Method and apparatus for measuring an output signal of a floating transducer

• US 6,633,441 B1
• Filed: 07/12/2000
• Issued: 10/14/2003
• Est. Priority Date: 07/12/2000
• Status: Expired due to Term

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell International Limited (Marvell Technology Group Limited)
• Inventors: Lam, Steven C., Cheng, Yi
• Primary Examiner(s): HOLDER, REGINA NEAL
• Application Number:
  US09/615,062
• Time in Patent Office: 1,189 Days
• Field of Search: 360/67, 360/31, 360/46, 327/307, 327/560, 327/110
• US Class Current: 360/31
• CPC Class Codes: G11B 2005/001 Controlling recording characteristics of record carriers or transducing characteristics of transducers by means not being part of their structure
• CPC Class Codes: G11B 2005/0016 of magnetoresistive transducers
• CPC Class Codes: G11B 5/455 Arrangements for functional testing of heads; Measuring arrangements for heads
• CPC Class Codes: H03F 2203/45028 the differential amplifier amplifying transistors are folded cascode coupled transistors
• CPC Class Codes: H03F 2203/45676 the LC comprising one cascode current mirror
• CPC Class Codes: H03F 3/45192 Folded cascode stages

Abstract

A circuit for measuring signal output of a transducer includes an amplifier having a differential input and a single ended output referenced to a fixed potential. One transducer terminal is coupled through a source follower to an input terminal of the differential input and the other transducer terminal is coupled through a source follower and a resistive element to the other input terminal of the differential input whereby the transducer terminals are isolated from the fixed potential. A voltage to current converter converts the voltage at the single ended output to an output current that is applied to an input branch of a current mirror. A first output branch of the current mirror supplies a current equal to the converter output current to one terminal of the differential input. A second output branch of the current mirror supplies a current equal to the converter output current to the other terminal of the differential input. A third output branch of the current mirror supplies a multiple of the converter output current to a resistive element having a terminal connected to the fixed potential.

Claims

1. A circuit for measuring an output from a magnetic head comprising:

converting means having differential input means for converting a voltage to a current;

means for coupling the output from the magnetic head that is not referenced to a fixed potential to the differential input means; and

means responsive to the current from the converting means for producing a voltage for measurement referenced to a fixed potential.

2. A circuit for measuring an output from a magnetic head according to claim 1, wherein the converting means having the differential input means includes operational amplifier means and wherein the means for coupling the magnetic head output to the differential input means is substantially isolated from the fixed potential.

3. A circuit for measuring an output from a magnetic head according to claim 1, wherein the differential input means comprises first and second terminals and the coupling means comprises means isolated from the fixed potential for coupling a first terminal of the magnetic head to the differential input means first terminal and means isolated from the fixed potential for coupling a second terminal of the magnetic head to the differential input means second terminal.

4. A circuit for measuring an output from a magnetic head according to claim 3, wherein the means for coupling the first terminal of the magnetic head to the differential input means first terminal includes CMOS transistor means having a gate coupled to the first terminal of the magnetic head, a source coupled to the differential input first terminal and a drain coupled to the fixed potential and the means for coupling the second terminal of the magnetic head to the differential input means second terminal includes CMOS transistor means having a gate coupled to the second terminal of the magnetic head, a source coupled to the differential input means second terminal through resistive means and a drain coupled to the fixed potential.

5. A circuit for measuring an output from a magnetic head according to claim 4, further comprising means for feeding back the current from the converting means to the differential input means.

6. A circuit for measuring an output from a magnetic head according to claim 5, wherein the feed back means includes current mirror means comprising input branch means for receiving the current from the converting means, first output branch means coupled to the differential input means first terminal and second output branch means coupled to the differential input means second terminal.

7. A circuit for measuring an output from a magnetic head according to claim 6, wherein a current in the first output branch means of the current mirror means is substantially equal to the current from the converting means and the current in the second output branch means of the current mirror means is substantially equal to the current from the converting means.

8. A circuit for measuring an output from a magnetic head according to claim 7, wherein the current mirror means further comprises third output branch means for supplying a multiple of the current from the converting means to the voltage producing means.

9. A circuit for measuring an output from a magnetic head comprising:

a converter having a differential input for converting a voltage to a current;

a coupler for coupling the output from the magnetic head that is not referenced to a fixed potential to the differential input; and

a voltage forming device responsive to the current from the converter to produce a voltage for measurement referenced to a fixed potential.

10. A circuit for measuring an output from a magnetic head according to claim 9, wherein the converter having the differential input includes an operational amplifier and wherein the coupler for coupling the magnetic head output to the differential input is substantially isolated from the fixed potential.

11. A circuit for measuring an output from a magnetic head according to claim 9, wherein the differential input comprises first and second terminals and the coupler comprises a semiconductor device isolated from the fixed potential for coupling a first terminal of the magnetic head to the differential input first terminal and a semiconductor device isolated from the fixed potential for coupling a second terminal of the magnetic head to the second differential input terminal.

