Voltage Buffer for Input Voltages Above a Supply Voltage or Below Ground Voltage

• US 20200067467A1
• Filed: 08/24/2018
• Published: 02/27/2020
• Est. Priority Date: 08/24/2018
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Choe, Soo-Chang, Petrie, Craig S.
• Granted Patent: US 10,644,659 B2
• Time in Patent Office: Days
• CPC Class Codes: G01R 19/2513 Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging
• CPC Class Codes: G01R 21/133 by using digital technique
• CPC Class Codes: H03F 2200/151 A source follower being used in a feedback circuit of an amplifier stage
• CPC Class Codes: H03F 2200/219 Follower transistors are added at the input of the amplifier, e.g. source or emitter followers
• CPC Class Codes: H03F 2200/69 the amplifier stage being a common drain coupled MOSFET, i.e. source follower
• CPC Class Codes: H03F 2203/45006 the addition of two signals being made by two emitter or source coupled followers
• CPC Class Codes: H03F 2203/45144 At least one follower being added at the input of a dif amp
• CPC Class Codes: H03F 2203/45522 the FBC comprising one or more potentiometers
• CPC Class Codes: H03F 2203/45562 the IC comprising a cross coupling circuit, e.g. comprising two cross-coupled transistors
• CPC Class Codes: H03F 2203/45591 the IC comprising one or more potentiometers
• CPC Class Codes: H03F 2203/45612 the IC comprising one or more input source followers as input stages in the IC
• CPC Class Codes: H03F 3/16 with field-effect devices
• CPC Class Codes: H03F 3/393 with field-effect devices
• CPC Class Codes: H03F 3/45183 Long tailed pairs H03F3/4521, H03F3/45237 take precedence
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit
• CPC Class Codes: H03F 3/50 Amplifiers in which input is applied to, or output is derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower

Abstract

A buffer amplifier comprises a source follower and a feedback amplifier. The feedback amplifier may be configured to control a drain current of the source follower to remain substantially constant independent of a load.

Claims

1. Apparatus, comprising:

a buffer amplifier comprising a source follower and a feedback amplifier, the feedback amplifier configured to control a drain current of the source follower to remain substantially constant independent of a load, wherein the buffer amplifier is coupled to an input voltage based upon a line voltage and to a supply voltage derived from the input voltage.

2. The apparatus of claim 1, wherein the buffer amplifier presents an output impedance based upon the feedback amplifier.

3. The apparatus of claim 1, wherein the buffer amplifier further comprises a plurality of MOSFETs, wherein at least one of the plurality of MOSFETs is coupled to the source follower and wherein the feedback amplifier is configured to control the drain current of the source follower to match a drain current of at least one of the plurality of MOSFETs.

4. The apparatus of claim 1, wherein the feedback amplifier is further configured to control a voltage of a drain of the source follower.

5. The apparatus of claim 4, wherein the controlled voltage of the drain of the source follower is within approximately 300 mV of a supply voltage.

7. The apparatus of claim 1, wherein a common mode voltage associated with the input voltage is greater than the supply voltage.

8. The apparatus of claim 1, wherein a common mode voltage associated with the input voltage is within approximately 300 mV of the supply voltage.

9. The apparatus of claim 1, further comprising an attenuator coupled to an input of the buffer amplifier, wherein the attenuator comprises at least one resistor.

10. The apparatus of claim 9, wherein an input impedance presented by the buffer amplifier is effectively 1000 times greater than an output impedance presented by the attenuator.

11. The apparatus of claim 1, wherein an output of the source follower of the buffer amplifier is coupled to a variable gain amplifier.

12. The apparatus of claim 11, wherein an impedance presented by an input of the variable gain amplifier is effectively 1000 times greater than an output impedance presented by the buffer amplifier.

13. The apparatus of claim 1, wherein the buffer amplifier is realized in an integrated circuit.

14. The apparatus of claim 1, wherein the feedback amplifier comprises a MOSFET coupled to a source of the source follower of the buffer amplifier and wherein the MOSFET is configured to control the drain current of the source follower.

15. The apparatus of claim 14, further comprising a capacitor coupled between the drain of the source follower and a gate of the MOSFET, wherein the capacitor is configured to control a frequency response of the buffer amplifier.

16. The apparatus of claim 1, wherein the feedback amplifier comprises at least two source followers.

17. The apparatus of claim 16, wherein a gate of a first source follower of the feedback amplifier is coupled to a reference voltage, and a gate of a second source follower of the feedback amplifier is coupled to a drain voltage of the source follower of the buffer amplifier.

18. The apparatus of claim 17, wherein the drain voltage is within approximately 100 mV of the reference voltage.

19. The apparatus of claim 16, wherein the first and second source followers of the feedback amplifier are coupled to a differential amplifier.

20. The apparatus of claim 19, wherein the first and second source followers of the feedback amplifier are configured to shift at least one voltage of a differential pair at an input of the differential amplifier so that a voltage of the differential pair is in an operating region of the differential amplifier.

6. (canceled)

21. A power monitoring circuit to monitor a line voltage associated with a power source, comprising:

a buffer amplifier comprising a source follower and a feedback amplifier, the feedback amplifier configured to control a drain current of the source follower to remain substantially constant independent of a load.

22. The power monitoring circuit of claim 21, wherein the buffer amplifier is coupled to an input voltage derived from a line voltage and to a supply voltage derived from the line voltage.

23. The power monitoring circuit of claim 22, wherein a common mode voltage associated with the input voltage is greater than the supply voltage.

24. The power monitoring circuit of claim 22, wherein a common mode voltage associated with the input voltage is within approximately 300 mV of the supply voltage.

25. The power monitoring circuit of claim 21, wherein the supply voltage is an AC voltage.

26. The power monitoring circuit of claim 21, wherein the supply voltage is a DC voltage.

27. The power monitoring circuit of claim 21, wherein an input impedance presented by the buffer amplifier is effectively greater than 100 MOhms.

28. The power monitoring circuit of claim 21, wherein an output impedance presented by the buffer amplifier is effectively less than 100Ω

.

29. The power monitoring circuit of claim 21, further comprising a variable gain amplifier coupled to an output of the buffer amplifier.

30. The power monitoring circuit of claim 29, wherein an output of the variable gain amplifier is coupled to an analog-to-digital converter.

31. The power monitoring circuit of claim 30, wherein the analog-to-digital converter comprises a sigma-delta modulator.

32. The power monitoring circuit of claim 30, wherein an output of the analog-to-digital converter is coupled to a digital signal processor.

33. The power monitoring circuit of claim 21, further comprising a chopper circuit coupled to an input of the buffer amplifier.

34. The power monitoring circuit of claim 21, wherein the power monitoring circuit is realized in an integrated circuit.

35. Apparatus comprising:

means for controlling a drain current of a source follower in a buffer amplifier to remain substantially constant independent of a load; and

means for controlling an output impedance of the buffer amplifier.

36. The apparatus of claim 35, further comprising:

means for controlling the drain current of the source follower to match a drain current of at least one of a plurality of MOSFETs in the buffer amplifier.

37. The apparatus of claim 35, further comprising:

means for controlling a voltage at a drain of the source follower.

38. The apparatus of claim 35, further comprising:

means for shifting an output voltage of the buffer amplifier.

39. The apparatus of claim 35, further comprising:

means for controlling a capacitance of the source follower.