Digital Automatic Gain Control Apparatus and Method in Burst Mode Optical Receiver

• US 20100014866A1
• Filed: 12/05/2006
• Published: 01/21/2010
• Est. Priority Date: 12/05/2005
• Status: Active Grant

• Current Assignee: Electronics and Telecommunications Research Institute, Korea Advanced Institute of Science and Technology
• Original Assignee: Korea Advanced Institute of Science and Technology
• Inventors: Lee, Sang-Gug, Kang, Ho-Yong, Le, Quan, Kim, Bong-Tae, Kwon, Yool, Choi, Hyun-Kyun
• Granted Patent: US 8,660,439 B2
• Time in Patent Office: Days
• US Class Current: 398/99
• CPC Class Codes: H03G 3/3084 in receivers or transmitters for electromagnetic waves other than radiowaves, e.g. lightwaves H03G3/32, H03G3/34 take precedence
• CPC Class Codes: H04B 10/66 Non-coherent receivers, e.g. using direct detection
• CPC Class Codes: H04B 10/6931 Automatic gain control of the preamplifier

Abstract

A transimpedance amplifier for a burst mode optical communication converts a burst current signal into differential output voltage signals. Using a multi-level digital AGC mechanism, the transimpedance amplifier is rapidly adapted to a burst signal whose amplitude varies in a wide range. By using an adaptive level detection method, a multi-level digital AGC can be implemented without using ADC. In addition, because the transimpedance amplifier uses a selective reset generation scheme that performs a reset operation for itself after a high power burst, a burst mode operation can be performed without external reset signals. Accordingly, the transimpedance amplifier can be integrated with an optical detector within a TO-can. Furthermore, the transimpedance amplifier can have the burst mode capability and the best sensitivity.

Claims

1. A digital automatic gain control method in a burst mode optical receiver having an optical detector and a transimpedance amplifier for converting an output current signal of the optical detector into a voltage signal, the digital automatic gain control method comprising:

detecting a bottom holding level of the outputted voltage signal when a burst begins;

generating a reset signal using a reference voltage generated according to an output signal of the transimpedance amplifier;

comparing the detected bottom holding level with an input signal; and

controlling a gain of the transimpedance amplifier by generating an automatic gain control signal according to the comparison result.

2. The digital automatic gain control method according to claim 1, further comprising:

detecting a new bottom holding level when the reset signal is generated;

comparing the detected new bottom holding level with the reference voltage; and

controlling a generation of another automatic gain control signal according to the comparison result, wherein the comparing operation and the reset signal generating operation are repeated until the comparison result becomes low.

3. The digital automatic gain control method according to claim 1, wherein in the controlling of the gain of the transimpedance amplifier, when the detected bottom holding level is lower than the input signal and a high signal is outputted, at least one switch is closed by outputting one automatic gain control signal of a high level and the gain of the transimpedance amplifier is reduced.

4. The digital automatic gain control method according to claim 3, wherein in the controlling of the generation of the automatic gain control signal, when the new bottom holding level is lower than the input signal, another switch is closed by outputting the another automatic gain control signal of a high level and the gain of the transimpedance amplifier is further reduced.

5. The digital automatic gain control method according to claim 1, wherein the generating of the reset signal using the reference voltage comprises:

generating a tracking voltage (Vmid_RC) of the transimpedance amplifier;

generating a reference voltage (Vref_quarter) between the bottom holding level and an output level of a dummy amplifier through a resistive divided voltage; and

comparing the reference voltage (Vref_quarter) with the tracking voltage (Vmid_RC) and generating a reset signal after a burst.

6. The digital automatic gain control method according to claim 5, further comprising stopping the generation of the reset signal until a next burst arrives, when a circuit for detecting the bottom holding level is reset after the generation of the reset signal and a reset enable signal of a low level is generated.

7. The digital automatic gain control method according to claim 6, wherein the reference voltage (Vref_quarter) has a middle value of the output signal of the transimpedance amplifier, the middle value being lower than Vdark by ¼

.

8. A digital automatic gain control apparatus in a burst mode optical receiver having an optical detector and a transimpedance amplifier for converting an output current signal of the optical detector into a voltage signal, the digital automatic gain control apparatus comprising:

an automatic gain controller for detecting a bottom holding level of the outputted voltage signal when a burst begins, controlling a gain of the transimpedance amplifier by generating at least one automatic gain control signal according to the detected bottom holding level, and generating a reset signal using a reference voltage generated according to an output signal of the transimpedance amplifier;

a comparator for comparing the detected bottom holding level with an input voltage, generating a first comparison signal notifying if the automatic gain controller is enabled to generate the reset signal, generating a second comparison signal to enable the reset signal to be generated using the reference voltage, and comparing the detected bottom holding level with the input voltage to output a third comparison signal to enable the automatic gain controller to generate the automatic gain control signal; and

a reference voltage generator for generating the reference voltage to the comparator.

9. The digital automatic gain control apparatus according to claim 8, wherein the automatic gain controller comprises:

a bottom holding circuit for detecting the bottom holding level through the output signal of the transimpedance amplifier;

a logic controller for generating the reset signal and the at least one automatic gain control signal according to the comparison signals; and

a feedback circuit for controlling the gain of the transimpedance amplifier through the at least one automatic gain control signal.

10. The digital automatic gain control apparatus according to claim 9, wherein the logic controller generates the reset signal to the bottom holding circuit when the first and second comparison signals are high.

11. The digital automatic gain control apparatus according to claim 9, wherein the logic controller generates one automatic gain control signal of a high level to close at least one switch when the third comparison signal is high, and reduces the gain of the transimpedance amplifier.

12. The digital automatic gain control apparatus according to claim 11, wherein the logic controller closes another switch by generating another automatic gain control signal of a high level when the third comparison signal compared according to a new bottom holding level detected by the bottom holding circuit is high after the bottom holding circuit is reset, and further reduces the gain of the transimpedance amplifier.

13. The digital automatic gain control apparatus according to claim 9, wherein the logic controller stops the generation of the reset signal until a next burst arrives, when the first comparison signal is low after the bottom holding circuit is reset.

14. The digital automatic gain control apparatus according to claim 9, wherein the reference voltage generator generates a tracking voltage (Vmid_RC) according to the output signal of the transimpedance amplifier, and generates a reference voltage (Vref_quarter) between the bottom holding level and an output level of a dummy amplifier through a resistive divided voltage.

15. The digital automatic gain control apparatus according to claim 14, wherein the comparator compares the reference voltage (Vref_quarter) with the tracking voltage (Vmid_RC) after the burst, and outputs the second comparison signal to enabling the reset signal to be generated.

16. The digital automatic gain control apparatus according to claim 15, wherein the reference voltage (Vref_quarter) has a middle value of the output signal of the transimpedance amplifier, the middle value being lower than Vdark by ¼

.