Linear regulator with temperature compensated bias current

Abstract

A solid-state circuit is presented which may comprise a pass device, a control circuit, and a leakage current compensation circuit. The pass device may have a first terminal, a second terminal and a drive terminal, wherein the first terminal of the pass device is coupled with an input terminal of the solid-state circuit, and wherein the second terminal of the pass device is coupled with an output terminal of the solid-state circuit. The control circuit may be coupled with the drive terminal of the pass device and may be configured to drive the pass device with a driving voltage. The leakage current compensation circuit may be configured to receive a leakage current of the pass device and may be configured to forward said leakage current as a bias current to said control circuit.

Claims

1. A solid-state circuit comprising: a pass device having a first terminal, a second terminal and a drive terminal, wherein the first terminal of the pass device is coupled with an input terminal of the solid-state circuit, and wherein the second terminal of the pass device is coupled with an output terminal of the solid-state circuit; a control circuit coupled with the drive terminal of the pass device and configured to drive the pass device with a driving voltage; and a leakage current compensation circuit configured to receive a leakage current of the pass device and to forward said leakage current as a bias current to said control circuit.

2. The solid-state circuit of claim 1, wherein the leakage current compensation circuit is coupled to the second terminal of the pass device to receive the leakage current of the pass device.

3. The solid-state circuit of claim 1, wherein the control circuit comprises a differential amplifier stage configured to generate an intermediate signal based on a difference between a reference signal and a feedback signal indicative of an output voltage at the output terminal of the solid-state device.

4. The solid-state circuit of claim 3, wherein the leakage current compensation circuit is configured to forward the leakage current to said differential amplifier stage.

5. The solid-state circuit of claim 3, wherein the control circuit comprises a further amplifier stage coupled between the differential amplifier stage and the pass device, and wherein the leakage current compensation circuit is configured to forward the leakage current to said differential amplifier stage and said further amplifier stage.

6. The solid-state circuit of claim 1, wherein the leakage current increases as a function of temperature.

7. The solid-state circuit of claim 1, wherein the control circuit is characterized by a minimum bias current, and wherein the solid-state circuit is configured to provide only the leakage current to the control circuit when the leakage current is greater than the minimum bias current.

8. The solid-state circuit of claim 7, wherein the solid-state circuit is configured to provide the minimum leakage current to the control circuit when the leakage current is smaller than the minimum bias current.

9. A method for operating a solid-state circuit, wherein the solid-state circuit comprises a pass device having a first terminal, a second terminal and a drive terminal, wherein the first terminal of the pass device is coupled with an input terminal of the solid-state circuit, and wherein the second terminal of the pass device is coupled with an output terminal of the solid-state circuit, wherein the solid-state circuit comprises a control circuit coupled with the drive terminal of the pass device, the method comprising driving, by the control circuit, the pass device with a driving voltage; receiving, by a leakage current compensation circuit, a leakage current of the pass device; and forwarding, by the leakage current compensation circuit, said leakage current as a bias current to said control circuit.

10. The method of claim 9, wherein the leakage current compensation circuit is coupled to the second terminal of the pass device to receive the leakage current of the pass device.

11. The method of claim 9, wherein the control circuit comprises a differential amplifier stage for generating an intermediate signal based on a difference between a reference signal and a feedback signal indicative of an output voltage at the output terminal of the solid-state device, the method further comprising forwarding, by the leakage current compensation circuit, the leakage current to said differential amplifier stage.

12. The method of claim 11, wherein the control circuit comprises a further amplifier stage coupled between the differential amplifier stage and the pass device, and wherein the method further comprises forwarding, by the leakage current compensation circuit, the leakage current to said differential amplifier stage and said further amplifier stage.

13. The method of claim 9, wherein the leakage current increases as a function of temperature.

14. The method of claim 9, wherein the control circuit is characterized by a minimum bias current, and wherein the method further comprises providing only the leakage current to the control circuit when the leakage current is greater than the minimum bias current.

