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參數資料
| 型號： | AD8307 |
| 廠商： | Analog Devices, Inc. |
| 元件分類： | 運動控制電子 |
| 英文描述： | Low Cost DC-500 MHz, 92 dB Logarithmic Amplifier(對數放大器) |
| 中文描述： | 低成本DC - 500兆赫，九十二分貝對數放大器（對數放大器） |
| 文件頁數： | 11/20頁 |
| 文件大小： | 303K |
| 代理商： | AD8307 |
AD8307
–11–
REV. 0
PRODUCT OVE RVIE W
T he AD8307 comprises six main amplifier/limiter stages, each
having a gain of 14.3 dB and small signal bandwidth of 900 MHz;
the overall
gain is 86 dB with a –3 dB bandwidth of 500 MHz.
T hese six cells, and their associated g
m
-styled full-wave detec-
tors, handle the lower two-thirds of the dynamic range. T hree
top-end detectors, placed at 14.3 dB taps on a passive attenua-
tor, handle the upper third of the 90 dB range. Biasing for these
cells is provided by two references: one determines their gain;
the other is a bandgap circuit that determines the logarithmic
slope and stabilizes it against supply- and temperature-variations.
T he AD8307 may be enabled/disabled by a CMOS-compatible
level at ENB (Pin 6). T he first amplifier stage provides a low
voltage noise spectral density (1.5 nV/
√
Hz
).
T he differential current-mode outputs of the nine detectors are
summed and then converted to single-sided form in the output
stage, nominally scaled 2
μ
A/dB. T he logarithmic output voltage
is developed by applying this current to an on-chip 12.5 k
resistor, resulting in a logarithmic slope of 25 mV/dB (i.e.,
500 mV/decade) at OUT . T his voltage is not buffered, allowing
the use of a variety of special output interfaces, including the
addition of post-demodulation filtering. T he last detector stage
includes a modification to temperature-stabilize the log intercept,
which is accurately positioned to make optimal use of the full
output voltage range available. T he intercept may be adjusted
using the pin INT , which adds or subtracts a small current to
the signal current.
BAND GAP REFERENCE
AND BIASING
SIX 14.3dB 900MHz
AMPLIFIER STAGES
MIRROR
INPUT– OFFSET
COMPENSATION LOOP
COMMON
–INPUT
+INPUT
SUPPLY
ENABLE
INT. ADJ
OUTPUT
OFS. ADJ.
AD8307
7.5mA
1.1k
V
3
2
2
m
A
/dB
12.5k
V
COM
NINE DETECTOR CELLS
SPACED 14.3dB
INT
ENB
OUT
OFS
COM
INM
INP
VPS
COM
Figure 25. Main Features of the AD8307
T he last gain stage also includes an offset-sensing cell. T his
generates a bipolarity output current when the main signal path
has an imbalance due to accumulated dc offsets. T his current is
integrated by an on-chip capacitor (which may be increased in
value by an off-chip component, at OFS). T he resulting voltage
is used to null the offset at the output of the first stage. Since it
does not involve the signal input connections, whose ac coupling
capacitors otherwise introduce a second pole in the feedback
path, the stability of the offset correction loop is assured.
T he AD8307 is built
on an advanced dielectrically-isolated
complementary bipolar process.
Most resistors are thin-film
types having a low temperature coefficient of resistance (T CR)
and high linearity under large signal conditions. T heir absolute
tolerance will typically be within
±
20%. Similarly, the capacitors
have a typical tolerance of
±
15% and essentially zero tempera-
ture or voltage sensitivity. Most interfaces have additional small
junction capacitances associated with them, due to active
devices or ESD protection; these may be neither accurate nor
stable. Component numbering in each of these interface dia-
grams is local.
E nable Interface
T he chip-enable interface is shown in Figure 26. T he currents
in the diode-connected transistors control the turn-on and turn-
off states of the bandgap reference and the bias generator, and
are a maximum of 100
μ
A when Pin 6 is taken to 5 V, under
worst case conditions. Left unconnected, or at a voltage below
1 V, the AD8307 will be disabled and consume a sleep current
of under 50
μ
A; tied to the supply, or a voltage above 2 V, it will
be fully enabled. T he internal bias circuitry is very fast (typically
<100 ns for either OFF or ON), and in practice the latency
period before the log amp exhibits its full dynamic range is more
likely to be limited by factors relating to the use of ac coupling
at the input or the settling of the offset-control loop (see follow-
ing sections).
COM
ENB
40k
V
TO BIAS
STAGES
AD8307
Figure 26. Enable Interface
TOP-END
DETECTORS
COM
INP
INM
C
P
C
D
C
M
COM
4k
V
~3k
V
125
V
6k
V
6k
V
2k
V
TYP +2.2V FOR
+3V SUPPLY,
+3.2V AT +5V
S
S
VPS
COM
I
2.4mA
Q1
Q2
Figure 27. Signal Input Interface
Input Interface
Figure 27 shows the essentials of the signal input interface. C
P
and C
M
are the parasitic capacitances to ground; C
D
is the dif-
ferential input capacitance, mostly due to Q1 and Q2. In most
applications both input pins are ac-coupled. T he switches S
close when Enable is asserted. When disabled, the inputs float,
bias current I
E
is shut off, and the coupling capacitors remain
charged. If the log amp is disabled for long periods, small leak-
age currents will discharge these capacitors. If they are poorly
matched, charging currents at power-up can generate a transient
input voltage which may block the lower reaches of the dynamic
range until it has become much less than the signal.
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相關代理商/技術參數 |
參數描述 |
|---|---|
| AD8307_06 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Low Cost DC-500 MHz, 92 dB Logarithmic Amplifier |
| AD8307AN | 功能描述:IC LOGARITHMIC AMP 8-DIP RoHS:否 類別:集成電路 (IC) >> 線性 - 放大器 - 專用 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:60 系列:- 類型:可變增益放大器 應用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤 供應商設備封裝:20-TQFN-EP（5x5） 包裝:托盤 |
| AD8307ANZ | 功能描述:IC LOGARITHMIC AMP 8-DIP RoHS:是 類別:集成電路 (IC) >> 線性 - 放大器 - 專用 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:60 系列:- 類型:可變增益放大器 應用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤 供應商設備封裝:20-TQFN-EP（5x5） 包裝:托盤 |
| AD8307AR | 功能描述:IC LOGARITHMIC AMP 92DB 8-SOIC RoHS:否 類別:集成電路 (IC) >> 線性 - 放大器 - 專用 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:60 系列:- 類型:可變增益放大器 應用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤 供應商設備封裝:20-TQFN-EP（5x5） 包裝:托盤 |
| AD8307AR-REEL | 功能描述:IC LOGARITHMIC AMP 8-SOIC T/R RoHS:否 類別:集成電路 (IC) >> 線性 - 放大器 - 專用 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:60 系列:- 類型:可變增益放大器 應用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤 供應商設備封裝:20-TQFN-EP（5x5） 包裝:托盤 |
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