AN-1296: Optimizing Power Supplies for the AD9129 (Rev. 0) PDF

AN-1296
APPLICATION NOTE
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
Optimizing Power Supplies for the AD9129
by Corey Birdsall
INTRODUCTION
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.
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
Removing all of the capacitors crossed out with an X in Figure 1
did not affect the performance of the DAC.
JP3
1
DVDD
CN1
2
1
C25
2
3
4
3
4
3
4
3
4
5
6
5
6
5
6
5
6
7
7
8
47000pF
GND
8
7
47000pF
8
7
VSSA
3
1
2
571-0500
GND
P4
1
2
DVDD
IN
OUT
GND OUT
1 4
C62
1µF
C0603
8
47000pF
GND
47000pF
GND
A2
ADP3339AKCZ-1.8-RL
+5V
P3
CN4
2
1
TP2
RED
E3
1
JPR0805
AVDD
CN3
2
1
1
P
E4
1
2
C6
22µF
C7343
N
2
C12
0.001µF
C0402
C58
0.1µF
C0603
C68
0.001µF
C0402
C60
0.1µF
C0603
P
N
GND
1
2
1
TP12
RED
C50
0.1µF
C0603
C53
0.1µF
C0603
P
C37
0.001µF
C0402
N
C38 P
4.7µF
N
C3528
U6
ADP3339AKCZ-1.8-RL
3
C39
47µF
C7343
C61
0.1µF
C0603
C40
0.001µF
C0402
N
C41 P
4.7µF
N
C3528
C42
47µF
C7343
OUT
GND
C13
0.1µF
C0603
C14
0.1µF
C0603
P
N
1
C19
22µF
C7343
2
OUT
IN
7
SD_N
GND
C21
3
1µF
C0603
GND
GND
2
DVDD
C74
1µF
C0603
C56
0.1µF
C0402
C51
0.1µF
C0402
GND
E6
1
N
TP21
BLK
1
GND
2
AVDD
115Ω
C75
22µF
C7343
P
C77
0.1µF
C0402
C76
0.1µF
C0402
GND
U4
C16
4.7µF
C3528
TP20
RED
2
ADP3333ARMZ-2.5-RL
VSSA
TP9
BLK
JPR0805
GND
VDD_USB
AVDD
C59
0.1µF
C0306
IN
1
JP6
2
GND OUT
1 4
C73
1µF
C0603
GND
P
E1
1
1
GND
C9
0.1µF
C0402
C8
0.1µF
C0402
115Ω
GND
AVDD
C43
0.1µF
C0306
1
JPR1206
571-0100
C104
47µF
C7343
TP3
BLK
GND
JP1
GND
GND
N
C45 P
4.7µF
N
C3528
VDD_USB
115Ω
C17
1µF
C0603
P
C10
0.001µF
C0402
2
115Ω
1
JP4
1
1
TP5
RED
E9
2
1
JPR0805
115Ω
C22
1µF
C0603
GND
P
N
C23
22µF
C7343
GND
1
TP6
BLK
C30
0.1µF
C0402
2
VCC2.5
C31
0.1µF
C0402
AVDD
–5V
1
2
571-0500
C11
1µF
C0603
E5
P5
U1
LM337IMP/NOPB
4 IN1
2 IN2
2
1
C18
C7343
22µF
115Ω
N
P
C1
0.1µF
C0402
C2
0.1µF
C0402
N
GND
GND
TP1
RED
E2
1
2
GND
2
VSSA
JPR0805
115Ω
R1
120Ω
C15
1µF
C0603
C7343
N
22µF
C20 P
1
P
TP10
BLK
C3
0.1µF
C0402
C7
0.1µF
C0402
AVDD
GND
GND
1
3
ADJ
1
C24
C7343
22µF
1
JP2
OUT
R4
200Ω
AVDD
AVDD
Figure 1. Capacitors Removed from the Power Supplies
Rev. 0 | Page 1 of 3
12113-001
1
DVDD
AVDD
2
AN-1296
Application Note
Removal of Ferrite Beads
–60
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.
fS =1800MHz
fS = 2200MHz
WORST IMD3 (dBc)
–65
FERRITES: FALSE
FERRITES: TRUE
–70
–75
–80
–90
0
400M
600M
800M
FREQUENCY (Hz)
1.0G
1.2G
Figure 3. IMD With and Without Ferrite Beads
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.
–70
–56
fOUT = 991MHz
fS = 2305MHz
–58
–80
–90
fS = 2000MHz
fS = 2200MHz
fS = 2600MHz
fS = 2800MHz
fOUT = 51MHz
FERRITES: FALSE
FERRITES: TRUE
–100
C1, C2: TRUE
C1, C2: FALSE
–60
LOWER 5.25MHz (dBc)
PHASE NOISE (dBc/Hz)
200M
12113-003
–85
–110
–120
–62
–64
–66
–68
–70
–130
10
100
FREQUENCY (Hz)
1k
10k
–74
0
200M
400M
600M
OUTPUT FREQUENCY (Hz)
800M
1.0G
Figure 4. ACLR Without C1 and C2, Lower 5.25 MHz
Figure 2. Phase Noise With and Without Ferrite Beads
–56
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.
fS = 2305MHz
–58
C1, C2: TRUE
C1, C2: FALSE
UPPER 5.25MHz (dBc)
–60
–62
–64
–66
–68
–70
–72
–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
12113-005
1
12113-002
–140
12113-004
–72
Application Note
AN-1296
–62
Removal of Capacitor Arrays
fS = 2305MHz
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.
CAPACITOR ARRAYS: FALSE
CAPACITOR ARRAYS: TRUE
LOWER 2.5MHz (dBc)
–64
–154
–66
–68
–70
–74
–158
200M
400M
600M
800M
1.0G
OUTPUT FREQUENCY (Hz)
Figure 7. ACLR Without Capacitor Arrays, Lower 5.25 MHz Channel
–162
–60
–164
–62
fS = 2305MHz
CAPACITOR ARRAYS: TRUE
CAPACITOR ARRAYS: FALSE
–168
0
200M
400M
600M
800M 1.0G
OUTPUT FREQUENCY (Hz)
1.2G
1.4G
Figure 6. NSD Without Capacitor Arrays
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.
CAPACITOR ARRAYS: FALSE
CAPACITOR ARRAYS: TRUE
–64
–66
–68
–70
–72
–74
0
200M
400M
600M
800M
1.0G
OUTPUT FREQUENCY (Hz)
12113-008
–166
UPPER 5.25MHz (dBc)
fS = 2200MHz
fS = 2800MHz
12113-006
NSD (dBm/Hz)
0
–160
12113-007
–72
–156
Figure 8. ACLR Without Capacitor Arrays, Upper 5.25 MHz Channel
Conclusion
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.
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AN12133-0-6/14(0)
Rev. 0 | Page 3 of 3
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