Differential Thermometer (Continued)
Temperature Scanner
In some applications it is important to monitor several tem-
peratures periodically, rather than continuously. The circuit
shown in Figure 21 does this with the aid of an LM604 Mux
Amp. Each channel is multiplexed to the output according to
the AB channel select. The CD4060 ripple binary counter
has an on-board oscillator for continuous updating of the
channel selects.
Conclusion
As can be seen, the LM34 and LM35 are easy-to-use tem-
perature sensors with excellent linearity. These sensors can
be used with minimal external circuitry for a wide variety of
applications and do not require any elaborate scaling
schemes nor offset voltage subtraction to reproduce the
Fahrenheit and Celsius temperature scales respectively.
References
1. R.A. Pease, “A Fahrenheit Temperature Sensor”, pre-
sented at the ISSCC Conference, February 24, 1984.
2. R.A. Pease, “A New Celsius Temperature Sensor”, Na-
tional Semiconductor Corp., 1983.
3. Robert Dobkin, “Monolithic Temperature Transducer”, in
Dig. Tech. Papers, Int. Solid State Circuits Conf., 1974,
pp. 126, 127, 239, 240.
4. Gerard C.M. Meijer, “An IC Temperature Sensor with an
Intrinsic Reference”, IEEE Journal of Solid State Cir-
cuits, VOL SC-15, June 1980, pp. 370–373.
5. R.J. Widlar, “An Exact Expression for the Thermal Varia-
tion of the Emitter — Base Voltage of Bipolar Transis-
tors”, Proc. IEEE, January 1967.
6. Y.P. Tsividis, “Accurate Analysis of Temperature Effects
in I
C
−V
BE
Characteristics with Application to Bandgap
Reference Sources”, IEEE Journal of Solid-State Cir-
cuits, December 1980, pp. 1076–1084.
7. Michael P. Timko, “A Two-Terminal IC Temperature
Transducer”, IEEE Journal of Solid-State Circuits, De-
cember 1976, pp. 784–788.
00905121
Temperature monitoring
If Q
4
and Q
5
are used with R = 13k and C = 510 pF the rate will be 10 kHz.
FIGURE 21.
AN-460
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