AD8302ARU-REEL Analog Devices Inc, AD8302ARU-REEL Datasheet - Page 20

• Manufacturer Part Number: AD8302ARU-REEL
• Description: IC DETECTOR RF/IF 14-TSSOP T/R
• Manufacturer: Analog Devices Inc

Specifications of AD8302ARU-REEL

• Rohs Status: RoHS non-compliant
• Frequency: 2.7GHz
• Rf Type: General Purpose
• Input Range: -60dBm ~ 0dBm
• Accuracy: 0.5dB
• Voltage - Supply: 2.7 V ~ 5.5 V
• Current - Supply: 23mA
• Package / Case: 14-TSSOP (0.173", 4.40mm Width)
• Pin Count: 14
• Screening Level: Industrial
• Package Type: TSSOP
• Lead Free Status / Rohs Status: Not Compliant

AD8302
Reflectometer
The AD8302 can be configured to measure the magnitude ratio
and phase difference of signals that are incident on and reflected
from a load. The vector reflection coefficient, , is defined as,
where Z
teristic system impedance.
The measured reflection coefficient can be used to calculate the
level of impedance mismatch or standing wave ratio (SWR) of a
particular load condition. This proves particularly useful in diag-
nosing varying load impedances such as antennas that can degrade
performance and even cause physical damage. The vector
reflectometer arrangement given in Figure 13 consists of a pair
of directional couplers that sample the incident and reflected sig-
nals. The attenuators reposition the two signal levels within the
dynamic range of the AD8302. In analogy to Equations 15 and
16, the attenuation factors and coupling coefficients are given by:
where
negative for passive loads. Consider the case where the incident
signal is 10 dBm and the nominal reflection coefficient is –19 dB.
As shown in Figure 13, using 20 dB couplers on both sides and
–30 dBm for P
are 1 dB and 20 dB, respectively. The magnitude and phase of
the reflection coefficient are available at the VMAG and VPHS
pins scaled to 30 mV/dB and 10 mV/degree. When
the VMAG output is 900 mV.
Γ =
C
C
B
Re
A
+
+
flected Voltage / Incident Voltage
L
NOM
L
L
is the complex load impedance and Z
B
A
=
=
is the nominal reflection coefficient in dB and is
P
P
OPT
IN
IN
, the attenuators for Channel A and B paths
−
+
P
Γ
OPT
NOM
−
P
OPT
=
(
Z
L
−
Z
O
O
)
/ Z
is the charac-
(
L
is –19 dB,
+
Z
O
)
(18)
(19)
(17)
–20–
The measurement accuracy can be compromised if board
level details are not addressed. Minimize the physical distance
between the series connected couplers since the extra path
length adds phase error to . Keep the paths from the couplers
to the AD8302 as well matched as possible since any differences
introduce measurement errors. The finite directivity, D, of the
couplers sets the minimum detectable reflection coefficient, i.e.,
|
Γ
MIN
Figure 13. Using the AD8302 to Measure the Vector
Reflection Coefficient Off an Arbitrary Load
SOURCE
(dB)|<|D(dB)|.
INCIDENT
WAVE
C3
C5
R2
C6
20dB
1
2
3
4
5
6
7
COMM
INPA
OFSA
VPOS
OFSB
INPB
COMM
AD8302
C4
1dB
R1
C1
VMAG
MSET
MFLT
VREF
VPHS
PSET
PFLT
REFLECTED
14
13
12
11
10
R4
9
8
C2
WAVE
C8
C7
R5
R6
VP
Z
REV. A
LOAD