13

LMV321TP/LMV358TP/LMV324TP

40μA, 1.27MHz, Micro-Power Rail-to-Rail I/O Op Amps

www.3peakic.com.cn

REV A.02

R1

1M

Ω

R2

1M

Ω

C1

400pF

C2

400pF

R3

2M

Ω

R4

2M

Ω

12

12

-3dB

3

4

3

4

R = R = R = 1M

C = C = C = 400pF

Q = Filter Peaking Factor = 1

f

= 1/(2

) = 400

R = R /(2-1/Q) ; with Q = 1, R =R

RC

Hz





Figure 8

Portable Gas Sensor Amplifier

Gas sensors are used in many different industrial and medical applications. Gas sensors generate a current that

is proportional to the percentage of a particular gas concentration sensed in an air sample. This output current

flows through a load resistor and the resultant voltage drop is amplified. Depending on the sensed gas and

sensitivity of the sensor, the output current can be in the range of tens of microamperes to a few milli-amperes.

Gas sensor datasheets often specify a recommended load resistor value or a range of load resistors from which

to choose.

There are two main applications for oxygen sensors

– applications which sense oxygen when it is abundantly

present (that is, in air or near an oxygen tank) and those which detect traces of oxygen in parts-per-million

concentration. In medical applications, oxygen sensors are used when air quality or oxygen delivered to a patient

needs to be monitored. In fresh air, the concentration of oxygen is 20.9% and air samples containing less than

18% oxygen are considered dangerous. In industrial applications, oxygen sensors are used to detect the absence

of oxygen; for example, vacuum-packaging of food products.

The circuit in Figure 9 illustrates a typical implementation used to amplify the output of an oxygen detector.

With

the components shown in the figure, the circuit consumes less than 37

μA of supply current ensuring that small

form-factor single- or button-cell batteries (exhibiting low mAh charge ratings) could last beyond the operating life

low input bias current, high CMRR, and high PSRR are other factors which make these amplifiers excellent

choices for this application.

100 k

Ω

1%

100

Ω

1%

100 k

Ω

1%

10 M

Ω

1%

2

O

I

2

1 in Air ( 21% O )

0.7

OUT

DD

VV

I

uA





Oxygen Sensor

City Technology

4OX2

Figure 9