Current-Mode Driver with Built-In Continuous-Time Linear Equalization

Patent metadata

Field	Value
Publication number	US-2016248518-A1
Application number	US-201514631272-A
Country	US
Kind code	A1
Filing date	Feb 25, 2015
Priority date	Feb 25, 2015
Publication date	Aug 25, 2016
Grant date	—

Abstract

According to one embodiment of the present disclosure, a current-mode driver with built-in CTLE provides signal correction for a transmitter. The current-mode driver includes a digital current source operable to use a data signal to produce a main current signal. The current-mode driver also includes a filtering circuit comprising a resistor and a capacitor. The filtering circuit is operable to receive a negative data signal and produce a filtered data signal. The filtering circuit may be tuned to produce a zero at a pole frequency in the filtered data signal that compensates for signal degradation caused by the optical transmitter. The current-mode driver also includes an analog current source coupled in parallel to the digital current source, wherein the analog current source is operable to generate a subtraction current signal proportional to the filtered data signal. The subtraction current signal combined with the main current signal are operable to drive the transmitter.

First claim

1 . A current-mode driver with built-in continuous-time linear equalization (CTLE) for a transmitter, comprising:
a digital current source operable to use a data signal to produce a main current signal; a filtering circuit comprising a resistor and a capacitor, the filtering circuit operable to receive a negative data signal and produce a filtered data signal, wherein the filtering circuit is tuned to produce a zero at a pole frequency in the filtered data signal that compensates for signal degradation caused by an optical transmitter; and an analog current source coupled in parallel to the digital current source, wherein the analog current source is operable to generate a subtraction current signal proportional to the filtered data signal, the subtraction current signal combined with the main current signal are operable to drive the transmitter.

2 . The current-mode driver of claim 1 , wherein the transmitter is a vertical-cavity surface-emitting laser (VCSEL).

3 . The current-mode driver of claim 2 , further comprising:
a DC current source in parallel with the digital current source and the analog current source, wherein the DC current source is operable to bias the VCSEL; and a termination resistor coupled to the digital current source and the analog current source, the termination resistor operable to maximize the power transfer between the current-mode driver and the VCSEL.

4 . The current-mode driver of claim 1 , wherein the resistor is a variable resistor and the capacitor is a variable capacitor.

5 . The current-mode driver of claim 4 , wherein the variable resistor and variable capacitor are dynamically tuned in response to temperature changes in the transmitter.

6 . The current-mode driver of claim 4 , wherein the variable resistor and variable capacitor are dynamically tuned in response to frequency changes in the data signal.

7 . A method comprising:
receiving a data signal at a digital current source, wherein the digital current source is operable to use the data signal to produce a main current signal; receiving, at a filtering circuit, a negative data signal, wherein the filtering signal comprises a resistor and a capacitor; filtering, by the filtering circuit, the negative data signal according to characteristics of the resistor and the capacitor to create a filtered data signal; generating, with an analog current source in parallel with the digital current source, a subtraction current signal, wherein the subtraction current signal is proportional to the filtered data signal; combining the subtraction current signal with the main current signal to produce a compensation signal operable to drive a transmitter.

8 . The method of claim 7 , wherein the filtering circuit is tuned to produce a zero at a pole frequency of the filtering circuit that compensates for bandwidth limitations of the transmitter.

9 . The method of claim 7 , wherein the transmitter is a vertical-cavity surface-emitting laser (VCSEL).

10 . The method of claim 9 , further comprising:
biasing the transmitter with a DC current source that is in parallel with the analog current source and the digital current source.

11 . The method of claim 7 , wherein the resistor and the capacitor are operable to create a low-pass filter.

12 . The method of claim 7 , wherein the resistor is a variable resistor and the capacitor is a variable capacitor.

13 . The method of claim 12 , wherein the variable resistor and variable capacitor are dynamically tuned in response to temperature changes in the transmitter.

14 . An apparatus comprising:
a digital current source operable to use a data signal to produce a main current signal; a filtering circuit comprising a resistor and a capacitor, wherein the filtering circuit receives a negative data signal and generates a filtered data signal according to characteristics of the resistor and capacitor; and an analog current source coupled in parallel to the digital current source, wherein the analog current source is operable to generate a subtraction current signal proportional to the filtered data signal, the subtraction current signal combined with the main current signal are operable to drive a transmitter.

15 . The apparatus of claim 14 , wherein the filtering circuit is tuned to produce a zero at a pole frequency of the filtering circuit that compensates for signal degradation caused by a vertical-cavity surface-emitting laser (VCSEL).

16 . The apparatus of claim 14 , wherein the transmitter is a vertical-cavity surface-emitting laser (VCSEL).

17 . The apparatus of claim 16 , further comprising:
a DC current source coupled to the digital current source and the analog current source, wherein the DC current source is configured to bias the VCSEL; and a termination resistor coupled to the output of the analog current source and DC current source.

18 . The apparatus of claim 14 , wherein the resistor and the capacitor are configured to create a low-pass filter.

19 . The apparatus of claim 14 , wherein the resistor is a variable resistor and the capacitor is a variable capacitor.

20 . The apparatus of claim 19 , wherein the variable resistor and variable capacitor are dynamically tuned in response to temperature changes in the transmitter.

Assignees

• Fujitsu Ltd

Inventors

• Parikh Samir

Classifications

• H04B10/503

  Laser transmitters · CPC title

• H04B10/564 Primary

  Power control · CPC title

• H04L25/03006

  Arrangements for removing intersymbol interference · CPC title

• H04B10/504

  using direct modulation · CPC title

• H04L25/03343

  Arrangements at the transmitter end · CPC title