US 3,978,418 A · Low frequency electro-thermal filter

Abstract

A low frequency electro-thermal filter includes a pair of thermally coupled transistorized differential amplifiers. One of the differential amplifiers comprises a pair of heater transistors and the other differential amplifier includes a pair of sensor transistors, each heater transistor and its associated sensor transistor being fabricated on a single semiconductor chip. The heater transistors in the first differential amplifier serve differentially to heat the sensor transistors in the second differential amplifier in response to an input signal. The differential heating of the second differential amplifier differentially affects the electrical parameters of the sensor transistors and tends to upset the current balance between the stages of the second differential amplifier. A feedback loop is provided around the second differential amplifier for reestablishing the current balance thereof. The feedback signal has a rate of response that is dependent on the thermal response of the thermal coupling between the two differential amplifiers, and may be monitored to provide a filtered output signal. The characteristics of the filter are determined by the thermal characteristics of the thermal coupling and by the electrical characteristics of the second differential amplifier and the feedback loop. The thermal characteristics of the thermal coupling are determined by the size, shape, thermal conductivity and thermal capacity of the semi-conductor chip forming the heater and sensor transistors and its associated substrate. The size, shape and placement of the heater and sensor transistors may be adjusted to select whether the thermal characteristics of the chip or the insulator primarily determine the thermal transfer function.

Claims25

Dependent claims

An electro-thermal filter comprising:

an electrical input terminal;
an isothermal header;
an insulating layer bonded to said header, said insulating layer having a predetermined thermal conductivity and thermal capacity;
a second layer bonded to said insulating layer, said second layer having a thermal conductivity and a thermal capacity higher than the thermal conductivity and thermal capacity of said insulating layer, the relative thermal conductivities and thermal capacities of said insulating layer and said second layer affecting the frequency characteristics of the electrothermal filter;
a differential heater electrically coupled to said input terminal having first and second heating members disposed on said second layer, said heating members being differentially coupled to each other electrically for causing the amount of heat generated by one of said heating members to be increased and the amount of heat generated by the other of said heating members to be simultaneously decreased in response to a change in an electrical signal applied to said input terminal;
a differential heat sensor having first and second electrically coupled sensing members disposed on said second layer, said first sensing member being thermally coupled to said first heating member and said second sensing member being thermally coupled to said second heating member through said second layer;
an electrical output terminal;
and
means electrically coupling said differential heat sensor to said output terminal for applying an output signal to said output terminal representative of the difference in temperature of said first and second heat sensing members.

6 more elements

An electro-thermal circuit comprising:

first and second junction transistors each having input, output, and common electrodes, said transistors being electrically coupled together to form a differential amplifier providing substantially equal voltages at said output electrodes and having substantially equal current densities flowing through respective junctions of said junction transistors;
means for applying thermal energy to one of said first and second transistor means, said thermal energy tending to make the voltages appearing at said output electrodes unequal;
a feedback circuit connected to said output electrodes and to the input electrode of said first transistor means, said feedback circuit being responsive to a difference in the voltages appearing at said output electrodes for providing a signal to said input electrode of said first transistor for equalizing the inequality in the voltages appearing at said output electrodes caused by said thermal energy;
and
means coupled to said feedback circuit for providing an output signal representative of the equalizing signal provided by said feedback circuit, said output signal being responsive to the temperature of said one of said first and second transistor means.

2 more elements

Dependencies are inferred from the claim text.

Low frequency electro-thermal filter

Life of this patent

Low frequency electro-thermal filter

Life of this patent

Abstract

Claims25