Non-linear filter for dml

Abstract

A circuit is disclosed having a component having repeatable distortion characteristics; and a drive circuit for providing a drive signal and comprising a non-linear filter for pre-compensating for distortion introduced by the component having repeatable distortion characteristics in response to the drive signal, the distortion having a non-linear response to the drive signal.

What is claimed is: 
     
         1 . A circuit comprising:
 a component having repeatable distortion characteristics; and   a drive circuit for providing a drive signal and comprising a non-linear filter having at least a tap for pre-compensating for distortion introduced by the component having repeatable distortion characteristics in response to the drive signal, the distortion having a non-linear response to the drive signal.   
     
     
         2 . A circuit according to  claim 1  wherein the component comprises a Directly Modulated Laser (DML). 
     
     
         3 . A circuit according to  claim 2  wherein the DML comprises a Vertical Cavity Surface Emitting Laser (VCSEL). 
     
     
         4 . A circuit according to  claim 2  wherein the DML comprises a Distributed FeedBack (DFB) laser. 
     
     
         5 . A circuit according to  claim 3  wherein the DML is operated at at least 25 Gbps. 
     
     
         6 . A circuit according to  claim 4  wherein the non-linear filter comprises a non-linear Finite Impulse Response (FIR) filter having at least 2 weights for application at each delayed tap and supporting at least one delayed tap. 
     
     
         7 . A circuit according to  claim 4  wherein the non-linear filter comprises a non-linear Finite Impulse Response (FIR) filter having at least 2 weights for application at each delayed tap and supporting at least 3 delayed taps. 
     
     
         8 . A circuit according to  claim 1  wherein the non-linear filter comprises a non-linear Finite Impulse Response (FIR) filter having at least 2 weights for application at each delayed tap and supporting filtering of both a rising edge, low to high signal level response and a falling edge, high to low signal level response. 
     
     
         9 . A circuit according to  claim 8  comprising:
 for each tap a first input port for receiving a first weight, a second input port for receiving a second other weight, a switch for switching between the first weight and the second weight, and a weighting circuit for weighting of a signal within the tap to produce a tap output, tap output signals from different taps combined to form the drive signal. 
 
     
     
         10 . A circuit according to  claim 8  comprising:
 for each tap a first input port for receiving a first weight, a second input port for receiving a second other weight, a scaling circuit for scaling the first weight and the second weight, and a weighting circuit for weighting of a signal within the tap to produce a tap output, tap output signals from different taps combined to form the drive signal. 
 
     
     
         11 . A circuit according to  claim 1  wherein the non-linear filter comprises a non-linear Finite Impulse Response (FIR) filter having greater than 2 weights at each delayed tap supporting filtering of a complex amplitude dependent non-linear distortion for a signal with a modulation scheme having greater than 2 amplitude levels of consequence for a given data symbol, such as PAM4 or 4-Level Pulse Amplitude Modulation. 
     
     
         12 . A circuit according to  claim 11  consisting of an analogue filter circuit. 
     
     
         13 . A circuit according to  claim 12  wherein the circuit is implemented in an integrated semiconductor. 
     
     
         14 . A circuit according to  claim 11  comprising:
 for each tap a first input port for receiving a first weight, a second input port for receiving a second other weight, a scaling circuit for scaling the first weight and the second weight, and a weighting circuit for weighting of a signal within the tap to produce a tap output, tap output signals from different taps combined to form the drive signal. 
 
     
     
         15 . A method comprising:
 providing a drive current for driving a component;   filtering the drive current with a non-linear filter to provide pre-compensated drive current pre-compensated for distortion in a signal resulting from driving the component with the drive current, wherein an output signal from the component in response to the pre-compensated drive current has reduced distortion and better approximates an ideal transmit signal for an intended modulation.   
     
     
         16 . A method according to  claim 15  wherein the component comprises a Directly Modulated Laser (DML). 
     
     
         17 . A method according to  claim 16  wherein the directly modulated laser comprises a Vertical Cavity Surface Emitting Laser (VCSEL). 
     
