TS1003
The circuit in Figure
1
illustrates
a
typical
implementation used to amplify the output of an
oxygen detector. The TS1003 makes an excellent
choice for this application as it only draws 0.6µA of
supply current and operates on supply voltages
If additional attenuation is needed, a two-pole
Sallen-Key filter can be used to provide the
additional attenuation as shown in Figure 3.
Figure 3: A Micropower 2-Pole Sallen-Key Low-Pass Filter.
For best results, the filter’s cutoff frequency should
be 8 to 10 times lower than the TS1003’s crossover
frequency. Additional operational amplifier phase
margin shift can be avoided if the amplifier
bandwidth-to-signal bandwidth ratio is greater than
8.
Figure 1: A Micropower, Precision Oxygen Gas Sensor
Amplifier.
down to 0.8V. With the components shown in 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 the
TS1003, such as its low offset voltage, low TCVOS,
low input bias current, high CMRR, and high PSRR
are other factors which make the TS1003 an
excellent choice for this application. Since oxygen
sensors typically exhibit an operating life of one to
two years, an oxygen sensor amplifier built around a
TS1003 can operate from a 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!
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
f–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 TS1003’s ultra-low supply current and ultra-low
voltage operation make it ideal for battery-powered
applications such as the instrumentation amplifier
shown in Figure 4.
MicroWatt, 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
Figure 4: A Two Op Amp Instrumentation Amplifier.
Figure 2: A Simple, Single-pole Active Low-Pass Filter.
The circuit utilizes the classic two op amp
instrumentation amplifier topology with four resistors
to set the gain. The equation is simply that of a
way to achieve this objective is to use an RC filter at
the noninverting terminal of the TS1003.
Page 8
TS1003DS r1p0
RTFDS
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