
REV. 0
AD9873
–32–
5
6
4
3
2
7
8
9
10
1
11
12
16
17
15
14
13
18
19
20
21
22
23
24
25
26
27
28
29
30
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
3
3
76
75
77
78
79
74
73
72
71
70
69
80
65
64
66
67
68
63
62
61
60
59
58
57
56
55
54
53
52
51
1
9
9
9
9
9
9
9
9
9
9
8
8
8
8
8
8
8
8
8
MQFP
TOP VIEW
(Pins Down)
V
A
I
I
–
A
A
R
R
A
A
I
I
–
A
A
R
R
A
A
Q
Q
–
T
T
D
D
P
P
R
D
D
D
S
C
S
S
D
D
P
R
F
A
AGND IQ
I IN+
I IN
–
AGND IQ
REFT8
REFB8
AGND IQ
AVDD IQ
DRVDD
REF CLK
DRGND
DGND SD
SDELTA0
SDELTA1
DVDD SD
CA_ENABLE
CA DATA
CA CLK
DVDD OSC
OSCIN
XTAL
DGND OSC
AGND PLL
PLL FILTER
AVDD PLL
DVDD PLL
DGND PLL
AVDD Tx
Tx+
Tx
–
DRGND
DRVDD
(MSB) IF(11)
IF(10)
IF(9)
IF(8)
IF(7)
IF(6)
IF(5)
IF(4)
IF(3)
IF(2)
IF(1)
IF(0)
(MSB) Rx IQ(3)
Rx IQ(2)
Rx
IQ(1)
Rx
IQ(0)
Rx
SYNC
DRGND
DRVDD
MLCK
DVDD
DGND
Tx
SYNC
(MSB) Tx
IQ(5)
Tx
IQ(4)
Tx
IQ(3)
Tx
IQ(2)
AD9873
AVDD
0.1 F
10 F
0.01 F
0.1 F 0.01 F
0.01 F
0.1 F
0.1 F
0.1 F
10 F
0.01 F
10 F
0.1 F
0.1 F
10 F
0.1 F
0.1 F
0.1 F
0.1 F
10 F
0.1 F
0.1 F
EXTERNAL
POWER SUPPLY
DECOUPLING
DGND
Tx
GND
OSC
GND
AGND IQ
AGND
V
AS
V
DS
V
DR
0.1 F
0.1 F
10 F
0.1 F
10 F
Figure 24. Power Supply Decoupling
POWER AND GROUNDING CONSIDERATIONS
In systems seeking to simultaneously achieve high speed and high
performance, the implementation and construction of the printed
circuit board design is often as important as the circuit design.
Proper RF techniques must be used in device selection, placement,
routing, supply bypassing, and grounding. Figure 24 illustrates
proper power supply decoupling. Split-ground technique can
be used to isolate digital and high-speed clock generation noise
from the analog front ends. The analog front end may be
further split to minimize crosstalk between the transmit and
receive sections. Noise-sensitive video-IF signals can also be
separated from the more robust IQ-ADC signal path. One com-
mon ground underneath the chip connects all ground splits and
assures short distances for ground pin connections. Figure 24
uses two separate power supplies. V
AS
powers the analog and
clock generation section of the chip while V
DS
is used for the
digital signals of the chip. An extra power supply V
DR
is only
needed in applications that require lower level digital outputs.
D
RVDD
and D
VDD
pins should be connected together for normal
mode. V
DS
(and V
DR
) should not be directly connected to the
power supply of noisy digital signal processing chips. It might
even be considered as an analog supply. Ferrite beads and 10 F
decoupling capacitors isolate power supplies between functional
blocks. Each supply pin is further decoupled with a 0.1 F multi-
layer ceramic capacitor that is mounted as close as possible to
the pin. In the high-speed PLL and DAC sections additional
0.01
F capacitors may be required as shown in Figure 24.