Impedance matched CMOS transimpedance amplifier for high-speed fiber optic communications

• US 6,037,841 A
• Filed: 10/07/1998
• Issued: 03/14/2000
• Est. Priority Date: 10/07/1997
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Applied Micro Circuits Corporation (MACOM Technology Solutions Holdings, Inc.)
• Inventors: Tanji, Todd M., Stronczer, John J.
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Nguyen, Patricia T.
• Application Number:
  US09/168,027
• Time in Patent Office: 524 Days
• Field of Search: 330/308, 250/214 A
• US Class Current: 330/308
• CPC Class Codes: H03F 3/082 with FET's H03F3/085 takes precedence

Abstract

A transimpedance amplifier according to the present invention is designed for high-speed fiber optic communications. The transimpedance amplifier preferably includes an input stage, a second stage and a bias generator. The input stage is operably coupled to the second stage and has an input impedance. The second stage has an output impedance. The bias generator is operably coupled to the input stage and the second stage, and operates to bias the input stage and second stage such that the input impedance substantially matches the output impedance. In this manner, the input and output impedances of a transimpedance amplifier of a fiber optics communication receiver are controllable to a desired impedance for interfacing with a transmission line.

Claims

1. A transimpedance amplifier for use in a fiber optic receiver, said transimpedance amplifier comprising:

an input stage having an input impedance;

a second stage operably connected to said input stage and having an output impedance; and

a bias generator operably connected to said input stage and to said second stage, wherein said bias generator biases said input stage and said second stage such that said input impedance substantially matches said output impedance.

2. The amplifier of claim 1, further comprising a biasing circuit, said biasing circuit being operably connected to said input stage and to said second stage.

3. The amplifier of claim 2, wherein said biasing circuit provides a bias current for said input stage.

4. The amplifier of claim 1, wherein said bias generator substantially fixes said input impedance and said output impedance to a desired value for transmission line interfacing.

5. The amplifier of claim 4, wherein said desired value is less than 100 ohms.

6. The amplifier of claim 4, wherein said desired value is about 50 ohms.

7. The amplifier of claim 5, wherein said input stage is biased with a low capacitance, p-channel current source circuit.

8. The amplifier of claim 1, wherein said transimpedance amplifier is fabricated using CMOS technology.

9. A fiber optic receiver comprising:

a detector wherein said detector detects optical energy from an optical fiber and produces an output representative of the detected optical energy; and

a transimpedance amplifier, wherein said transimpedance amplifier comprises;

an input stage, wherein said input stage receives said output and wherein said input stage has an input impedance;

a second stage operably coupled to said input stage and having an output impedance; and

bias generating means operably coupled to said input stage and said second stage, wherein said bias generating means biases said input stage and said second stage such that said input impedance substantially matches said output impedance.

10. The fiber optic receiver of claim 9, further comprising a post amplifier operably coupled to said transimpedance amplifier.

11. The fiber optic receiver of claim 9, wherein said bias generating means substantially fixes said input impedance and said output impedance to a desired value for transmission line interfacing.

12. The fiber optic receiver of claim 11, wherein said value is less than 100 ohms.

13. The fiber optic receiver of claim 9, wherein said input stage is biased with a low capacitance, p-channel current source circuit.

14. The fiber optic receiver of claim 11 wherein said value is about 50 ohms.

15. The fiber optic receiver of claim 9, wherein said transimpedance amplifier is fabricated using CMOS technology.

16. A transimpedance amplifier for use in a fiber optic receiver, said transimpedance amplifier comprising:

an input stage including a first transistor and a second transistor operably coupled to said first transistor, wherein said input stage has an input impedance defined by a transconductance of said first transistor;

a second stage operably coupled to said input stage, said second stage including a third transistor and a fourth transistor operably coupled to said third transistor, wherein said second stage has an output impedance defined by a transconductance of said third transistor; and

a bias generator operably coupled to said input stage and said second stage, wherein said bias generator biases said input stage and said second stage to substantially fix said input impedance and said output impedance to a same desired value.

17. The amplifier of claim 16, wherein said desired value is selected for transmission line interfacing.

18. The amplifier of claim 17, wherein said desired value is less than 100 ohms.

19. The amplifier of claim 17, wherein said desired value is about 50 ohms.