TS1002 datasheet(8/13 Pages) TOUCHSTONE

8 / 13 page

TS1002/TS1004

Page 8

TS1002_4DS r1p0

RTFDS

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 is one example.

The

circuit

Figure

illustrates

typical

implementation used to amplify the output of an

oxygen detector. Either amplifier makes an

excellent choice for this application as it only draws

0.6µA of supply current per amplifier and operates

on supply voltages down to 0.65V. With the

components

shown

the

figure,

the

circuit

consumes less than 0.7

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 of the oxygen sensor.

The precision specifications of these amplifiers, such

as their low offset voltage, low TCVOS, low input bias

current, high CMRR, and high PSRR are other

factors

which

make

these

amplifiers

excellent

choices for this application. Since oxygen sensors

typically exhibit an operating life of one to two years,

an oxygen sensor amplifier built around one of these

amplifiers

can

operate

from

conventionally-

available single 1.5-V alkaline AA battery for over

290 years! At such low power consumption from a

single cell, the oxygen sensor could be replaced

over 150 times before the battery requires replacing!

NanoWatt, Buffered Single-pole Low-Pass Filters

When

receiving

low-level

signals,

limiting

the

bandwidth of the incoming signals into the system is

often required. As shown in Figure 2, the simplest

way to achieve this objective is to use an RC filter at

the noninverting terminal of the amplifier.

If additional attenuation is needed, a two-pole

Sallen-Key filter can be used to provide the

additional attenuation as shown in Figure 3.

For best results, the filter

’s cutoff frequency should

be 8 to 10 times lower than the amplfier

’s crossover

frequency. Additional operational amplifier phase

margin

shift

can

avoided

the

amplifier

bandwidth-to-signal bandwidth ratio is greater than

The design equations for the 2-pole Sallen-Key low-

pass filter are given below with component values

selected to set a 400Hz low-pass filter cutoff

frequency:

R1 = R2 = R

= 1MΩ

C1 = C2 = C = 400pF

Q = Filter Peaking Factor = 1

–3dB = 1/(2 x π x RC) = 400 Hz

R3 = R4/(2-1/Q); with Q = 1, R3 = R4.

A Single +1.5 V Supply, Two Op Amp

Instrumentation Amplifier

The

amplifiers’ ultra-low supply current and ultra-low

voltage operation make them ideal for battery-

powered applications such as the instrumentation

amplifier shown in Figure 4 using a TS1002.

Figure 2: A Simple, Single-pole Active Low-Pass Filter.

Figure 3: A Nanopower 2-Pole Sallen-Key Low-Pass Filter.

Figure 1: A Nanopower, Precision Oxygen Gas Sensor

Amplifier.

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