ΣΔ DAC Single-tone Generation

9

ffin

DAC

Output has 3rd order harmonic distortion(HD3)

sin(2πfint)

ffin 3fin

Input frequency Output frequency

ΣΔ

DAC

Y = aX + bX3

Y = aX + bX3

DSP

Signal

Generator

Y = a(X1+X2)

+ b(X1+X2)3

Actual ΣΔ DAC Two-tone Generation

10

Output has 3rd order Inter-modulation distortion(IMD3)

Y = aX + bX3

f

f 1 f 2

2f 1

-f2

2f 2

-f1

2f 1

+f 2

2f 2

+f 1

3f 2

3f 1

ff1 f2

DAC

Input frequency Output frequency

sin(2πf1t)

+sin(2πf2t)

IMD3 components are difficult to remove by analog filter

ΣΔ

DACDSP

Signal

Generator

Outline

• Research Purpose

• ADC Testing Signal Generation with ΣΔDAC

• Conventional Test Method

• Proposed Test Method

• Experimental Results

• Conclusion11

Proposed Method

12

∫－

Multi-bit

DAC

Digital circuit Analog circuit

DSPInput Din

Y = aX + bX3

Output Y

ΣΔDAC

ck

Din=X1 Din=X2

Interleave X1 , X2 generate Din

Distortion components cancellation of output Y

Q

Din=Asin(2πfint+π/6)

Din=Asin(2πfint-π/6)

ck

Principle of Proposed Method

13

∫

－

Multi-bit

DAC

Digital circuit Analog circuit

Y = aX + bX3

ΣΔDAC

Q

Re

Im

Signal component

Phase deference

π/3

Re

Im

Phase deference

3・π/3 = π

Distortion component

Y = aX + bX3

Multi-bit

DAC

Single-tone Signal Generation

14

3finf

fin

Din=Asin(2πfint+π/6) Din=Asin(2πfint-π/6)

ck

fin fs/2-fin

f

ck

ΣΔ

DACDSP

Output Y

Y = aX + bX3

Input Din

HD3 cancellation

Two-tone Signal Generation

15

f1f s

/2-f

2

ff2

f s/2

-f1

Din=Asin(2πf1t+π/6)

+Bsin(2πf2t-π/6)

Din=Asin(2πf1t-π/6)

+Bsin(2πf2t+π/6)

ck

ck

ΣΔ

DACDSP

Output Y

Y = aX + bX3

Input Din

f

f 1 f 2

2f 1

-f2

2f 2

-f1

2f 1

+f 2

2f 2

+f 1

3f 2

3f 1

IMD3 cancellation

For communication application ADC

Outline

• Research Purpose

• ADC Testing Signal Generation with ΣΔADC

• Conventional Test Method

• Proposed Test Method

• Experimental Results

• Conclusion16

Experiment Condition

17

RBW : Resolution band

width (Hz)1k

VBW : Video band

width (Hz)100k

Input frequency (Hz) 200k

Input amplitude (Vpp) 1

Sampling frequency (Hz) 8M

Max. Sampling

frequency (Hz)40M

Resolution (bit) 12

Linearity △

Frequency range (Hz) 9k～1.5G

Max amplitude (Vpp) 19.8

AWG Agilent 33120A Spectrum Analyzer : hp ESA-L1500A

Experiment Results : Single-tone Signal

18

0

-80

-40

-60

-20

-100

Po

wer

[dB

m]

0 0.2 0.80.4 0.6 1Frequency [MHz] Frequency [MHz]

Conventional method Proposed method

Fundamental

(200kHz) : 3.8 dBm

HD3

(600kHz) : -60 dBm

2.6 dBm

-74 dBm

0 0.2 0.80.4 0.6 1

-1.2 dB

-14 dB

Two-tone Signal

19

0

-80

-40

-60

-20

-100

Po

wer

[dB

m]

0 0.2 0.80.4 0.6 1Frequency [MHz] Frequency [MHz]

Conventional method Proposed method

0 0.2 0.80.4 0.6 1

IMD3

Fundamental

(200kHz) : 0.8 dBm

HD3

(600kHz) : -17 dBm

-0.5 dBm

-60 dBm

-1.3 dB

-43 dB

Outline

• Research Purpose

• ADC Testing Signal Generation with ΣΔADC

• Conventional Test Method

• Proposed Test Method

• Experimental Results

• Conclusion20

Conclusion

• Low-distortion sinewave generation using ΣΔ DAC

Single-tone : HD3 cancellation

Two-tone : IMD3 cancellation

• Only DSP programming change

• No need for DAC nonlinearity identification

• Effectiveness is verified with theoretical analysis

and experiments

21

22

appendix

ΣΔDAC & NyquistDAC

23

14bit

DAC

4bit

DACDigital ΣΔ

converter

14bit

14bit

4bit

Nyquist sampling

Over sampling（high speed sampling）

High resolution

Low resolution

Using time resolution

AWG by ΣΔDAC

24

Wave form

memory

Digital ΣΔ

converter

DSP

+ DAC

ΣΔDAC

fout

fs

fout＜＜fs

Resolution up

High speed AWG

（fs Resolution ）especially effective

AWG

Even Harmonics Cancellation by Differential

25

ΔY=Y1-Y2

X=Asin(2πfint)

ffin

ΔY

Y1

Y2

fin 2fin 3fin 4finf

fin

2fin

3fin

4finf

fin 2fin 3fin 4finf

Y = a1X + a2X2

+ a3X3 + a4X

4

DAC

Even harmonics are cancelled by differential signals.

Focus on the third-order harmonics

Principle of Proposed Method

26

ck

Din=X1 Din=X2

ck

ΣΔ

DACDSP

Input Din Output Y

Y = aX + bX3

T T

fin fs/2-fin

f

3fin

fin fs/2-fin

f

Output YInput Din