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| 型號： | AD549KHZ |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 7/20頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC OPAMP GP 1MHZ LP 20MA TO99-8 |
| 標準包裝： | 1 |
| 系列： | Topgate™ |
| 放大器類型： | 通用 |
| 電路數(shù)： | 1 |
| 轉(zhuǎn)換速率： | 3 V/µs |
| 增益帶寬積： | 1MHz |
| 電流 - 輸入偏壓： | 0.075pA |
| 電壓 - 輸入偏移： | 150µV |
| 電流 - 電源： | 600µA |
| 電流 - 輸出 / 通道： | 20mA |
| 電壓 - 電源，單路/雙路(±)： | ±5 V ~ 18 V |
| 工作溫度： | 0°C ~ 70°C |
| 安裝類型： | 通孔 |
| 封裝/外殼： | TO-99-8 金屬罐 |
| 供應(yīng)商設(shè)備封裝： | TO-99-8 |
| 包裝： | 散裝 |
| 產(chǎn)品目錄頁面： | 773 (CN2011-ZH PDF) |
AD549
Rev. H | Page 15 of 20
gain that multiplies the op amp input voltage noise contribu-
tion. A single-pole filter at the output of the amplifier limits the
op amp output voltage noise bandwidth to 26 Hz, comparable
to the signal bandwidth. This greatly improves the signal-to-
noise ratio of the preamplifier (in this case, by a factor of 3).
Input current, IB, contributes an output voltage error, VE1,
proportional to the feedback resistance
VE1 = IB × RF
The input voltage offset of the op amp causes an error current
through the photodiode shunt resistance, RS
10
1
100n
10n
1
10
100
1k
10k
100k
1M
00
51
1-
0
44
FREQUENCY (Hz)
V
O
L
T
AG
E
N
O
IS
E
CO
NT
RI
BUT
IO
NS
N
O
ISE
SP
EC
T
R
A
L
D
EN
S
IT
Y
(
n
V
/
H
z)
IF AND CS, NO FILTERS
IF AND CS, WITH FILTERS
EN
CONTRIBUTION,
WITH FILTER
EN CONTRIBUTION,
NO FILTER
AD549
OPEN-LOOP GAIN
I = VOS/RS
The error current results in an error voltage (VE2) at the
amplifier output equal to
VE2 = (1 + RF/RS)VOS
Given typical values of photodiode shunt resistance (on the order
of 109 Ω), RF/RS can easily be greater than 1, especially if a large
feedback resistance is used. Also, RF/RS increases with tempera-
ture because photodiode shunt resistance typically drops by a
factor of 2 for every 10°C rise in temperature. An op amp with
low offset voltage and low drift must be used to maintain accuracy.
The AD549K offers a guaranteed maximum 0.25 mV offset
voltage and 5 mV/°C drift for very sensitive applications.
Figure 44. Spectral Density of the Photodiode Preamp Noise
Sources vs. Frequency
Photodiode Preamp Noise
Noise limits the signal resolution obtainable with the preamp.
The output voltage noise divided by the feedback resistance is
the minimum current signal that can be detected. This mini-
mum detectable current divided by the responsivity of the
photodiode represents the lowest light power that is detectable
by the preamp.
LOG RATIO AMPLIFIER
Logarithmic ratio circuits are useful for processing signals with
wide dynamic range. The 60 fA maximum input current of the
AD549L makes it possible to build a log ratio amplifier with
1% log conformance for input currents ranging from 10 pA to
1 mA, a dynamic range of 160 dB.
Noise sources associated with the photodiode, amplifier, and
spectral density vs. frequency plot of the contribution of each of
the noise sources to the output voltage noise (circuit parameters
in Figure 42 are assumed). The rms contribution of each noise
source to the total output voltage noise is obtained by
integrating the square of its spectral density function over
frequency. The rms value of the output voltage noise is the
square root of the sum of all contributions. Minimizing the total
area under these curves optimizes the resolution of the
preamplifier for a given bandwidth.
The log ratio amplifier in Figure 45 provides an output voltage
proportional to the log base 10 of the ratio of Input Current I1
and Input Current I2. Resistor R1 and Resistor R2 are provided
for voltage inputs. Because NPN devices are used in the feedback
loop of the front-end amplifiers that provide the log transfer
function, the output is valid only for positive input voltages and
input currents. The input currents set the Collector Current IC1
and Collector Current IC2 of a matched pair of log transistors,
Q1 and Q2, to develop Voltage VA and Voltage VB
VA, VB = –(kT/q)ln IC/IES
00
5
1
-04
3
A
IS
RS
CS
CF
RF
IF
EN
IN
where IES is the saturation current of the transistor.
The difference of VA and VB is taken by the subtractor section to
obtain
VC = (kT/q)ln(IC2/IC1)
VC is scaled up by the ratio of (R9 + R10)/R8, which is equal to
approximately 16 at room temperature, resulting in the output
voltage
Figure 43. Photodiode Preamp Noise Sources
VOUT = 1 V × log(IC2/IC1)
The photodiode preamp in Figure 41 can detect a signal current
of 26 fA rms at a bandwidth of 16 Hz, which, assuming a
photodiode responsivity of 0.5 A/W, translates to a 52 fW rms
minimum detectable power. The photodiode used has a high
source resistance and low junction capacitance. CF sets the
signal bandwidth with RF and also limits the peak in the noise
R8 is a resistor with a positive 3500 ppm/°C temperature coeffi-
cient to provide the necessary temperature compensation. The
parallel combination of R15 and R7 is provided to keep the gain
of the subtractor section for positive and negative inputs matched
over temperature.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD549L | 制造商:AD 制造商全稱:Analog Devices 功能描述:Ultralow Input Bias Current Operational Amplifier |
| AD549LH | 功能描述:IC OPAMP GP 1MHZ LP 20MA TO99-8 RoHS:否 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:Topgate™ 標準包裝:50 系列:- 放大器類型:J-FET 電路數(shù):2 輸出類型:- 轉(zhuǎn)換速率:3.5 V/µs 增益帶寬積:1MHz -3db帶寬:- 電流 - 輸入偏壓:30pA 電壓 - 輸入偏移:2000µV 電流 - 電源:200µA 電流 - 輸出 / 通道:- 電壓 - 電源，單路/雙路(±):7 V ~ 36 V，±3.5 V ~ 18 V 工作溫度:0°C ~ 70°C 安裝類型:通孔 封裝/外殼:8-DIP（0.300"，7.62mm） 供應(yīng)商設(shè)備封裝:8-PDIP 包裝:管件 |
| AD549LH | 制造商:Analog Devices 功能描述:OP AMP U-LOW BIAS TO-99-8 549 |
| AD549LH/+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Voltage-Feedback Operational Amplifier |
| AD549LHZ | 功能描述:IC OPAMP GP 1MHZ LP 20MA TO99-8 RoHS:是 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:Topgate™ 標準包裝:50 系列:- 放大器類型:J-FET 電路數(shù):2 輸出類型:- 轉(zhuǎn)換速率:3.5 V/µs 增益帶寬積:1MHz -3db帶寬:- 電流 - 輸入偏壓:30pA 電壓 - 輸入偏移:2000µV 電流 - 電源:200µA 電流 - 輸出 / 通道:- 電壓 - 電源，單路/雙路(±):7 V ~ 36 V，±3.5 V ~ 18 V 工作溫度:0°C ~ 70°C 安裝類型:通孔 封裝/外殼:8-DIP（0.300"，7.62mm） 供應(yīng)商設(shè)備封裝:8-PDIP 包裝:管件 |
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