OP492GS(RevB) View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
OP492GS Datasheet PDF : 20 Pages
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OP292/OP492
A Low-Cost, Linearized Thermistor Amplifier
An inexpensive thermometer amplifier circuit can be implemented
using low-cost thermistors. One such implementation is shown in
Figure 8. The circuit measures temperature over the range of
0∞C to 70∞C to an accuracy of ± 0.3∞C as the linearization circuit
works well within a narrow temperature range. However, it can
measure higher temperature but at a slightly reduced accuracy. To
achieve the aforementioned accuracy, the thermistor’s nonlinearity
must be corrected. This is done by connecting the thermistor in
parallel with the 10 k⍀ in the feedback loop of the first stage
amplifier. A constant operating current of 281 A is supplied by
the resistor R1 with the 5 V reference from the REF-195 such
that the thermistor’s self-heating error is kept below 0.1∞C.
In many cases, the thermistor is placed some distance from the
signal conditioning circuit. Under this condition, a 0.1 mF capacitor
placed across R2 will help to suppress noise pickup.
This linearization network creates an offset voltage that is cor-
rected by summing a compensating current with potentiometer P1.
The temperature dependent signal is amplified by the second
stage, producing a transfer coefficient of –10 mV/∞C at the output.
To calibrate, a precision decade box can be used in place of the
thermistor. For 0∞C trim, the decade box is set to 32.650 k⍀, and
P1 is adjusted until the circuit’s output reads 0 V. To trim the circuit
at the full-scale temperature of 70∞C, the decade box is then set
to 1.752 k⍀ and P2 is adjusted until the circuit reads –0.70 V.
RT
10k⍀NTC
15V
1.0F
REF195
1F
R1*
17.8k⍀
5V
R1*
17.8k⍀
1/2
OP292
R3
R6
10k⍀ 7.87k⍀
R4
41.2k⍀
1/2
OP292
P1
10k⍀
0؇C TRIM
R5
806k⍀
NOTES
+ = ALPHA THERMISTOR 13A1002-C3
* = 0.1% IMPERIAL ASTRONICS M015
ALL RESISTORS ARE 1%, 25 ppm/؇C
EXCEPT R5 = 1%, 100 ppm/؇C
P2
200⍀
70؇C TRIM
VOUT
؊10mV/ ؇C
Figure 8. A Low Cost Linearized Thermistor Amplifier
A Single-Supply Ultrasonic Clamping/Limiting Receiver
Amplifier
Figure 9 shows an ultrasonic receiver amplifier using the non-
linear impedance of low-cost diodes to effectively control the gain
for wide dynamic range. This circuit amplifies a 40 kHz ultrasonic
signal through a pair of low-cost clamping amplifiers before feeding
a band-pass filter to extract a clean 40 kHz signal for processing.
The signal is ac-coupled into the false-ground bias node by virtue of
the capacitive piezoelectric sensing element. Rather than using
an amplifier to generate a supply splitting bias, the false ground
voltage is generated by a low-cost resistive voltage divider.
Each amplifier stage provides ac gain while passing on the dc self-
bias. As long as the output signal at each stage is less than a diode’s
forward voltage, each amplifier has unrestricted gain to amplify
low level signals. However, as the signal strength increases, the
feedback diodes begin to conduct, shunting the feedback current,
and thus reducing the gain. Although distorting the waveform,
the diodes effectively maintain a relatively constant amplitude even
with large signals that otherwise would saturate the amplifier. In
addition, this design is considerably more stable than the feed-
back type AGC.
The overall circuit has a gain range from –2 to –400, where the
inversion comes from the band-pass filter stage. Operating with
a Q of 5, the filter restores a clean, undistorted signal to the out-
put. The circuit also works well with 5 V supply systems.
12V
600k⍀
12V
RECEIVER
1/4
1M⍀ OP492
7.5V
PANASONIC
EFR-RTB40K2
12V
1/4
OP492
14k⍀ 68pF
390k⍀
10k⍀
0.01F
100k⍀
10k⍀
0.01F
6.04k⍀
0.01F
68pF
56.2k⍀
1/4
OP492
VOUT
12V
600k⍀
7.5V
1F
1M⍀
Figure 9. A 40 kHz Ultrasonic Clamping/Limiting Receiver
Amplifier
Precision Single-Supply Voltage Comparator
The OP292/OP492 have excellent overload recovery characteris-
tics, making them suitable for precision comparator applications.
Figure 10 shows the saturation recovery characteristics of the
OP492. The amplifier exhibits very little propagation delay.
The amplifier compares a signal precisely to less than 0.5 mV
offset error.
1k⍀
3Vp-p
؉15V
OP492
؊15V
1V
100
90
2k⍀
20k⍀
2.21k⍀
10
0%
5V
5µs
Figure 10. The OP492 Has Fast Overload Recovery for
Comparator Applications
Programmable Precision Window Comparator
The OP292/OP492 can be used for precise level detection such
as in test equipment where a signal is measured within a range.
Figure 11 shows such an implementation. The threshold voltage
level is set by a pair of 12-bit DIA converters. The DACs have
serial interface thus minimizing interconnection requirements.
The DAC85 12 has a control resolution of 1 mV/bit. Thus for 5 V
supply operation, maximum DAC output is 4.095 V. However,
the OP292 will accept a maximum input of 4.0 V.
–12–
REV. B
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