12. A circuit for measuring an output from a magnetic head according to claim 11, wherein the semiconductor device coupling the first terminal of the magnetic head to the differential input first terminal is a CMOS transistor having a gate coupled to the first terminal of the magnetic head, a source coupled to the differential input first terminal and a drain coupled to the fixed potential and the semiconductor device coupling the second terminal of the magnetic head to the differential input second terminal is a CMOS transistor having a gate coupled to the second terminal of the magnetic head, a source coupled to the differential input second terminal through a resistive element and a drain coupled to the fixed potential.

13. A circuit for measuring an output from a magnetic head according to claim 12, further comprising a feed back unit for feeding back the current from the converter to the differential input.

14. A circuit for measuring an output from a magnetic head according to claim 13, wherein the feed back unit includes a current mirror comprising an input branch for receiving the current from the converter, first output branch coupled to the differential input first terminal and a second output branch coupled to the differential input second terminal.

15. A circuit for measuring an output from a magnetic head according to claim 14, wherein a current in the first output branch of the current mirror is substantially equal to the current from the converter and the current in the second output branch of the current mirror is substantially equal to the current from the converter.

16. A circuit for measuring an output from a magnetic head according to claim 15, wherein the current mirror further comprises a third output branch for supplying a multiple of the current from the converter to the voltage forming device.

17. A method of measuring an output from a magnetic head in a circuit having a voltage to current converter with a differential input comprising the steps of:

coupling an output of the magnetic head that is not referenced to a fixed potential to the differential input of the converter that converts a voltage to a current; and

forming a voltage for measurement referenced to a fixed potential.

18. A method of measuring an output from a magnetic head according to claim 17, wherein the converter having the differential input includes an operational amplifier and wherein the coupling of the output of the magnetic head to the differential input is substantially isolated from the fixed potential.

19. A method of measuring an output from a magnetic head according to claim 18, wherein the differential input comprises first and second terminals, the coupling of the magnetic head output to the first terminal isolated from the fixed potential is through a semiconductor device and the coupling of the magnetic head output to the second terminal isolated from the fixed potential is through a semiconductor device.

20. A method of measuring an output from a magnetic head according to claim 19, wherein the semiconductor device coupling the first terminal of the magnetic head to the differential input first terminal is a CMOS transistor having a gate coupled to the first terminal of the magnetic head, a source coupled to the differential input first terminal and a drain coupled to the fixed potential and the semiconductor device for coupling the second terminal of the magnetic head to the differential input second terminal is a CMOS transistor having a gate coupled to the second terminal of the magnetic head, a source coupled to the differential input second terminal through a resistive element and a drain coupled to the fixed potential.

21. A method of measuring an output from a magnetic head according to claim 20, further comprising the step of feeding back the current from the converter to the differential input.

22. A method of measuring an output from a magnetic head according to claim 21, wherein the current from the converter is fed back through a current mirror in which an input branch receives the current from the converter, a first output branch supplies a current substantially equal to the current from the converter to the first differential input terminal and a second output branch supplies a current substantially equal to the current from the converter to the second differential input terminal.

23. A method of measuring an output from a magnetic head according to claim 22, wherein the current mirror further includes a third output branch that supplies a multiple of the current from the converter to form the voltage referenced to the fixed potential.

24. A transducer measuring circuit comprising:

an operational amplifier having a differential input and a single ended output;

coupling means for coupling a signal from the transducer that is not referenced to a fixed potential to the differential input;

converting means coupled to the amplifier output for converting a voltage at the single ended output to an output current; and

means for feeding back a signal from the converting means to the differential input,

wherein the single ended output is referenced to a fixed potential and the coupling means is substantially isolated from the fixed potential.

25. A transducer measuring circuit according to claim 24, wherein the feed back means includes a current mirror.

26. A transducer measuring circuit according to claim 25, wherein the differential input includes first and second input terminals, and wherein the signal from the transducer is coupled in series with a resistive element to the first and second terminals of the differential input, and the signal fed back by the current mirror means is applied to the first and second input terminals.

27. A transducer circuit according to claim 26, wherein the coupling of the transducer signal in series with the resistive element to the first and second terminals of the differential input includes:

a first CMOS transistor having a gate coupled to a first terminal of the transducer and a source connected to the first terminal of the differential input; and

a second CMOS transistor having a gate coupled a second terminal of the transducer and a source connected to one terminal of the resistive element, the other terminal of the resistive element being connected to the second terminal of the differential input,

the drains of the first and second CMOS transistors being connected to a reference potential.

28. A transducer circuit according to claim 27, wherein the current mirror means includes an input current branch coupled to the converting means, a first output current branch coupled to the first input terminal of the differential input and a second output current branch coupled to the second input terminal of the differential input.

