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

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

1.3

Nyquist Theorem Limits Frequency Bandwidth

1.4

Ping-Pong ADCSArchitecture

1.5

Ping-Pong ADCSRaw Spectral Response

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

1.7

Advanced Filter Bank (AFB)Reduces Spurs Due to ADC Mismatch

1.8

Ping Pong ADCsTrimmed SFDR

1.9

Ping Pong ADCsTemperature Effects

1.10

Linear Error Compensation (LinComp)Corrects for Non-Linearities

1.11

Driving ADCsReferences

Analog Dialogue 39-4 (April 2005)

Analog-Digital Conversion Seminar (2004)

1.12

Transformer Coupling Gives Best High Frequency Performance

1.13

ADC Drive

1.14

Dual Transformers Improve Balance at High Frequencies

1.15

Baluns Have a Wider Frequency Response

1.16

Applying Voltage Gain Can Improve Noise Performance

1.17

DACsSome Things You May Not Have Thought Of

Sinc Compensation Effects

Glitch Energy

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

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

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

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

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

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

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

1.25

Things They Don’t Teach You In School

Watch ALL your inputs

Proper Decoupling

Differential Signaling

Clean Your Clock

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

1.27

Power Supply Decoupling Must Be Effective at Very High Frequencies

PROPER DECOUPLING NO DECOUPLING

VERTICAL SCALES: 10dB/div, HORIZONTAL SCALES: 10MHz/div

1.28

Why Differential Signaling?

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

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