15. The method of claim 14, wherein the method further comprises providing the minimum leakage current to the control circuit when the leakage current is smaller than the minimum bias current.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar or identical elements, and in which

(2) FIG. 1 shows a diagram showing leakage current versus temperature;

(3) FIG. 2 shows currents and voltages in a solid-state circuit;

(4) FIG. 3 shows a circuit diagram of a linear regulator;

(5) FIG. 4 shows another diagram showing leakage currents and bias currents versus temperature;

(6) FIG. 5 shows another circuit diagram of a linear regulator, of the present disclosure;

(7) FIG. 6A and 6B show two diagrams showing currents versus temperature;

(8) FIG. 7A and 7B show two further diagrams showing currents versus temperature; and

(9) FIG. 8 shows a flowchart for a method of operating a solid-state circuit.

DETAILED DESCRIPTION

(10) FIG. 1 shows a diagram 1 showing leakage current versus temperature, of the prior art. All solid-state circuits exhibit leakage current. As shown by FIG. 1, the leakage current I.sub.LEAK 100 varies non-linearly with temperature T. To be more specific, the leakage current is illustrated in diagram 1 as a continuous, increasing and convex function of the temperature of the solid-state circuit.

(11) FIG. 2 shows currents and voltages in a solid-state circuit, of the prior art. More specifically, FIG. 2 depicts a schematic circuit diagram of a solid-state circuit 200 which is connected between a supply voltage V.sub.DD and ground GND. As illustrated in FIG. 2, to properly operate the solid-state circuit 200, a bias current I.sub.BIAS and a current I.sub.Q must be provided. I.sub.BIAS may generally refer to the current needed to operate the circuit. The current I.sub.Q is based on a leakage current I.sub.LEAK at the worst-case operating temperature. The current from the supply (I.sub.VDD) may be seen as the sum of I.sub.BIAS and I.sub.Q. In order for the solid-state circuit to operate correctly, there should be compensation for the leakage current I.sub.LEAK. The corresponding power may be described with the following formula:
P.sub.LOSS=V.sub.DD×(I.sub.QI.sub.LEAK).

(12) A specific example of a solid-state circuit is a linear regulator. FIG. 3 shows a circuit diagram of a linear regulator 300 which is embodied as a low-dropout (LDO) regulator, of the prior art. The exemplary linear regulator 300 comprises a pass device 31, a control circuit 30, and a leakage current compensation unit 36. The pass device 31 may have a first terminal, a second terminal and a drive terminal, wherein the first terminal of the pass device 31 is coupled with an input terminal of the linear regulator 300, and wherein the second terminal of the pass device 31 is coupled with an output terminal of the linear regulator 300. The control circuit 30 may be coupled with the drive terminal of the pass device 31 and may be configured to drive the pass device 31 with a driving voltage. In the illustrated example, the leakage current compensation unit 36 is coupled between the output terminal of the linear regulator 300 and ground.

(13) In the example of FIG. 3, the control circuit 30 comprises a differential amplifier stage 32, a further amplifier stage 33, and an optional driver stage 34. The differential amplifier stage 32 may be configured to generate an intermediate signal based on a difference between a reference signal V.sub.REF and a feedback signal indicative of an output voltage V.sub.OUT at the output terminal of the linear regulator 300. The linear regulator 300 may further comprise a feedback network 35 for generating said feedback signal based on the output voltage V.sub.OUT. As can be seen, the differential amplifier stage 32 and the further amplifier stage 33 are driven by respective bias currents IBIAS_1 and IBIAS_2 which are derived from the output terminal of the linear regulator 300. Also, the driver 34 may be driven by a respective bias current which is derived from the output terminal of the linear regulator 300 (not shown in FIG. 3).

(14) The linear regulator 300 may employ direct feedback, as the bias currents for the control and compensation circuits 32, 33 are provided directly from the output of the LDO. This has many advantages, including superior noise immunity. Further, the main pass element(s), shown as a single device S1 31 in FIG. 3, is the major source of the LDO's leakage current I.sub.LEAK. Since there should be compensation for I.sub.LEAK, the linear regulator 300 has the I.sub.LEAK compensation circuit 36, which essentially sources/sinks the leakage current I.sub.LEAK to ground.

(15) FIG. 4 shows another diagram showing leakage currents and bias currents versus temperature, of the prior art. In particular, FIG. 4 shows the leakage current I.sub.LEAK 400 and curves for the LDO shown in FIG. 3 as a function of temperature. Again, current I.sub.Q may be seen as the sum of the leakage current I.sub.LEAK and the bias currents I.sub.BIAS1 and I.sub.BIAS2 410.

