Motore di ricerca datesheet componenti elettronici
  Italian  ▼
ALLDATASHEETIT.COM

X  

AD645KN Scheda tecnica(PDF) 7 Page - Analog Devices

Il numero della parte AD645KN
Spiegazioni elettronici  Low Noise, Low Drift FET Op Amp
Download  8 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
Produttore elettronici  AD [Analog Devices]
Homepage  http://www.analog.com
Logo AD - Analog Devices

AD645KN Scheda tecnica(HTML) 7 Page - Analog Devices

  AD645KN Datasheet HTML 1Page - Analog Devices AD645KN Datasheet HTML 2Page - Analog Devices AD645KN Datasheet HTML 3Page - Analog Devices AD645KN Datasheet HTML 4Page - Analog Devices AD645KN Datasheet HTML 5Page - Analog Devices AD645KN Datasheet HTML 6Page - Analog Devices AD645KN Datasheet HTML 7Page - Analog Devices AD645KN Datasheet HTML 8Page - Analog Devices  
Zoom Inzoom in Zoom Outzoom out
 7 / 8 page
background image
AD645
–7–
REV. B
AD645
2
3
6
8
FILTERED
OUTPUT
OPTIONAL 26Hz
FILTER
PHOTODIODE
GUARD
OUTPUT
10pF
10
9
Figure 30. The AD645 Used as a Sensitive Preamplifier
Preamplifier Applications
The low input current and offset voltage levels of the AD645 to-
gether with its low voltage noise make this amplifier an excellent
choice for preamplifiers used in sensitive photodiode applica-
tions. In a typical preamp circuit, shown in Figure 30, the out-
put of the amplifier is equal to:
VOUT = ID (Rf) = Rp (P) Rf
where:
ID = photodiode signal current (Amps)
Rp = photodiode sensitivity (Amp/Watt)
Rf = the value of the feedback resistor, in ohms.
P = light power incident to photodiode surface, in watts.
An equivalent model for a photodiode and its dc error sources is
shown in Figure 31. The amplifier’s input current, IB, will con-
tribute an output voltage error which will be proportional to the
value of the feedback resistor. The offset voltage error, VOS, will
cause a “dark” current error due to the photodiode’s finite
shunt resistance, Rd. The resulting output voltage error, VE, is
equal to:
VE = (1 + Rf/Rd) VOS + Rf IB
A shunt resistance on the order of 10
9 ohms is typical for a
small photodiode. Resistance Rd is a junction resistance which
will typically drop by a factor of two for every 10
°C rise in tem-
perature. In the AD645, both the offset voltage and drift are
low, this helps minimize these errors.
PHOTODIODE
OUTPUT
10pF
10
9
ID
OS
V
IB
Rd
50pF
Cd
Cf
Rf
Figure 31. A Photodiode Model Showing DC Error
Sources
Minimizing Noise Contributions
The noise level limits the resolution obtainable from any pream-
plifier. The total output voltage noise divided by the feedback
resistance of the op amp defines the minimum detectable signal
current. The minimum detectable current divided by the photo-
diode sensitivity is the minimum detectable light power.
Sources of noise in a typical preamp are shown in Figure 32.
The total noise contribution is defined as:
V OUT =
in2 + i f 2 + is 2
Rf
1
+ s (Cf ) Rf


