One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com
AD9129 by Corey Birdsall
The AD9129 evaluation board features filtering on the power supplies to guarantee optimal performance of the digital-toanalog converter (DAC). This application note explores the effects of removing most of the filtering components. All ferrite beads on the board were removed, as well as the majority of the capacitors on the power supplies. Phase noise, noise spectral density (NSD), spurious-free dynamic range (SFDR), intermodulation distortion (IMD), and adjacent channel leakage ratio (ACLR) performance were then all measured to demonstrate the effect of removing the filtering components.
The measurement results showed that the ferrite beads improved close-in phase noise at 20 Hz offset by approximately
5 dB, as well as single-tone IMD by up to 5 dB. Most of the capacitors proved to be redundant; these are shown as Xs in
Figure 1. The decoupling capacitors, C1 and C2, encircled in
Figure 1, improved the ACLR for 6 MHz carriers by 5 dB. The capacitor arrays, CN1 and C25, also encircled in Figure 1,
improved the ACLR for 6 MHz carriers by approximately 6 dB and the NSD by approximately 1 dB.
Removing all of the capacitors crossed out with an X in Figure 1
did not affect the performance of the DAC.
1
3
5
7
47000pF
GND
6
8
CN1
2
4
DVDD
1
3
5
7
VSSA
47000pF
6
8
C25
2
4
AVDD
C10
0.001µF
C0402
C12
0.001µF
C0402
C58
0.1µF
C0603
C60
0.1µF
C0603
1
3
5
7
47000pF
GND
DVDD
6
8
CN3
2
4
C68
0.001µF
C0402
P
N
AVDD
1
3
5
7
47000pF
GND
6
8
CN4
2
4
+5V
P3
1
2
571-0500
GND
P4
1
2
DVDD
571-0100
C45
P
4.7µF
C3528
N
C104
47µF
C7343
GND
A2
ADP3339AKCZ-1.8-RL
3
IN OUT
2
GND
1 4
OUT
C62
1µF
C0603
GND
GND
E4
1
115Ω
C17
1µF
C0603
GND
2
1
JP3
2
JPR0805
1
TP2
RED
P
N
JP1
1 2
JPR1206
1
TP12
RED
P
N
C6
22µF
C7343
1
TP3
BLK
GND
C19
22µF
C7343
1
TP9
BLK
1
115Ω
C8
0.1µF
C0402
E3
2
VDD_USB
C9
0.1µF
C0402
1
115Ω
C51
0.1µF
C0402
E1
2
DVDD
C56
0.1µF
C0402
C43
0.1µF
C0306
C50
0.1µF
C0603
C53
0.1µF
C0603
C37
0.001µF
C0402
P
N
C38
P
4.7µF
C3528
N
AVDD
C39
47µF
C7343
GND
GND
C73
U6
ADP3339AKCZ-1.8-RL
3
IN OUT
2
GND OUT
1 4
1µF
C0603
GND GND
C74
1µF
C0603
JP6
1
JPR0805
2
1
TP20
RED
P
N
GND
GND
C75
22µF
C7343
1
TP21
BLK
1
115Ω
C76
0.1µF
C0402
E6
2
AVDD
C77
0.1µF
C0402
C59
0.1µF
C0306
C61
0.1µF
C0603
–5V
P5
1
2
571-0500
C40
0.001µF
C0402
P
N
C18
C7343
22µF
P
N
GND
C41
P
4.7µF
C3528
N
AVDD
C42
47µF
C7343
C13
0.1µF
C0603
C14
0.1µF
C0603
P
N
VDD_USB
C16
4.7µF
C3528
U4
ADP3333ARMZ-2.5-RL
C21
1µF
C0603
GND
2
7
IN
SD_N
GND
3
OUT
1
GND
VSSA
E5
115Ω
1
2
C1
0.1µF
C0402
GND
AVDD
C11
1µF
C0603
C2
0.1µF
C0402
C24
C7343
22µF
P
N
GND
U1
LM337IMP/NOPB
4
2
IN1
OUT
3
IN2
ADJ
1
GND
GND
R1
120Ω
AVDD
R4
200Ω
C15
1µF
C0603
1
TP1
RED
JP2
1 2
JPR0805
C7343
22µF
C20
N
P
AVDD
1
TP10
BLK
C22
1µF
C0603
GND
JP4
1
JPR0805
2
1
TP5
RED
P
N
1
E2
2
115Ω
C3
0.1µF
C0402
C7
0.1µF
C0402
VSSA
GND
C23
22µF
C7343
GND
1
TP6
BLK
AVDD
Figure 1. Capacitors Removed from the Power Supplies
E9
1
115Ω
C30
0.1µF
C0402
2
VCC2.5
C31
0.1µF
C0402
Rev. 0 | Page 1 of 3

AN-1296
Removal of Ferrite Beads
The E1 to E6 and E9 ferrite beads were all replaced with shorts.
Because the E7 and E11 ferrite beads are parallel to the E8 and
E10 ferrite beads, the E7 and E11 ferrite beads were deemed unnecessary and were removed. The E8 and E10 ferrite beads were left in place to ensure that the AVDD and the DVDD domains power up simultaneously. Inductors can be used in place of ferrite beads; however, one or the other is needed to give a dc short, while providing radio frequency (RF) isolation.