(16) FIG. 5 shows another circuit diagram of a linear regulator 510, wherein a leakage current compensation circuit 500 sources the bias currents I.sub.BIAS1 and I.sub.BIAS2, in the present disclosure. In the example of FIG. 5, the control circuit 50 comprises a differential amplifier stage 52, a further amplifier stage 53, and an optional driver stage 54 for driving pass device 51. The differential amplifier stage 52 may be configured to generate an intermediate signal based on a difference between a reference signal V.sub.REF and a feedback signal indicative of an output voltage V.sub.OUT at the output terminal of the linear regulator 510. The linear regulator 510 may further comprise a feedback network 55 for generating said feedback signal based on the output voltage V.sub.OUT.

(17) As can be seen, the differential amplifier stage 52 and the further amplifier stage 53 are driven by respective bias currents IBIAS_1 and IBIAS_2 which are generated by the leakage current compensation circuit 500 which is configured to receive a leakage current of the pass device 51 and to forward said leakage current as a bias current to the differential amplifier stage 52 and the further amplifier stage 53 of control circuit 50. Also, the driver 54 may be driven by a respective bias current which generated by leakage current compensation circuit 500 (not shown in FIG. 5).

(18) As mentioned above, the present invention increases the bias current without increasing I.sub.Q. This may be achieved by integrating the I.sub.LEAK compensation circuit with the I.sub.BIAS source. The leakage current, instead of being sourced directly to GND, is further used as a bias current source. There is an added benefit in that the leakage current may increase as a function of temperature. At the same time, the transconductance may decrease as a function of temperature. By using the leakage current as a bias current source, the bias current can be increased as the temperature increases, which is very beneficial. The result is greater LDO performance, including improving dynamic response, increase noise immunity over a greater bandwidth, and reducing noise on the output.

(19) FIG. 6A and B show two diagrams showing currents versus temperature. Specifically, FIG. 6A and 6B depict a comparison between the prior art circuit of FIG. 2 and the circuit in FIG. 5 in terms of I.sub.Q, I.sub.LEAK, and I.sub.BIAS. By comparing the I.sub.BIAS 610 in FIG. 6A (relating to the circuit in FIG. 2) with the I.sub.BIAS 620 in FIG. 6B (relating to the circuit in FIG. 5), one can see that it is significantly greater in in FIG. 6B without increasing I.sub.Q. Hence, this would result in the highest performance while maintaining an equivalent I.sub.Q.

(20) FIG. 7A and 7B show two further diagrams showing currents versus temperature. Again, FIG. 7A relates to the prior art circuit in FIG. 2, and FIG. 7B relates to the circuit in FIG. 5. The diagrams in FIG. 7A and 7B illustrate how performance can be improved by increasing I.sub.BIAS and reducing I.sub.Q. As one can see, there are two sections, one section where the bias current is lower than the leakage current 720, and one section where the bias current is greater than the leakage current 710. During the period when the bias current is greater than the leakage current 710, the following relations hold:
When (IBIAS_1+IBIAS_2)>ILEAK IQ=(IBIAS_1+IBIAS_2).

(21) During the period when the bias current is less than the leakage current 720, the following relations hold:
When (IBIAS_1+IBIAS_2)<ILEAK IQ=IBIAS_1+IBIAS_2=ILEAK

(22) This results in minimizing I.sub.Q while still increasing I.sub.BIAS.

(23) FIG. 8 shows 800, a method for operating a solid-state circuit. The steps include 810, providing a solid-state circuit comprising a pass device having a first terminal, a second terminal and a drive terminal, and a control circuit coupled with the drive terminal. The steps also include 820, driving, by the control circuit, the pass device with a driving voltage. The steps also include 830, receiving, by a leakage current compensation circuit, a leakage current of the pass device. The steps also include 840, forwarding, by the leakage current compensation circuit, the leakage current as a bias current to the control circuit.

(24) It should be noted that the description and drawings merely illustrate the principles of the proposed methods and systems. Those skilled in the art will be able to implement various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and embodiment outlined in the present document are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the proposed methods and systems. Furthermore, all statements herein providing principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.