Low temperature error thermal sensor
View Patent ↗A thermal sensor in some embodiments comprises two temperature-sensitive branches, each including a thermal-sensing device, such as one or more bipolar-junction transistors, and a current source for generating a current density in the thermal-sensing device to generate a temperature-dependent signal. The thermal sensor further includes a signal processor configured to multiply the temperature-dependent signal from the branches by respective and different gain factors, and combine the resultant signals to generate an output signal that is substantially proportional to the absolute temperature the thermal sensor is disposed at.
1 . A thermal sensor, comprising:
a temperature-sensitive device comprising a bandgap thermal-sensing device;
a first current source adapted to generate a current of a first value;
a second current source adapted to generate a current of a second value different from the first value;
a first switching device (SW1) adapted to pass the current generated by the first current source through the bandgap thermal-sensing device;
a second switching device (SW2) adapted to pass the current generated by the second current source through the bandgap thermal-sensing device;
the bandgap thermal-sensing device being adapted to generate a first and a second output signals responsive to temperature and the current of the first and second values, respectively;
a third switching device (SW3);
a gain circuit operatively connectable in parallel to the bandgap thermal-sensing device through the third switch and adapted to adjust the first or second output signal when connected to the bandgap thermal-sensing device; and
a signal processing circuit operatively connected to receive the first and second output signals, and to generate an output signal based on the first and second output signals.
2 . The thermal sensor of claim 1 , wherein one of the first and second output signals is a signal generated by the bandgap thermal-sensing device while being connected to the gain circuit, wherein the output signal of the signal processing circuit is a linear combination between the first and second signals.
3 . The thermal sensor of claim 2 , wherein the output signal of the signal processing circuit is a differential signal between the first and second signals.
4 . The thermal sensor of claim 1 , wherein the first, second, and third switching devices are adapted to be actuated cooperatively to alternately connect the first and current sources to the bandgap thermal-sensing device, and connect the gain circuit to the bandgap thermal-sensing device when one of the first and second current sources is connected to the bandgap thermal-sensing device and disconnect the gain circuit from the bandgap thermal-sensing device when the other one of the first and second current sources is connected to the bandgap thermal-sensing device.
5 . The thermal sensor of claim 4 , wherein the bandgap thermal-sensing device is adapted to generate a voltage dependent on a combination of a state of connection between the bandgap thermal-sensing device with the first and second current sources and with the gain circuit.
6 . The thermal sensor of claim 5 , wherein the bandgap thermal-sensing device comprises a bipolar-junction transistor having a gate, an emitter and a collector, wherein the voltage generated by the bandgap thermal-sensing device is base-to-emitter voltage (V BE ).
7 . The thermal sensor of claim 6 , wherein the output of the signal processing circuit is indicative of a differential voltage, dV BE , given by one of the expressions for dV BE in the following table:
SW1
SW2
SW3
V BE
dV BE
On
Off
On
V BE3
V BE3 − V BE2
Off
On
Off
V BE2
On
Off
Off
V BE1
V BE4 − V BE1 .
Off
On
On
V BE4
8 . The thermal sensor of claim 6 , wherein the first and second current sources and bipolar-junction transistor are configured to generate a current density in the bipolar-junction transistor, and wherein the current densities are different for the first and second current sources.
9 . The thermal sensor of claim 1 , wherein the signal processing circuit comprises an analog-to-digital converter (ADC) adapted to receive the output signals from the bandgap thermal-sensing device.
10 . The thermal sensor of claim 1 , wherein the output signal generated by the signal processing circuit is substantially proportional to absolute temperature at the thermal sensor in a temperature range from −50° C. to 150° C.
11 . The thermal sensor of claim 10 , wherein each temperature corresponding to the output signal generated by the signal processing circuit within the temperature range differs by no more than 5° C. from a temperature determined by proportional relationship between absolute temperature and output signal generated by the signal processing circuit.
12 . The thermal sensor of claim 1 , wherein, the bandgap thermal-sensing devices comprises a field-effect transistor, wherein the first and second current sources and field-effect transistor are configured to generate a current density in the field-effect transistor, and wherein the current densities are different for the first and second current sources.