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PDF ADPD2210 Data sheet ( Hoja de datos )
| Número de pieza | ADPD2210 | |
| Descripción | Low Power Current Amplifier | |
| Fabricantes | Analog Devices | |
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Data Sheet
FEATURES
Ultralow noise, low power current amplifier
80 fA/√Hz (typical) noise floor
140 μA (typical) of supply current when active (EE = 0 μW/cm2)
100 nA (typical) of supply current in standby
Flexible output configuration
Optimized for pulsed systems
Nominal linear output: 240 μA
Space-saving 2 mm × 2 mm LFCSP package
APPLICATIONS
Photoplethysmography
Photodiode measurements
Small current pulsed amperometry
Any application requiring the ultralow noise amplification of
small currents
Ultralow Noise, Low Power
Current Amplifier
ADPD2210
FUNCTIONAL BLOCK DIAGRAM
BIAS
VCC – (2 × VBE)
POWER-DOWN
LOGIC
PWDN
10nA
OUT
IN
24 × CURRENT MIRROR
Figure 1.
GENERAL DESCRIPTION
The ADPD2210 is a low noise current amplifier designed to
allow the use of smaller photodiodes by amplifying sensor signal
currents by a factor of 24 while adding minimal noise. This
amplification provides the system sensitivity of a large photodiode
with the benefits of a smaller photodiode. A minimum linearity
of 60 dB allows accurate extraction of very small time variant
signals on top of large dc or low frequency offsets.
The ADPD2210 is optimized for pulse mode applications such
as wrist worn heart rate monitoring (HRM) or finger worn
pulse oximeter oxygen saturation (SpO2), where low power
consumption and rejection of ambient light is critical. In photodi-
ode applications, the ADPD2210 holds the sensor input to
within ±5 mV (typical) of the reference terminal, providing
near zero-bias voltage and allowing minimal dark current and
shot noise limited performance.
The ADPD2210 is designed for applications where power
conservation is critical. The ADPD2210 uses very little power,
typically 140 μA with no input to 954 μA at full scale. A power-
down pin places the ADPD2210 in standby when sensing is
inactive. This mode adds critical time for battery-powered
monitoring and can reduce battery costs in disposable applications
Using the ADPD2210 to provide sensor site amplification
reduces the effect of electromagnetic interference (EMI) in low
level wired interfaces, providing improved signal-to-noise ratio
(SNR) and rejection of interferer signals from nearby equipment.
The combination of low power, high SNR, and EMI immunity
enables low power system solutions not possible with traditional
small current sensors, such as photodiodes plus transimpedance
amplifiers (TIAs).
Rev. A
Document Feedback
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
©2015 Analog Devices, Inc. All rights reserved.
Technical Support
www.analog.com
1 page  
ADPD2210
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter
Supply Voltage, VCC
Storage Temperature Range
Operating Ambient Temperature Range
Maximum Junction Temperature
Solder Reflow Temperature (<10 sec)
Current into IN Pin
Rating
6V
−65°C to +150°C
−40°C to +85°C
150°C
260°C
1 mA
Stresses at or above those listed under Absolute Maximum
Ratings may cause permanent damage to the product. This is a
stress rating only; functional operation of the product at these
or any other conditions above those indicated in the operational
section of this specification is not implied. Operation beyond
the maximum operating conditions for extended periods may
affect product reliability.
Data Sheet
THERMAL RESISTANCE
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Table 3. Thermal Resistance
Package Type
θJA
2 mm × 2 mm LFCSP
84.4
θJC
12.32
Unit
°C/W
ESD CAUTION
Rev. A | Page 4 of 15
5 Page 
ADPD2210
TERMINOLOGY
Amperometry
Amperometry is a technique used in chemistry and biochemis-
try to detect ions in a solution by measuring very small currents
between polarized electrodes. Methods of amperometry include
direct, pulsed, and amperometric titration, where a substance
(titrate) known to react with the analyte (the substance being
measured) is added in measured quantities and the effect on the
ionic concentration of the analyte is measured.
Dark Current
Dark current is the current flowing in a photodiode with no light
incident upon the diode junction. In reversed bias operation,
the dominant source of dark current is current generated by the
bias voltage across the bulk resistance of the semiconductor
material (shunt resistance). In zero bias operation, thermal
generation of charge carriers in the depletion region becomes
the dominant source of dark current.
Linearity
Linearity is a measure of the deviation from an ideal change in
output current relative to a change in input current. Linearity is
specified as the deviation from a best straight line fit of the
amplifier current output over a specified range of input current.
Linearity is a critical specification in photoplethysmography
due to the requirement of sensing small ac signals impressed
upon large dc offsets.
Noise Equivalent Power (NEP)
Noise equivalent power is the amount of incident light power
on a photo detector, which generates a photocurrent equal to
the total noise current of the sensor, expressed as A/√Hz. The
NEP is the fundamental baseline of the detectivity of the optical
sensor.
Offset
Offset in the ADPD2210 is defined as the differential voltage
between the reference output and the input of the ADPD2210.
The ADPD2210 holds the input terminal voltage to within
±5 mV (typical) of the reference terminal.
Photoconductive Mode
Photoconductive operation of a photodiode occurs when
photons entering the silicon generate electron/hole pairs that
are swept by the electric field to the opposite terminal. These
carriers are presented at the terminals of the photodiode as a
current proportional to the luminous flux incident on the
junction of the photodiode.
Data Sheet
Photoplethysmography
Photoplethysmography uses light to measure biological functions
by sensing changes in the absorption spectra of soft tissue
caused by differences in hemoglobin volume and composition.
Common applications of photoplethysmography include
transmission SpO2 pulse oximetry and reflectance HRM.
Shot Noise
Shot noise is a statistical fluctuation in any quantized signal
such as photons of light and electrons in current. The magni-
tude of the shot noise is expressed as a root mean square (rms)
noise current. Shot noise is a fundamental limitation in photo
detectors and takes the form of
Shot noise = √(2qIPDBW)
where:
q is the charge of an electron (1.602 × 10−19 Coulomb).
IPD is the photodiode current.
BW is the bandwidth.
Static Bias
The ADPD2210 has an internal 10 nA bias that is used to linearize
the input current mirror at low input levels and prevents transient
reverse bias of the amplifier input stage. This bias is fixed and
appears on the output as a 240 nA typical offset.
Thermal (Johnson) Noise
All resistors generate a noise component based on temperature,
including the shunt resistance in a photodiode due to genera-
tion of carriers within the bulk semiconductor. The magnitude
of this generated noise current is calculated as follows:
Photodiode Thermal Noise Current = 4kTf
RSH
where:
k = 1.38 × 10−23 joules per °K. k is the Boltzmann constant.
T is the absolute temperature in degrees Kelvin (273 K = 0°C).
Δf is the noise measurement bandwidth.
RSH is the shunt resistance of the photodiode
Thermal noise generated in the bulk semiconductor outside the
depletion region of the photodiode appears as a broadband ac
signal. Thermal noise generated within the depletion region
appears as a dc current but is typically an insignificant compo-
nent of dark current relative to the bias/shunt resistance
component.
Rev. A | Page 10 of 15
11 Page | ||
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