TS1005
absence of oxygen; for example, vacuum-packaging
way to achieve this objective is to use an RC filter at
the noninverting terminal of the TS1005. If additional
attenuation is needed, a two-pole Sallen-Key filter
can be used to provide the additional attenuation as
shown in Figure 3.
of food products is one example.
The circuit in Figure
1
illustrates
a
typical
implementation used to amplify the output of an
oxygen detector. The TS1005 makes an excellent
choice for this application as it only draws 1.3µA of
supply current and operates on supply voltages
For best results, the filter’s cutoff frequency should
be 8 to 10 times lower than the TS1005’s crossover
frequency. Additional operational amplifier phase
margin shift can be avoided if the amplifier
bandwidth-to-signal bandwidth ratio is greater than
8.
The design equations for the 2-pole Sallen-Key low-
pass filter are given below with component values
selected to set a 2kHz low-pass filter cutoff
frequency:
R1 = R2 = R = 1MΩ
C1 = C2 = C = 80pF
Q = Filter Peaking Factor = 1
f–3dB = 1/(2 x π x RC) = 2kHz
R3 = R4/(2-1/Q); with Q = 1, R3 = R4.
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 1.4μA 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
TS1005, such as its low offset voltage, low TCVOS,
low input bias current, high CMRR, and high PSRR
are other factors which make the TS1005 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
TS1005 can operate from a conventionally-available
single 1.5-V alkaline AA battery for over 145 years!
At such low power consumption from a single cell,
the oxygen sensor could be replaced over 75 times
before the battery requires replacing!
A
Single +1.5
V
Supply, Two Op Amp
Instrumentation Amplifier
The TS1005’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.
Figure 4: A Two Op Amp Instrumentation Amplifier.
MicroWatt, Buffered Single-pole Low-Pass Filters
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
noninverting amplifier as shown in the figure.
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 2: A Simple, Single-pole Active Low-Pass Filter.
Figure 3: A Micropower 2-Pole Sallen-Key Low-Pass Filter.
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