29. A transducer circuit according to claim 28, wherein the current mirror means includes a third output current branch connected to one terminal of a resistive element having another terminal connected to the fixed potential.

30. A transducer circuit according to claim 29, wherein the first and second output current branches each supplies a current substantially equal to the output current from the converter means and the third output current branch supplies a multiple of the output current from the converting means to the resistive element having the terminal connected to the fixed potential.

31. A transducer circuit according to claim 30, wherein the transducer is a magneto-resistive head.

32. A magneto-resistive head voltage measuring circuit comprising:

a CMOS operational amplifier having a differential input stage coupled to a single ended output stage;

a CMOS coupler for coupling a voltage output from the magneto-resistive head that is not referenced to a fixed potential to the differential input stage;

a CMOS voltage to current converter coupled to the single ended amplifier output for converting a voltage at the single ended output to an output current; and

a CMOS feedback element for coupling a portion of the converter output current to the input of the differential input stage,

wherein the single ended output stage includes an output that is referenced to a fixed voltage line and the coupler for coupling the voltage from the magneto-resistive head to the differential input stage is isolated from the fixed voltage line.

33. A magneto-resistive head voltage measuring circuit according to claim 32, wherein the magneto-resistive head voltage coupler comprises:

a first source follower having a gate connected to a first terminal of the magneto-resistive head and a source connected to a first input of the differential stage;

a second source follower having a gate connected to a second terminal of the differential input stage and a source connected to one terminal of a resistive element, the other terminal of the resistive element being connected to a second input of the differential input stage, and

the drains of the first and second source followers being connected to a fixed potential line.

34. A magneto-resistive head measuring circuit according to claim 33, wherein the feedback element includes a current mirror.

35. A magneto-resistive head voltage measuring circuit according to claim 34, wherein the voltage to current converter comprises a CMOS transistor having a gate connected to the output of the single ended output stage, a source connected to the fixed voltage line and a drain connected to the current mirror.

36. A magneto-resistive head voltage measuring circuit according to claim 35, wherein the current mirror includes an input branch connected to the drain of the CMOS voltage to current converter transistor, a first output branch coupled to the first input of the differential input stage and a second output branch coupled to the second input of the differential input stage.

37. A magneto-resistive head voltage measuring circuit according to claim 36, wherein the first output branch couples a current substantially equal to the converter output current to the first input of the differential input stage and the second output branch couples a current substantially equal to the converter output current to the second input of the differential input stage.

38. A magneto-resistive head voltage measuring circuit according to claim 37, wherein the current mirror includes a third output branch for coupling a current corresponding to a multiple of the converter output current to one terminal of a resistive element having another terminal connected to the fixed voltage line.

39. A magneto-resistive head voltage measuring circuit according to claim 34, wherein the current mirror is a CMOS current mirror.

40. In a magneto-resistive head measuring circuit including an operational amplifier having a differential input and a single ended output referenced to a fixed potential, a method of measuring an output voltage of the magneto-resistive head comprising the steps of:

coupling the output voltage of the magneto-resistive head that is not referenced to a fixed potential to the differential input;

converting an output voltage of the single ended stage to an output current; and

feeding back the output current to the differential input,

wherein the coupling of the magneto-resistive head output voltage is isolated from the fixed potential.

41. In a magneto-resistive head measuring circuit including an operational amplifier having a differential input and a single ended output returned to a fixed reference potential, a method of measuring an output voltage of the magneto-resistive head according to claim 40, wherein the output current is fed back through a current mirror.

42. In a magneto-resistive head measuring circuit including an operational amplifier having a differential input and a single ended output returned to a fixed reference potential, a method of measuring an output voltage of the magneto-resistive head according to claim 41, wherein the output voltage of the magneto-resistive head is coupled to a first terminal of the differential input through a first source follower having its gate coupled to one terminal of the magneto-resistive head, its source connected to the differential input first terminal and its drain connected to a fixed voltage and to a second terminal of the differential input through a second source follower having its gate coupled to another terminal of the magneto-resistive head, its source connected to the differential amplifier second terminal through a resistive element and its drain connected to the fixed voltage.

43. In a magneto-resistive head measuring circuit including an operational amplifier having a differential input and a single ended output returned to a fixed reference potential, a method of measuring an output voltage of the magneto-resistive head according to claim 42, wherein the output.current is received by an input branch of the current mirror, a first output branch of the current mirror supplies a current substantially equal to the output current to the first input terminal of the differential input and a second output branch of the current mirror supplies a current substantially equal to the output current to the second terminal of the differential input.

44. In a magneto-resistive head measuring circuit including an operational amplifier having a differential input and a single ended output returned to a fixed reference potential, a method of measuring an output voltage of the magneto-resistive head according to claim 43, wherein a third output branch of the current mirror supplies a multiple of the output current to a resistive element that is returned to the fixed potential.