Production-test die temperature measurement method and apparatus
View Patent ↗A die temperature measurement system ( 300 ) includes an external test environment setup ( 352 ) and an integrated circuit ( 302 ). The external test environment setup ( 352 ) includes means to force and accurately measure electrical variables. The integrated circuit ( 302 ) includes a bipolar transistor ( 325 ); a selectable switch ( 340 ) for selecting from plurality of integrated resistances ( 342, 344 ) to be coupled in series between a base ( 322 ) of the bipolar transistor and a first input ( 362 ); and a selectable-gain current mirror ( 310 ) with a gain, a programmable current-mirror output coupled to the collector ( 326 ) of the bipolar transistor. The bipolar transistor and optional diodes ( 335 ) are sequentially biased with a set of proportional collector current levels. For each bias condition, the temperature-dependent voltage produced by the structure is extracted and stored. Die temperature is obtained through algebraic manipulation ( 450 ) of this data. Parasitic resistance and I/O pad leakage effects are canceled.
1. A method to measure temperature in a temperature sensing circuit, the method comprising:
1) coupling together the temperature sensing circuit including at least one bipolar transistor and a current mirror with a gain, and a programmable current-mirror output coupled to a collector of the bipolar transistor;
2) setting the gain of the current mirror to a first value from a set of current gain values;
3) measuring an output signal produced by the temperature sensing circuit by
a) setting a voltage magnitude of an input voltage between a first I/O pad and a third I/O pad of the temperature sensing circuit,
b) changing a switchable-resistance between at least a first resistance value and a second resistance value, the switchable-resistance disposed between the first I/O pad of the temperature sensing circuit and a base of the bipolar transistor,
c) measuring, between the first I/O pad and a second I/O pad of the temperature sensing circuit, the output signal in response to the input voltage, and
increasing the voltage magnitude of the input voltage, and repeating steps a through c, in response to the output signal being measured with the second resistance applied being greater than the output signal being measured with the first resistance applied, decreasing the voltage magnitude of the input voltage, and repeating steps a through c, in response to the output signal being measured with the second resistance applied being less than the output signal being measured with the first resistance applied;
repeating steps 2 through 3 until at least each of the current gain values has been used to set the gain of the current mirror and the output signal measured; and
4) calculating a temperature produced by the temperature sensing circuit by using each output signal that has been measured for each of the set of current gain values used to set the gain of the current mirror.
2. The method of claim 1 , wherein the increasing the voltage magnitude of the input voltage includes decreasing a maximum voltage down to a last value tested of the input voltage and repeating steps a through c.
3. The method of claim 2 , wherein the magnitude of the maximum voltage is up to the magnitude of a positive supply voltage.
4. The method of claim 1 , wherein the coupling together a temperature sensing circuit includes at least one additional bipolar transistor coupled in series between an emitter of the bipolar transistor and the second I/O pad.
5. The method of claim 4 , wherein the at least one additional bipolar transistor is coupled to form a diode.
6. The method of claim 4 , wherein the calculating a temperature produced by the temperature sensing circuit by using each output signal that has been measured includes calculating the temperature T in kelvin by
T
=
1
k
q
ln
(
I
C
1
I
C
2
)
×
⌊
2
·
(
V
MEAS
(
Ngs
=
N
)
-
V
MEAS
(
Ngs
=
1
)
)
-
(
V
MEAS
(
Ngs
=
2
N
)
-
V
MEAS
(
Ngs
=
2
)
)
⌋
1
+
Number_of
_Additional
_Cascaded
_BJTs
where V MEAS(Ngs=N) is a measured voltage between first I/O pad and second I/O pad to an integrated circuit with a current gain N gs through which one collector current is selected from the set of current gain values I, 2I, NI and 2NI provided by the current mirror, k is a Boltzmann's constant, q is an electron charge, ln is a natural logarithm function, I is a collector current at a first time interval, 2I is a collector current at a second time interval, NI is a collector current at a third time interval, and 2NI is a collector current at a fourth time interval and Number_of_Additional_Cascaded_BJTs is an integer number of the additional bipolar transistors.
7. The method of claim 1 , further comprising:
increasing a minimum voltage up to a last value tested of the input voltage, and repeating steps a through c, in response to the output signal being measured with the second resistance applied being greater than the output signal being measured with the first resistance applied.
8. The method of claim 7 , wherein the magnitude of the minimum voltage is down to a ground voltage.
9. The method of claim 8 , wherein a negative supply voltage is set to a ground potential.
10. The method of claim 1 , wherein the coupling together a temperature sensing circuit includes at least one driver with an input coupled to a collector of the bipolar transistor and an output coupled to a base of the bipolar transistor.
11. The method of claim 10 , wherein the coupling together a temperature sensing circuit includes at least one additional bipolar transistor coupled in series between an emitter of the bipolar transistor and the second I/O pad.
12. The method of claim 11 , wherein the at least one additional bipolar transistor is coupled to form a diode.