Sensors and sensor circuits which convert sense currents to digital values
A sensor circuit, e.g., a circuit for use with a sensor that develops a current responsive to temperature, includes a digital to analog (D/A) comparison circuit having an analog sense current input and a digital input, the D/A comparison circuit operative to compare a digital value at the digital input to a sense current at the sense current input and to responsively generate a comparison signal. The sensor circuit further includes a control circuit configured to provide digital values to the digital input of the D/A comparison circuit responsive to the comparison signal and to generate a digital output corresponding to the sense current.
1. A sensor circuit comprising:
a digital to analog (D/A) comparison circuit comprising an analog sense current input, a digital input and a plurality of series-coupled resistors throuah which an analog sense current at the analog sense current input passes, the D/A comparison circuit configured to generate first and second voltages responsive to respective nodes of the plurality of series-coupled resistors, to scale the second voltage responsive to a digital value at the digital input and to compare the scaled second voltage to the first voltage to generate a comparison signal; and
a control circuit configured to provide digital values to the digital input of the D/A comparison circuit responsive to the comparison signal and to generate a digital output corresponding to the sense current.
2. A circuit according to claim 1 , wherein the D/A comparison circuit comprises:
a voltage generator circuit that generates a reference voltage and a variable voltage responsive to the sense current;
a scaling circuit that scales the variable voltage responsive to the digital value; and
a voltage comparator that generates the comparison signal responsive to a comparison of the scaled variable voltage and the reference voltage.
3. A circuit according to claim 2 , wherein the scaling circuit comprises:
a plurality of resistors coupled in series between a node that develops the variable voltage and a signal ground node; and
a plurality of switches, respective ones of which are configured to bypass respective ones of the plurality of resistors responsive to respective bits of the digital value at the digital input.
4. A circuit according to claim 2 , wherein the voltage generator circuit comprises a bandgap reference circuit.
5. A circuit according to claim 2 , wherein the D/A comparison circuit has a reference adjustment input, and wherein the voltage generator circuit is operative to adjust the reference voltage responsive to a digital value at the reference adjustment input.
6. A circuit according to claim 5 , wherein the voltage generator circuit comprises:
a plurality of resistors coupled in series between a node that develops the reference voltage and a signal ground node; and
a plurality of switches, respective ones of which are configured to bypass respective ones of the plurality of resistors responsive to respective bits of the digital value at the reference adjustment input.
7. A circuit according to claim 2 , wherein the voltage generator circuit comprises:
a first resistor connected between the sense current input and a node at which the variable voltage is developed;
a second resistor connected between the node at which the variable voltage is developed and a node at which the reference voltage is developed;
a bipolar transistor having its base terminal coupled to its collector terminal and a signal ground node; and
a third resistor connected between an emitter terminal of the bipolar transistor and the node at which the reference voltage is developed.
8. A circuit according to claim 7 , wherein the third resistor comprises a plurality of resistors connected in series between the emitter terminal of the bipolar transistor and the node at which the variable voltage is developed, and wherein the voltage generator circuit further comprises a plurality of switches, respective ones of which are coupled in parallel with respective ones of the plurality of resistors.
9. A circuit according to claim 2 , wherein the voltage generator circuit comprises:
a first resistor connected between the sense current input and a node at which the variable voltage is developed;
a second resistor connected between the node at which the variable voltage is developed and a node at which the reference voltage is developed;
a field effect transistor having its gate terminal coupled to its drain terminal and a signal ground node; and
a third resistor connected between a source terminal of the field effect transistor and the node at which the reference voltage is developed.
10. A circuit according to claim 9 , wherein the third resistor comprises a plurality of resistors connected in series between the source terminal of the field effect transistor and the node at which the variable voltage is developed, and wherein the voltage generator circuit further comprises a plurality of switches, respective ones of which are coupled in parallel with respective ones of the plurality of resistors.
11. A circuit according to claim 1 , wherein the D/A comparison circuit comprises:
a voltage generator circuit that generates a reference voltage and a variable voltage responsive to the sense current;
a scaling circuit that scales the reference voltage responsive to the digital value; and
a voltage comparator that generates the comparison signal responsive to a comparison of the variable voltage and the scaled reference voltage.
12. A circuit according to claim 11 , wherein the scaling circuit comprises:
a plurality of resistors coupled in series between a node that develops the reference voltage and a signal ground node; and
a plurality of switches, respective ones of which are configured to bypass respective ones of the plurality of resistors responsive to respective bits of the digital value at the digital input.
