Thermal power sensor

An apparatus for generating an output signal indicative of the magnitude of an input signal, said apparatus comprising:

• first and second matched circuit devices thermally isolated from each other and substantially isolated from ambient energy, each of said circuit devices having a variable characteristic controlled by the amount of thermal energy incident thereon;
• means for coupling the first circuit device to said input signal so that thermal energy derived from said input signal is incident on said first circuit device, thereby controlling the variable characteristics of said first circuit device;
• means for sensing the variable characteristics of said first and second circuit devices and for generating first and second control signals corresponding thereto;
• means linearly responsive to said first and second control signals for applying additional thermal energy differentially to said first and second circuit devices over a first range of said input signal to raise the thermal energy of said first and second circuit devices toward a quiescent, thermally balanced condition that is greater than that due to ambient thermal energy, the magnitude of said additional differential thermal energy being linearly related to the magnitude of said input signal over said first range;
• a source of thermal energy responsive to at least one of said first and second control signals in accordance with a predetermined relationship for applying further additional thermal energy to said second circuit device over a second range of said input signal, the magnitude of said further additional thermal energy having said predetermined relationship to the magnitude of said input signal over said second range;
• and
• means for generating said output signal as a function of the magnitude of said additional thermal energy and said further additional thermal energy.

In a voltage and power sensing device including a pair of matched, forward-biased bipolar transistors connected in a differential common emitter configuration, wherein each transistor is associated with one of a pair of matched resistors, heat transfer means thermally coupling each resistor to a respective transistor so that heat generated in the resistors is coupled to their respective transistors to cause temperature variations therein, said transistors exhibiting a collector-emitter current that is a function of the temperature of the transistor, whereby the collector-emitter current through said transistors varies as a result of the power being dissipated by the respective resistor, said transistors being connected to a first amplifier which senses and amplifies a differential voltage resulting from different currents flowing through said transistors and produces an output signal in response thereto, the output signal being connected in a feedback loop to the second of the matched resistors, the first matched resistor being connected to an input terminal for receiving a signal or power source to be sensed, the improvement comprising:

• a respective cascode transistor connected in series with each matched transistor, said cascode transistors having their respective bases coupled to differential outputs of a first differential amplifier in an attempt to balance the temperatures of said matched transistors by varying bias power dissipated in said matched transistors as a function of the differential outputs of said first differential amplifier, a voltage drop across said matched transistors varying as a linear function of the power being sensed;
• and
• means connected to the output of said first differential amplifier providing an indication of the said power being sensed, said indication bearing a substantially linear relationship to said differential voltage.

A voltage and power sensor for determining the voltage or power from an external source, said sensor comprising:

• first and second matched sense transistors thermally isolated from each other and substantially isolated from ambient thermal energy, said sense transistors having their bases coupled to each other and to a fixed voltage and their emitters connected to each other and to a current source;
• a first thermal element thermally coupled to said first sense transistor, said first thermal element dissipating power, said first thermal element being coupled to said external source so that the current through said first sense transistor varies as a function of the heat coupled to said first transistor by power dissipated in said first thermal element;
• a differential amplifier generating a differential output that is proportional to the difference in currents through said first and second sense transistors;
• first and second heating transistors thermally coupled to said first and second sense transistors, respectively, said first and second heating transistors having respective emitters connected to collectors of respective sense transistors and respective bases connected to each other and to a higher fixed voltage so that the collector-emitter voltages of said sense transistors remain substantially constant;
• and
• first and second cascode transistors having respective bases connected to respective outputs of said differential amplifier and respective emitters connected to collectors of respective heating transistors, said cascode transistors varying the collector-emitter voltages of respective heating transistors causing a change in the power dissipated in the heating transistors which results in a temperature change of the heating transistors as a linear function of the output from said differential amplifier, thereby attempting to thermally balance said sense transistors, whereby the output of said differential amplifier is indicative of the power from said external source.

A voltage and power sensor for determining the power from an external source, said sensor comprising:

• first and second semiconductor means thermally isolated from each other and substantially isolated from ambient thermal energy, each of said semiconductor means generating an electrical output that is a function of the temperature of said semiconductor means, said first and second semiconductor means dissipating power as a linear function of respective first and second control signals applied to said first and second semiconductor means, respectively;
• a first thermal element thermally coupled to said first semiconductor means, said thermal element dissipating power as a function of the square of a voltage across said thermal element, said first thermal element being coupled to said external source so that the current through said first semiconductor means varies as a function of the heat coupled to said first semiconductor means by power dissipated in said first thermal element;
• and
• a differential amplifier generating said first and second control signals as a function of the difference in electrical outputs from said first and second semiconductor means, thereby varying the power dissipated in said first and second semiconductor means as a linear function of the output from said differential amplifier in an attempt to thermally balance the temperatures of said first and second semiconductor means, whereby the output of said differential amplifier is indicative of the power from said external source.