AD8313ARM Analog Devices Inc, AD8313ARM Datasheet - Page 17

IC LOGARTIHMIC AMP 70DB 8-MSOP

AD8313ARM

Manufacturer Part Number
AD8313ARM
Description
IC LOGARTIHMIC AMP 70DB 8-MSOP
Manufacturer
Analog Devices Inc
Type
Logarithmic Ampr
Datasheet

Specifications of AD8313ARM

Rohs Status
RoHS non-compliant
Frequency
100MHz ~ 2.5GHz
Rf Type
RADAR, 802.11/Wi-Fi, 8.2.16/WiMax, Wireless LAN
Input Range
-65dBm ~ 0dBm
Accuracy
±1dB
Voltage - Supply
2.7 V ~ 5.5 V
Current - Supply
13.7mA
Package / Case
8-TSSOP, 8-MSOP (0.118", 3.00mm Width)
Number Of Channels
1
Number Of Elements
8
Power Supply Requirement
Single
Voltage Gain Db
84dB
Input Resistance
0.0009@5VMohm
Input Bias Current
10@5VnA
Single Supply Voltage (typ)
3/5V
Dual Supply Voltage (typ)
Not RequiredV
Power Dissipation
200mW
Rail/rail I/o Type
Rail to Rail Output
Single Supply Voltage (min)
2.7V
Single Supply Voltage (max)
5.5V
Dual Supply Voltage (min)
Not RequiredV
Dual Supply Voltage (max)
Not RequiredV
Operating Temp Range
-40C to 85C
Operating Temperature Classification
Industrial
Mounting
Surface Mount
Pin Count
8
Package Type
MSOP
Lead Free Status / RoHS Status
Not Compliant

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Typically, the AD8313 needs to be matched to 50 Ω. The input
impedance of the AD8313 at 100 MHz can be read from the
Smith chart (Figure 26) and corresponds to a resistive input
impedance of 900 Ω in parallel with a capacitance of 1.1 pF.
To make the matching process simpler, the AD8313 input cap-
acitance, C
by adding a virtual shunt inductor (L2), which resonates away
C
later. This allows the main calculation to be based on a simple
resistive-to-resistive match, that is, 50 Ω to 900 Ω.
The resonant frequency is defined by the equation
therefore,
With C
on matching a 50 Ω source resistance to a (purely resistive) load
of 900 Ω and calculating values for C
the input looks purely resistive at a frequency given by
Solving for C
IN
(Figure 36). This inductor is factored back into the calculation
50Ω SOURCE
50Ω SOURCE
ω
C
L2
R
f
0
S
=
IN
MATCH
R
=
=
and L2 temporarily out of the picture, the focus is now
IN
2
ω
IN
L2 ×
π
2
, can be temporarily removed from the calculation
=
MATCH
50Ω
50Ω
1
C
1
C
L1
=
IN
Figure 35. Narrow-Band Reactive Match
C
MATCH
IN
Figure 36. Input Matching Example
×
L1
=
1
R
gives
C
2
S
1
MATCH
3 .
R
C
L
IN
µ
MATCH
MATCH
H
C1
C2
×
C1
C2
2
=
=
=
π
(C1 × C2)
(C1 + C2)
(C1 × C2)
(C1 + C2)
1
100
f
0
L1
=
L
MHz
MATCH
7
5 .
MATCH
INDUCTANCE
pF
L2
TEMPORARY
and L1. When
AD8313
AD8313
C
C
IN
IN
R
R
IN
IN
Rev. D | Page 17 of 24
Solving for L1 gives
Because L1 and L2 are parallel, they can be combined to give the
final value for L
C1 and C2 can be chosen in a number of ways. First, C2 can be
set to a large value, for example, 1000 pF, so that it appears as an
RF short. C1 would then be set equal to the calculated value of
C
so that the total series capacitance is equal to C
C1 and C2 slightly unequal (that is, select C2 to be about 10%
less than C1) but keeping their series value the same, the ampli-
tude of the signals on INHI and INLO can be equalized so that
the AD8313 is driven in a more balanced manner. Any of the
options detailed above can be used provided that the combined
series value of C1 and C2, that is, C1 × C2/(C1 + C2) is equal to
C
In all cases, the values of C
from standard values. At this point, these values need now be
installed on the board and measured for performance at
100 MHz. Because of board and layout parasitics, the component
values from the preceding example had to be tuned to the final
values of C
Table 4.
Assuming a lossless matching network and noting conservation
of power, the impedance transformation from R
900 Ω) has an associated voltage gain given by
Because the AD8313 input responds to voltage and not to true
power, the voltage gain of the matching network increases the
effective input low-end power sensitivity by this amount. Thus,
in this case, the dynamic range is shifted downward, that is, the
12.6 dB voltage gain shifts the 0 dBm to −65 dBm input range
downward to −12.6 dBm to −77.6 dBm. However, because of
network losses, this gain is not be fully realized in practice.
Refer to Figure 33 and Figure 34 for an example of practical
attainable voltage gains.
Table 4 shows recommended values for the inductor and cap-
acitors in Figure 35 for some selected RF frequencies in addition
to the associated theoretical voltage gain. These values for a
reactive match are optimal for the board layout detailed as
Figure 45.
MATCH
MATCH
Gain
L1
L
. Alternatively, C1 and C2 can each be set to twice C
.
MATCH
=
dB
MATCH
R
2
=
S
π
=
20
f
R
0
MATCH
IN
L1
L1
= 8.9 pF and L
×
log
+
=
×
, that is,
337
L2
L2
R
=
6 .
R
IN
S
MATCH
294
nH
=
nH
12
MATCH
and L
6 .
dB
= 270 nH as shown in
MATCH
must be chosen
MATCH
S
to R
. By making
AD8313
IN
(50 Ω to
MATCH

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