13. A circuit according to claim 11 , wherein the voltage generator circuit comprises a bandgap reference circuit.
14. A circuit according to claim 11 , wherein the D/A comparison circuit has a reference adjustment input, and wherein the voltage generator circuit is operative to adjust the reference voltage responsive to a digital value at the reference adjustment input.
15. A circuit according to claim 14 , wherein the voltage generator circuit comprises:
a plurality of resistors coupled in series between a node that develops the reference voltage and a signal ground node; and
a plurality of switches, respective ones of which are configured to bypass respective ones of the plurality of resistors responsive to respective bits of the digital value at the reference adjustment input.
16. A circuit according to claim 11 , wherein the voltage generator circuit comprises:
a first resistor connected between the sense current input and a node at which the reference voltage is developed;
a second resistor connected between the node at which the reference voltage is developed and a node at which the variable voltage is developed; and
a bipolar transistor having its base terminal coupled to its collector terminal and a signal ground node and its emitter terminal coupled to the node at which the variable voltage is developed.
17. A circuit according to claim 16 , wherein the second resistor comprises a plurality of resistors connected in series between the emitter terminal of the bipolar transistor and the node at which the reference voltage is developed, and wherein the voltage generator circuit further comprises a plurality of switches, respective ones of which are coupled in parallel with respective ones of the plurality of resistors.
18. A circuit according to claim 11 , wherein the voltage generator circuit comprises:
a first resistor connected between the sense current input and a node at which the reference voltage is developed;
a second resistor connected between the node at which the reference voltage is developed and a node at which the variable voltage is developed; and
a field effect transistor having its gate terminal coupled to its drain terminal and a signal ground node and its source terminal coupled to the node at which the variable voltage is developed.
19. A circuit according to claim 18 , wherein the second resistor comprises a plurality of resistors connected in series between the source terminal of the field effect transistor and the node at which the reference voltage is developed, and wherein the voltage generator circuit further comprises a plurality of switches, respective ones of which are coupled in parallel with respective ones of the plurality of resistor.
20. A circuit according to claim 1 , further comprising an adjustment circuit operative to control the first voltage and/or the second voltage.
21. A temperature sensor comprising:
a digital to analog (D/A) comparison circuit comprising an analog sense current input, a digital input and a plurality of series-coupled resistors through which an analog sense current at the analog sense current input passes, the D/A comparison circuit configured to generate first and second voltages responsive to respective nodes of the plurality of series-coupled resistors, to scale the second voltage responsive to a digital value at the digital input and to compare the scaled second voltage to the first voltage to generate a comparison signal;
a control circuit configured to provide digital values to the digital input of the D/A comparison circuit responsive to the comparison signal and to generate a digital output corresponding to the sense current; and
a temperature transducer operative to generate a current at the analog current sense input responsive to temperature.
22. A sensor according to claim 21 , wherein the D/A comparison circuit comprises:
a voltage generator circuit that generates a reference voltage and a variable voltage responsive to the sense current;
a scaling circuit that scales a first one of the variable voltage and the reference voltage responsive to the digital value; and
a voltage comparator that generates the comparison signal responsive to a comparison of the scaled first one of the variable voltage and the reference voltage to a second one of the variable voltage and the reference voltage.
23. A sensor according to claim 22 , further comprising an adjustment circuit operative to adjust the reference voltage.
24. A sensor according to claim 21 , wherein the D/A comparison circuit and the control circuit are included in an integrated circuit.
25. A liquid crystal display (LCD) driving integrated circuit (IC) comprising:
a digital to analog (D/A) comparison circuit comprising an analog sense current input, a digital input and a plurality of series-coupled resistors through which an analog sense current at the analog sense current input passes, the D/A comparison circuit configured to generate first and second voltages responsive to respective nodes of the plurality of series-coupled resistors, to scale the second voltage responsive to a digital value at the digital input and to compare the scaled second voltage to the first voltage to generate a comparison signal;
a control circuit configured to provide digital values to the digital input of the D/A comparison circuit responsive to the comparison signal and to generate a digital output corresponding to the sense current; and
an LCD driving circuit operative to drive an LCD responsive to the generated digital output.
26. An LCD driving IC according to claim 25 , wherein the D/A comparison circuit comprises:
a voltage generator circuit that generates a reference voltage and a variable voltage responsive to the sense current;
a scaling circuit that scales a first one of the variable voltage and the reference voltage responsive to the digital value; and
a voltage comparator that generates the comparison signal responsive to a comparison of the scaled first one of the variable voltage and the reference voltage to a second one of the variable voltage and the reference voltage.
27. An LCD driving IC according to claim 25 , further comprising an adjustment circuit operative to adjust the first voltage and/or the second voltage.
28. An LCD driving IC according to claim 25 , wherein the sense current represents temperature.