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参数资料
| 型号： | AD8309ARUZ-REEL7 |
| 厂商： | Analog Devices Inc |
| 文件页数： | 7/20页 |
| 文件大小： | 0K |
| 描述： | IC AMP LOG DEMODULATING 16TSSOP |
| 标准包装： | 1,000 |
| 类型： | 对数放大器 |
| 应用： | 接收器信号强度指示（RSSI） |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm 宽） |
| 供应商设备封装： | 16-TSSOP |
| 包装： | 带卷 (TR) |
REV. B
AD8309
–15–
sensitivity, but now a measure of selectively is simultaneously
introduced. Second, the component count is low: two capacitors
and an inexpensive chip inductor are needed. Third, the net-
work also serves as a balun. Analysis of this network shows that
the amplitude of the voltages at INHI and INLO are quite simi-
lar when the impedance ratio is fairly high (say, 50
to 1000 ).
1
2
3
4
5
6
7
8
VLOG
VPS2
PADL
LMHI
LMLO
PADL
FLTR
LMDR
COM2
VPS1
PADL
INHI
INLO
PADL
COM1
ENBL
AD8309
9
10
11
14
15
16
0.1 F
10
NC
RLIM
RSSI
LIMITER
OUTPUT
0.1 F
10
C2 = CM
ZIN
NC = NO CONNECT
12
13
VS
C1 = CM
LM
Figure 33. High Frequency Input Matching Network
Figure 34 shows the response for a center frequency of 100 MHz.
The response is down by 50 dB at one-tenth the center frequency,
falling by 40 dB per decade below this. The very high frequency
attenuation is relatively small, however, since in the limiting
case it is determined simply by the ratio of the AD8309’s input
capacitance to the coupling capacitors. Table I provides solu-
tions for a variety of center frequencies fC and matching from
impedances ZIN of nominally 50
and 100 . Exact values are
shown, and some judgment is needed in utilizing the nearest
standard values.
Table I.
Match to 50
Match to 100
(Gain = 13 dB)
(Gain = 10 dB)
fC
CM
LM
CM
LM
MHz
pF
nH
pF
nH
10
140
3500
100.7
4790
10.7
133
3200
94.1
4460
15
95.0
2250
67.1
3120
20
71.0
1660
50.3
2290
21.4
66.5
1550
47.0
2120
25
57.0
1310
40.3
1790
30
47.5
1070
33.5
1460
35
40.7
904
28.8
1220
40
35.6
779
25.2
1047
45
31.6
682
22.4
912
50
28.5
604
20.1
804
60
23.7
489
16.8
644
80
17.8
346
12.6
448
100
14.2
262
10.1
335
120
11.9
208
8.4
261
150
9.5
155
6.7
191
200
7.1
104
5.03
125
250
5.7
75.3
4.03
89.1
300
4.75
57.4
3.36
66.8
350
4.07
45.3
2.87
52.1
400
3.57
36.7
2.52
41.8
450
3.16
30.4
2.24
34.3
500
2.85
25.6
2.01
28.6
FREQUENCY – MHz
14
60
DECIBELS
13
12
11
10
9
8
7
6
5
70
80
90
100
110
120
130
4
3
2
1
0
–1
140
150
GAIN
INPUT AT
TERMINATION
Figure 34. Response of 100 MHz Matching Network
General Matching Procedure
For other center frequencies and source impedances, the following
method can be used to calculate the basic matching parameters.
Step 1: Tune Out CIN
At a center frequency fC, the shunt impedance of the input
capacitance CIN can be made to disappear by resonating with a
temporary inductor LIN, whose value is given by
LIN = 1/{(2 π fC)
2C
IN} = 10
10/f
C
2
(8)
when CIN = 2.5 pF. For example, at fC = 100 MHz, LIN = 1 H.
Step 2: Calculate CO and LO
Now having a purely resistive input impedance, we can calculate
the nominal coupling elements CO and LO, using
C
fR
R
L
RR
f
O
CIN
M
O
IN
M
C
=
()
= ()
1
2
π
;
(9)
For the AD8309, RIN is 1 k
. Thus, if a match to 50 is
needed, at fC = 100 MHz, CO must be 7.12 pF and LO must be
356 nH.
Step 3: Split CO Into Two Parts
Since we wish to provide the fully-balanced form of network
shown in Figure 33, two capacitors C1 = C2 each of nominally
twice CO, shown as CM in the figure, can be used. This requires
a value of 14.24 pF in this example. Under these conditions, the
voltage amplitudes at INHI and INLO will be similar. A some-
what better balance in the two drives may be achieved when C1
is made slightly larger than C2, which also allows a wider range
of choices in selecting from standard values. For example, ca-
pacitors of C1 = 15 pF and C2 = 13 pF may be used (making
CO = 6.96 pF).
Step 4: Calculate LM
The matching inductor required to provide both LIN and LO is
just the parallel combination of these:
LM = LINLO/(LIN + LO)
(10)
With LIN = 1 H and LO = 356 nH, the value of LM to complete
this example of a match of 50
at 100 MHz is 262.5 nH. The
nearest standard value of 270 nH may be used with only a slight
loss of matching accuracy. The voltage gain at resonance de-
pends only on the ratio of impedances, as is given by
GAIN
R
IN
S
IN
S
=
=
20
10
log
(11)
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