ADA4505-2ACBZ-R7 Analog Devices Inc, ADA4505-2ACBZ-R7 Datasheet - Page 17

• Manufacturer Part Number: ADA4505-2ACBZ-R7
• Description: DUAL LV 10uA CMOS OPAmp AD8506derivative
• Manufacturer: Analog Devices Inc

Specifications of ADA4505-2ACBZ-R7

• Design Resources: Precision Pulse Oximeter LED Current Sinks Using ADA4505-2, ADR1581, and ADG1636 (CN0125)
• Amplifier Type: Voltage Feedback
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Slew Rate: 0.006 V/µs
• Gain Bandwidth Product: 50kHz
• Current - Input Bias: 0.5pA
• Voltage - Input Offset: 500µV
• Current - Supply: 7µA
• Current - Output / Channel: 40mA
• Voltage - Supply, Single/dual (±): 1.8 V ~ 5 V, ±0.9 V ~ 2.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-WLCSP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: ADA4505-2ACBZ-R7TR

FOUR-POLE LOW-PASS BUTTERWORTH FILTER
FOR GLUCOSE MONITOR
There are several methods of glucose monitoring: spectroscopic
absorption of infrared light in the 2 μm to 2.5 μm range, reflec-
tance spectrophotometry, and the amperometric type using
electrochemical strips with glucose oxidase enzymes. The
amperometric type generally uses three electrodes: a reference
electrode, a control electrode, and a working electrode. Although
this is a very old and widely used technique, signal-to-noise
ratio and repeatability can be improved using the ADA4505-2/
ADA4505-4 family, with its low peak-to-peak voltage noise of
2.95 μV from 0.1 Hz to 10 Hz and voltage noise density of
65 nV/√Hz at 1 kHz.
CONTROL
REFERENCE
WORKING
DUPLICATE OF CIRCUIT ABOVE
3
2
Figure 54. Four-Pole Butterworth Filter That Can Be Used in a Glucose Meter
1000pF
5MΩ
V+
V–
C1
R1
8
4
+3.3V
ADA4505-2
1
U1
1/2
22.6kΩ
R2
22.6kΩ
0.047µF
R3
Rev. B | Page 17 of 20
0.1µF
C2
C3
5
6
Another consideration is operation from a 3.3 V battery. Glucose
signal currents are usually less than 3 μA full scale; therefore,
the I-to-V converter requires low input bias current. The
ADA4505-2/ADA4505-4 family is an excellent choice because it
provides 0.5 pA typical and 2 pA maximum input bias current
at ambient temperature.
A low-pass filter with a cutoff frequency of 80 Hz to 100 Hz is
desirable in a glucose meter device to remove extraneous noise;
this can be a simple two-pole or four-pole Butterworth filter.
Low power op amps with bandwidths of 50 kHz to 500 kHz
should be adequate. The ADA4505-2/ADA4505-4 family, with
its 50 kHz GBP and 7 μA typical current consumption, meets
these requirements. A circuit design of a four-pole Butterworth
filter (preceded by a one-pole low-pass filter) is shown in Figure 54.
With a 3.3 V battery, the total power consumption of this design
is 198 μW typical at ambient temperature.
+3.3V
V+
V–
8
4
ADA4505-2
U1
1/2
7
22.6kΩ
R4
22.6kΩ
0.047µF
R5
0.1µF
C4
C5
ADA4505-2/ADA4505-4
3
2
+3.3V
V+
V–
8
4
ADA4505-2
1/2
U2
1
V
OUT