Source follower

Patent metadata

Field	Value
Publication number	US-10476447-B2
Application number	US-201715810942-A
Country	US
Kind code	B2
Filing date	Nov 13, 2017
Priority date	Dec 8, 2016
Publication date	Nov 12, 2019
Grant date	Nov 12, 2019

Abstract

A source follower with an input node and an output node includes a first transistor, a second transistor, and a DC (Direct Current) tracking circuit. The first transistor has a control terminal, a first terminal coupled to a first node, and a second terminal coupled to a second node. The second transistor has a control terminal, a first terminal coupled to a ground voltage, and a second terminal coupled to the first node. The DC tracking circuit sets the second DC voltage at the second node to a specific level. The specific level is determined according to the first DC voltage at the first node. The output node of the source follower is coupled to the first node.

First claim

What is claimed is:

1. A source follower, comprising:
a first transistor, comprising a control terminal, a first terminal coupled to an output node of the source follower, and a second terminal coupled to a DC (Direct Current) tracking circuit; and
a second transistor, comprising a control terminal, a first terminal coupled to ground, and a second terminal coupled to the output node;
wherein the DC tracking circuit is arranged for comparing a first voltage of the output node with a voltage to generate a control signal to a control terminal of a fourth transistor to provide a second voltage to the second terminal of the first transistor.

2. The source follower as claimed in claim 1 , wherein the second voltage is substantially equal to two times the first voltage.

3. The source follower as claimed in claim 1 , wherein the DC tracking circuit comprises an open-loop operational amplifier, a closed-loop operational amplifier, or a linear regulator.

4. The source follower as claimed in claim 1 , wherein an input node of the source follower is coupled to the control terminal of the first transistor, and a bias voltage is coupled to the control terminal of the second transistor.

5. The source follower as claimed in claim 4 , wherein the first transistor and the second transistor are NMOS transistors (N-type Metal-Oxide-Semiconductor Field-Effect Transistors).

6. The source follower as claimed in claim 1 , wherein the DC tracking circuit comprises:
a first operational amplifier, comprising a first input terminal for receiving a first reference voltage, a second input terminal, and an output terminal;
the fourth transistor, comprising the control terminal coupled to the output terminal of the first operational amplifier, and a second terminal coupled to a supply voltage; and
a second operational amplifier, comprising a first input terminal for receiving the first reference voltage, a second input terminal for receiving a second reference voltage, and an output terminal coupled to an input node of the source follower.

7. The source follower as claimed in claim 6 , wherein the DC tracking circuit further comprises:
a third transistor, comprising a control terminal coupled to the output terminal of the first operational amplifier, a first terminal, and a second terminal coupled to the supply voltage;
wherein the fourth transistor further comprises a first terminal coupled to the first transistor.

8. The source follower as claimed in claim 7 , wherein the DC tracking circuit further comprises:
a first resistor, coupled between the fifth node and the third node; and
a second resistor, coupled between the third node and the ground voltage.

9. The source follower as claimed in claim 7 , wherein both the first voltage and the second reference voltage are equal to the first reference voltage.

10. The source follower as claimed in claim 7 , wherein the third transistor and the fourth transistor are NMOS transistors (N-type Metal-Oxide-Semiconductor Field-Effect Transistors).

11. The source follower as claimed in claim 7 , wherein a DC component of an output voltage at the output node of the source follower is fed back to the second reference voltage.

12. The source follower as claimed in claim 1 , wherein an input node of the source follower is coupled to the control terminal of the second transistor, and a bias voltage is coupled to the control terminal of the first transistor.

13. The source follower as claimed in claim 12 , wherein the first transistor and the second transistor are PMOS transistors (P-type Metal-Oxide-Semiconductor Field-Effect Transistors).

14. A source follower with an input node and an output node, comprising:
a first transistor, wherein the first transistor has a control terminal, a first terminal coupled to a first node, and a second terminal coupled to a supply voltage;
a second transistor, wherein the second transistor has a control terminal, a first terminal coupled to a second node, and a second terminal coupled to the first node; and
a DC (Direct Current) tracking circuit, comparing a first voltage of the output node with a voltage to general a control signal to a control terminal of a fourth transistor to provide a second DC voltage at the second node to a specific level;
wherein the output node of the source follower is coupled to the first node.

15. The source follower as claimed in claim 14 , wherein the second DC voltage is substantially equal to two times the first DC voltage minus the supply voltage.

16. The source follower as claimed in claim 14 , wherein the DC tracking circuit is implemented with an open-loop operational amplifier, a closed-loop operational amplifier, or a linear regulator.

17. The source follower as claimed in claim 14 , wherein the input node of the source follower is coupled to the control terminal of the first transistor, and a bias voltage is coupled to the control terminal of the second transistor.

18. The source follower as claimed in claim 17 , wherein the first transistor and the second transistor are NMOS transistors (N-type Metal-Oxide-Semiconductor Field-Effect Transistors).

19. The source follower as claimed in claim 14 , wherein the input node of the source follower is coupled to the control terminal of the second transistor, and a bias voltage is coupled to the control terminal of the first transistor.

20. The source follower as claimed in claim 19 , wherein the first transistor and the second transistor are PMOS transistors (P-type Metal-Oxide-Semiconductor Field-Effect Transistors).

Assignees

• Mediatek Inc

Inventors

• Kuo Che-Hsun

Classifications

• H03F1/0255

  by using a signal derived from the output signal · CPC title

• H03F3/193

  with field-effect devices (H03F3/195 takes precedence) · CPC title

• H03F1/0233 Primary

  by using a signal derived from the output signal, e.g. bootstrapping the voltage supply · CPC title

• H03F2200/102

  A non-specified detector of a signal envelope being used in an amplifying circuit · CPC title

• H03K19/018507

  Interface arrangements · CPC title