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| 型號： | ADL5304ACPZ-R7 |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 10/32頁 |
| 文件大小： | 0K |
| 描述： | IC AMP LOG CONV 32LFCSP |
| 標(biāo)準(zhǔn)包裝： | 1 |
| 類型： | 對數(shù)轉(zhuǎn)換器 |
| 應(yīng)用： | 光纖 |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 32-VFQFN 裸露焊盤，CSP |
| 供應(yīng)商設(shè)備封裝： | 32-LFCSP-VQ（5x5） |
| 包裝： | 標(biāo)準(zhǔn)包裝 |
| 其它名稱： | ADL5304ACPZ-R7DKR |
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ADL5304
Data Sheet
Rev. 0 | Page 18 of 32
Decibel Scaling
When signal power is expressed in decibels above a reference level
(for example, dBm, when the reference is 1 mW), logarithmic
conversion has already been implicitly performed. Therefore, the
log ratio in the previous expressions becomes a simple difference.
Be careful in assigning variable names, because P is often used to
denote actual power as well as this same power expressed in
decibels. These are very different quantities. Misunderstandings
can be avoided by using D to denote decibel powers.
When VY (the volts/decade ) is converted to its decibel value,
= VY/10 (because there are 10 dB per decade in the context
of a power measurement), it can be written
′
Y
V
VLOG = 20 mV(DOPT DZ)
(13)
where:
DOPT is the optical power expressed in decibels above a reference
level.
DZ denotes the equivalent intercept power relative to the same level.
Using the previous example and assuming a reference power
of 1 mW, a POPT of 12.5 μW corresponds to a DOPT of
10 log10(12.5 μW/1 mW) = 19.03 dBm; the equivalent intercept
power of 3.95 fW corresponds to a DZ of 114.03 dBm. Therefore,
VLOG = 20 mV{19.03 (114.03)} = 1.900 V
(14)
the same result calculated with Equation 12.
CIRCUIT DESCRIPTION
The ADL5304 addresses a wide variety of interfacing conditions
to meet the needs of fiber optic supervisory systems, as well as
many nonoptical applications. This section explains the general
structure of this log amp. The ADL5304 is an order of magnitude
faster than any previous log amp that Analog Devices, Inc., has
made, through careful FET amp design; the key limitation in
the speed at low currents.
Figure 45 is a simplified schematic of the front-end section of
INUM pin. The voltage at this node is equal to that on the two
adjacent guard pins, VSM2 and IDEN, differing only by the offset
voltage of the JFET op amp that supports the operation of the
Translinear Device Q1 that converts the INUM current to a
logarithmic voltage. VSM2 is needed to provide the collector-
emitter bias for Q1, and it is preset to 1.5 V via the external
connection to Pin 1P5V.
094
59-
055
MONITOR AND
PD BIAS
(1.1× INUM)
2
3
4
5
6
8
7
30
31
26
VSM1
VSM2
RMNTR
32
VSM4
VSM3
IREF
IDEN
INUM
100nA
Q2
Q1
Q3
1.5V
10
9
VDEN
INDN
VNUM
IMON
INNM
1P5V
1.5V
VREF
TEMP
COMP
VNUM
ILOG
VDEN
SHIELD
PD
Figure 45. Simplified Front-End Schematic
In conventional translinear log amps, the collector and base of
Q1 are both held at ground potential, this is not possible in a
single-supply part.
A second transistor, Q2, operates at a collector current of IDEN.
In most applications, this is the reference of IREF = 100 nA,
supplied internally and laser trimmed.
The difference between the two VBEs with Q1 accepting a
photodiode current of INUM = IPD is
VBE1 VBE2 = VT log10(IPD/IREF)
(15)
By adding an accurate PTAT voltage of magnitude,
VOFS = VT log10(IREF/IZ) = 1.500 V
(16)
resulting in
VBE1 VBE2 + VOFS = VT [log10(IPD/IREF) + log10(IREF/IZ)]
= (kT/q) log10(IPD/IZ)
(17)
The temperature variation of kT/q is then eliminated by an
analog divider that essentially puts a variable proportional to
temperature underneath the T in Equation 17 and raising the
magnitude of kT/q to a stable value of 0.2 V. Therefore, for
photodiode applications,
VLOG = 0.2 V log10(IPD/IZ)
(18)
When the VSM1to VSM4, DCBI, and INPS pins are tied to
ground and VNEG < 2 V, the offset (VOFS) is removed, leaving
the more general form.
VLOG = 0.2 V log10(INUM/IDEN)
(19)
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| ADL5304ACPZ-RL | 功能描述:IC AMP LOG CONV 32LFCSP RoHS:是 類別:集成電路 (IC) >> 線性 - 放大器 - 專用 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:60 系列:- 類型:可變增益放大器 應(yīng)用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:20-TQFN-EP（5x5） 包裝:托盤 |
| ADL5304-EVALZ | 功能描述:BOARD EVAL FOR ADL5304A RoHS:是 類別:編程器，開發(fā)系統(tǒng) >> 評估演示板和套件 系列:* 標(biāo)準(zhǔn)包裝:1 系列:- 主要目的:電信，線路接口單元（LIU） 嵌入式:- 已用 IC / 零件:IDT82V2081 主要屬性:T1/J1/E1 LIU 次要屬性:- 已供物品:板，電源，線纜，CD 其它名稱:82EBV2081 |
| ADL5305ACP-REEL | 制造商:Analog Devices 功能描述:LOGARITHMIC CONVERTER - Tape and Reel |
| ADL5306 | 制造商:AD 制造商全稱:Analog Devices 功能描述:60 dB Range (100 nA to 100 UA) Low Cost Logarithmic Converter |
| ADL5306ACP | 制造商:AD 制造商全稱:Analog Devices 功能描述:60 dB Range (100 nA to 100 UA) Low Cost Logarithmic Converter |
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