Because AVDD and DVDD are at the same voltage, the same low dropout (LDO) regulator can power them; however, separate filtering networks and power planes are needed to ensure that the digital noise does not couple back onto the DAC output.
Replacing the ferrite beads with shorts degraded the close-in
phase noise performance slightly, as shown in Figure 2. This
measurement was taken with a maximum full-scale current of
33 mA and no digital backoff. The phase noise was measured across multiple clock frequencies, at a low output frequency of
51 MHz, and a high output frequency of 991 MHz. The phase noise degraded by approximately 5 dB within 20 Hz of the
991 MHz signal when the ferrite beads were removed. Otherwise, performance with and without the ferrite beads was similar.
–70 f
OUT
= 991MHz
–80
–90
–100 f
OUT
= 51MHz f f f
S
= 2000MHz
S
= 2200MHz f
S
= 2600MHz
S
= 2800MHz
FERRITES: FALSE
FERRITES: TRUE
–110
–120
–130
–140
1 10 100
FREQUENCY (Hz)
1k
Figure 2. Phase Noise With and Without Ferrite Beads
10k
Replacing the ferrite beads with shorts degraded single-tone
IMD by up to 5 dB. The IMD is shown at two different clock
rates, with and without the ferrite beads, in Figure 3. This
measurement was taken with a full-scale current of 28 mA and no digital backoff.
–60
–65
–70
–75
–80
–85 f f
S
=1800MHz
S
= 2200MHz
FERRITES: FALSE
FERRITES: TRUE
–90
0 200M 400M 600M 800M
FREQUENCY (Hz)
1.0G
Figure 3. IMD With and Without Ferrite Beads
1.2G
Removal of C1 and C2
The removal of C1 and C2 degraded the ACLR performance
with 6 MHz carriers by about 5 dB, as shown in Figure 4. The
ACLR performance was measured with an eight carrier, 256 quadrature amplitude modulation (QAM) signal, full-scale current of 33 mA, no digital backoff, FIR40, and a clock rate of 2.3 GHz.
The performance of the 5.25 MHz bandwidth channel on both
sides of the eight carriers is plotted in Figure 4 and Figure 5.
–56
–58 f
S
= 2305MHz
C1, C2: TRUE
C1, C2: FALSE
–60
–62
–64
–66
–68
–70
–72
–62
–64
–66
–68
–70
–72
–74
0 200M 400M 600M
OUTPUT FREQUENCY (Hz)
800M
Figure 4. ACLR Without C1 and C2, Lower 5.25 MHz
–56
1.0G
–58 f
S
= 2305MHz
C1, C2: TRUE
C1, C2: FALSE
–60
–74
0 200M 400M 600M
OUTPUT FREQUENCY (Hz)
800M 1.0G
Figure 5. ACLR Without C1 and C2, Upper 5.25 MHz Channel
Rev. 0 | Page 2 of 3

Removing capacitor arrays, CN1 and C25, degraded the NSD performance by about 1 dB, except at lower output frequencies,
as shown in Figure 6. The NSD was tested with a band-pass filter centered at 70 MHz. Figure 6 shows the performance at a
full-scale current of 28 mA, no digital backoff, and a clock rate of both 2200 MHz and 2800 MHz. The performance was also verified to be similar at other clock rates.
–154
–156
–158
–160
–162
–164
–166 f f
S
= 2200MHz
S
= 2800MHz
CAPACITOR ARRAYS: TRUE
CAPACITOR ARRAYS: FALSE
–168
0 200M 400M 600M 800M 1.0G
OUTPUT FREQUENCY (Hz)
Figure 6. NSD Without Capacitor Arrays
1.2G
1.4G
The removal of the capacitor arrays degraded the ACLR performance with 6 MHz, 256 QAM carriers by about 6 dB, as
shown in Figure 7 and Figure 8. The ACLR performance was
measured with an eight carrier, 256 QAM signal, full-scale current of 33 mA, no digital backoff, FIR40, and a clock rate of 2.3 GHz.
The performance of the 5.25 MHz bandwidth channel on both
sides of the eight carriers is plotted in Figure 7 and Figure 8.
AN-1296
–62
–64
–66 f
S
= 2305MHz
CAPACITOR ARRAYS: FALSE
CAPACITOR ARRAYS: TRUE
–68
–70
–72
–74
0 200M 400M 600M
OUTPUT FREQUENCY (Hz)
800M 1.0G
Figure 7. ACLR Without Capacitor Arrays, Lower 5.25 MHz Channel
–60
–62 f
S
= 2305MHz
CAPACITOR ARRAYS: FALSE
CAPACITOR ARRAYS: TRUE
–64
–66
–68
–70
–72
–74
0 200M 400M 600M
OUTPUT FREQUENCY (Hz)
800M 1.0G
Figure 8. ACLR Without Capacitor Arrays, Upper 5.25 MHz Channel
Removing the ferrite beads degraded the phase noise by about
5 dB, and the IMD by about 5 dB. Most of the decoupling capacitors on the AD9129 evaluation board did not demonstrate any noticeable contribution to performance and, therefore, it was concluded that they were not needed. Removing the decoupling capacitors on the negative supply, C1 and C2, degraded the ACLR by about 5 dB. Removing the capacitor arrays, CN1 and C25, degraded the NSD by about 1 dB, and the
ACLR by about 6 dB.
©2014 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
AN12133-0-6/14(0)
Rev. 0 | Page 3 of 3