Example of temperature compensation circuit

Temperature compensation of the high-frequency output stage

Linear positive temperature coefficient resistors are suitable for circuits that require linear detection of changes in the resistance value, such as temperature compensation within the operating temperature range. LP73 and LT73 are recommended for the general applications, and LT73V is recommended for the automotive applications.

(e.g.) Bias resistors and output load resistors for compensating
the temperature of high frequency amplifiers.

This is an example of a high frequency amplifier used for mobile radio. If the gate voltage is constant when the ambient temperature rises, Idd increases and the temperature rises further.

Therefore, LP73 and LT73 resistors with stable positive temperature coefficient, should be used in Rc to compensate the temperature.

In this circuit, when the resistance value of Rc increases due to the temperature rise, the gate voltage is deeply biased in the negative direction, and Idd tends to decrease. Then the negative feedback is applied to stabilize heat generation.

Temperature compensation for hall effect element

Hall effect elements are sensors that are sensitive to magnetic fields. It is used as a sensor in non-contact current probes, potentiometers, etc.. The GaAs type has a temperature coefficient of -600 x 10^-6 / K (max.), so it needs to be corrected.

A typical correction circuit is shown below. When a constant hall current is supplied to the hall effect element, a potential according to the strength of the magnetic field is obtained.

Then the potential is detected by a differential amplifier, and the temperature compensation can be performed by inserting LT73 that has stable temperature coefficient corresponding to the temperature coefficient of the hall element in the position of Rc. For automotive applications, LT73V is recommended.

Temperature compensation of optical pickup

Since the sensitivity of the PIN photodiode is sensitive to temperature, the temperature compensation elements LP73, LT73  for the general applications and LT73V for the automotive applications should be used for the compensation.

R1 is a resistor that applies a reverse bias to improve the response performance. R3 / (R2 + Rc) performs amplification and temperature compensation simultaneously.

The apparent T.C.R. can be lower to the smaller one by combining the temperature compensation element with other resistors in parallel or in series.

The target element and the resistor for temperature compensation should be placed close to each other to ensure the good thermal coupling.