2
+ en
2
1
+
Rf
Rd
1
+ s (Cd ) Rd
1
+ s (Cf ) Rf




2
Figure 33, a spectral density versus frequency plot of each
source’s noise contribution, shows that the bandwidth of the
amplifier’s input voltage noise contribution is much greater than
its signal bandwidth. In addition, capacitance at the summing
junction results in a “peaking” of noise gain in this configura-
tion. This effect can be substantial when large photodiodes with
large shunt capacitances are used. Capacitor Cf sets the signal
bandwidth and also limits the peak in the noise gain. Each
source’s rms or root-sum-square contribution to noise is ob-
tained by integrating the sum of the squares of all the noise
sources and then by obtaining the square root of this sum. Mini-
mizing the total area under these curves will optimize the
preamplifier’s overall noise performance.
PHOTODIODE
OUTPUT
10
9
50pF
iS
iS
Rd
Cd
10pF
Cf
Rf
i f
in
en
Figure 32. Noise Contributions of Various Sources
FREQUENCY – Hz
100
1k
10k
100k
10
1
10nV
100nV
1
µV
10
µV
SIGNAL BANDWIDTH
NO FILTER
WITH FILTER
e n
is &if
in
en
Figure 33. Voltage Noise Spectral Density of the Circuit of
Figure 32 With and Without an Output Filter
An output filter with a passband close to that of the signal can
greatly improve the preamplifier’s signal to noise ratio. The pho-
todiode preamplifier shown in Figure 32—without a bandpass
filter—has a total output noise of 50
µV rms. Using a 26 Hz
single pole output filter, the total output noise drops to 23
µV
rms, a factor of 2 improvement with no loss in signal bandwidth.
Using a “T” Network
A “T” network, shown in Figure 34, can be used to boost the ef-
fective transimpedance of an I to V converter, for a given feed-
back resistor value. Unfortunately, amplifier noise and offset
voltage contributions are also amplified by the “T” network
gain. A low noise, low offset voltage amplifier, such as the
AD645, is needed for this type of application.


Codice articolo simile - AD645KN

Produttore elettroniciIl numero della parteScheda tecnicaSpiegazioni elettronici
logo
Analog Devices
AD6458 AD-AD6458 Datasheet
268Kb / 12P
   GSM 3 V Receiver IF Subsystem
REV. 0
AD6458ARS AD-AD6458ARS Datasheet
268Kb / 12P
   GSM 3 V Receiver IF Subsystem
REV. 0
AD6459 AD-AD6459 Datasheet
314Kb / 12P
   GSM 3 V Receiver IF Subsystem
REV. 0
AD6459ARS AD-AD6459ARS Datasheet
314Kb / 12P
   GSM 3 V Receiver IF Subsystem
REV. 0
More results

Descrizione simile - AD645KN

Produttore elettroniciIl numero della parteScheda tecnicaSpiegazioni elettronici
logo
Analog Devices
AD545A AD-AD545A Datasheet
280Kb / 4P
   Monolithic Precision, Low Drift FET-Input Op Amp
ADA4523-1 AD-ADA4523-1 Datasheet
923Kb / 29P
   36 V, Low Noise, Zero Drift Op Amp
Rev. 0
AD795 AD-AD795_02 Datasheet
278Kb / 16P
   Low Power, Low Noise Precision FET Op Amp
REV. B
AD795 AD-AD795_15 Datasheet
276Kb / 20P
   Low Power, Low Noise Precision FET Op Amp
REV. C
AD795 AD-AD795 Datasheet
331Kb / 16P
   Low Power, Low Noise Precision FET Op Amp
REV. A
AD795 AD-AD795_09 Datasheet
276Kb / 20P
   Low Power, Low Noise Precision FET Op Amp
REV. C
logo
Microchip Technology
MCP6286 MICROCHIP-MCP6286 Datasheet
430Kb / 28P
   Low Noise, Low Power Op Amp
2009
logo
AUK corp
S4558 AUK-S4558 Datasheet
236Kb / 4P
   Low Noise Dual OP AMP
logo
Linear Technology
LT1007X LINER-LT1007X_15 Datasheet
154Kb / 1P
   Low Noise 200C Op Amp
logo
KODENSHI_AUK CORP.
S4558 KODENSHI-S4558 Datasheet
185Kb / 4P
   Low Noise Dual OP AMP
More results


Html Pages

1 2 3 4 5 6 7 8


Scheda tecnica Scarica

Go To PDF Page


Link URL




Privacy Policy
ALLDATASHEETIT.COM
Lei ha avuto il aiuto da alldatasheet?  [ DONATE ] 

Di alldatasheet   |   Richest di pubblicita   |   contatti   |   Privacy Policy   |   scambio Link   |   Ricerca produttore
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn
Indian : Alldatasheet.in  |   Mexican : Alldatasheet.com.mx  |   British : Alldatasheet.co.uk  |   New Zealand : Alldatasheet.co.nz
Family Site : ic2ic.com  |   icmetro.com