Current sensor comprising differential amplifier biased by leakage current
View Patent ↗A current sensor is disclosed comprising a differential amplifier including a first node, a second node, and an output. The current sensor further comprises a first resistor having a first end coupled to the first node and a second end for coupling to a transducer, and a second resistor having a first end coupled to the second node and a second end. When the second end of the second resistor is unconnected and the differential amplifier is driven with a supply voltage, the first node is biased by a first leakage current and the second node is biased by a second leakage current such that the output represents a current flowing through the transducer.
1. A current sensor comprising:
a differential amplifier comprising a first node, a second node, and an output;
a first resistor having a first end coupled to the first node and a second end for coupling to a transducer; and
a second resistor having a first end coupled to the second node and a second end,
wherein when the second end of the second resistor is unconnected and the differential amplifier is driven with a supply voltage, the first node is biased by a first leakage current and the second node is biased by a second leakage current such that the output represents a current flowing through the transducer.
2. The current sensor as recited in claim 1 , wherein the first leakage current substantially matches the second leakage current.
3. The current sensor as recited in claim 1 , wherein the output represents a fraction of the first leakage current.
4. The current sensor as recited in claim 1 , wherein:
the first resistor comprises a semiconductor resistor; and
the second resistor comprises a semiconductor resistor.
5. The current sensor as recited in claim 4 , wherein when a bias voltage is applied to the transducer, the bias voltage is applied to an isolation well of the first resistor and the bias voltage is applied to an isolation well of the second resistor.
6. The current sensor as recited in claim 5 , wherein:
a body of the first resistor and the isolation well form a first diode operable to provide protection against electrostatic discharge (ESD); and
a body of the second resistor and the isolation well form a second diode operable to provide protection against ESD.
7. The current sensor as recited in claim 6 , wherein each of the first and second resistor comprise:
a first ESD resistor comprising a first polarity diode operable to protect against a positive ESD; and
a second ESD resistor comprising a second polarity diode operable to protect against a negative ESD.
8. The current sensor as recited in claim 7 , wherein:
the first ESD resistor comprises a P-type semiconductor; and
the second ESD resistor comprises a N-type semiconductor.
9. The current sensor as recited in claim 1 , wherein the differential amplifier comprises:
a first field effect transistor (FET) comprising a first gate connected to the first node; and
a second FET comprising a second gate connected to the second node.
10. The current sensor as recited in claim 9 , wherein when a bias voltage is applied to the transducer, the bias voltage is applied to a source of the first FET and the bias voltage is applied to a source of the second FET.
11. The current sensor as recited in claim 10 , wherein when the bias voltage is applied to the transducer, the bias voltage is applied to an isolation well of the first FET and the bias voltage is applied to an isolation well of the second FET.
12. The current sensor as recited in claim 1 , wherein the current sensor is incorporated in a disk drive comprising:
a disk;
a head actuated over the disk; and
a fly height transducer operable to generate a fly height signal for the head; wherein the current sensor is operable to detect a current flowing through the fly height transducer.
13. The current sensor as recited in claim 12 , wherein the fly height transducer comprises a tunneling sensor.
14. A method of sensing current using a differential amplifier, the differential amplifier comprising a first node, a second node, and an output, the method comprising:
coupling a first end of a first resistor to the first node and a second end of the first resistor to a transducer;
coupling a first end of a second resistor to the second node and leaving a second end of the second resistor unconnected; and
biasing the first node with a first leakage current and biasing the second node with a second leakage current such that the output represents a current flowing through the transducer.
15. The method as recited in claim 14 , wherein the first leakage current substantially matches the second leakage current.
16. The method as recited in claim 14 , wherein the output represents a fraction of the first leakage current.
17. The method as recited in claim 14 , wherein the first resistor comprises a semiconductor resistor and the second resistor comprises a semiconductor resistor, the method further comprising:
applying a bias voltage to the transducer;
applying the bias voltage to an isolation well of the first resistor; and
applying the bias voltage to an isolation well of the second resistor.
18. The method as recited in claim 14 , wherein the differential amplifier comprises:
a first field effect transistor (FET) comprising a first gate connected to the first node; and
a second FET comprising a second gate connected to the second node,
the method further comprising:
applying a bias voltage to the transducer;
applying the bias voltage to a source of the first FET; and
applying the bias voltage to a source of the second FET.
19. The method as recited in claim 18 , further comprising:
applying the bias voltage to an isolation well of the first FET; and
applying the bias voltage to an isolation well of the second FET.
20. The method as recited in claim 14 , wherein the differential amplifier is operable to sense a current flowing through a fly height transducer of a disk drive.
21. The method as recited in claim 20 , wherein the fly height transducer comprises a tunneling sensor.