     
         18 . A method according to  claim 16  wherein the directly modulated laser comprises a Distributed FeedBack (DFB) laser. 
     
     
         19 . A method according to  claim 18  wherein filtering is performed with an analogue filter. 
     
     
         20 . A method according to  claim 15  wherein the analogue filter is implemented in semiconductor. 
     
     
         21 . A method according to  claim 15  wherein the non-linear filter comprises a non-linear FIR filter. 
     
     
         22 . A method according to  claim 15  wherein filtering corrects for both a rising edge, low to high signal level response, and a falling edge, high to low signal level response. 
     
     
         23 . A circuit comprising:
 an input port for receiving a first signal;   a plurality of taps, each tap comprising an input port for receiving a tap input signal, a first input port for receiving a first weight, a second input port for receiving a second other weight, and a scaling circuit for scaling an applied weighting based on the first weight and the second weight to scale the tap signal, the scaled tap signal for modifying the first signal.   
     
     
         24 . A circuit according to  claim 23  wherein the scaling circuit comprises a switching circuit for switching between the different weights to select one weight for application at a first time and another weight for application at another time within a same signal to be filtered. 
     
     
         25 . A circuit according to  claim 23  wherein the scaling circuit comprises a switching circuit for switching between the different weights to select one weight for application at a first time and another weight for application at another time in dependence upon a content of the signal to be filtered. 
     
     
         26 . A circuit according to  claim 23  comprising a summer for summing an output of each of the plurality of taps. 
     
     
         27 . A circuit comprising:
 an input port for receiving a first signal;   a plurality of taps, each tap comprising an input port for receiving a tap input signal, a first input port for receiving a first weight, a second input port for receiving a second other weight, and a scaling circuit for scaling an applied weighting between the first weight and the second weight to scale the tap signal, the scaled tap signal for modifying the first signal.   
     
     
         28 . A circuit comprising:
 an input port for receiving a first signal;   a plurality of taps, each tap comprising an input port for receiving a tap input signal, a plurality of input ports each for receiving a weight, and a scaling circuit for scaling an applied weighting based on the received weights to scale the tap signal, the scaled tap signal for modifying the first signal.   
     
     
         29 . A circuit according to  claim 28  wherein the scaling circuit comprises a switching circuit for switching between the different weights to select one weight for application at a first time and another weight for application at another time within a same signal to be filtered. 
     
     
         30 . A circuit according to  claim 28  wherein the scaling circuit comprises a switching circuit for switching between the different weights to select one weight for application at a first time and another weight for application at another time in dependence upon a content of the signal to be filtered. 
     
     
         31 . A circuit according to  claim 28  comprising a summer for summing an output of each of the plurality of taps. 
     
     
         32 . A circuit comprising:
 an input port for receiving a first signal, the first signal received at a receiver via a communication interface and from a remote location;   a plurality of taps, each tap comprising an input port for receiving a tap input signal, a plurality of weight input ports each for receiving a weight, and a scaling circuit for scaling an applied weighting based on the received weights to scale the tap signal, the scaled tap signal for modifying the first signal.   
     
     
         33 . A circuit according to  claim 32  wherein the scaling circuit comprises a switching circuit for switching between the different weights to select one weight for application at a first time and another weight for application at another time within a same signal to be filtered. 
     
     
         34 . A circuit according to  claim 32  wherein the scaling circuit comprises a switching circuit for switching between the different weights to select one weight for application at a first time and another weight for application at another time in dependence upon a content of the signal to be filtered. 
     
     
         35 . A circuit according to  claim 32  comprising a summer for summing an output of each of the plurality of taps. 
     
     
         36 . A method comprising
 providing a receiver for receiving a signal transmitted across an optical fibre and for providing an electrical first signal;   using a filter, filtering the first signal with a non-linear filter to provide compensation to the first signal for distortion in the signal when transmitted resulting from driving a transmitter at a transmit end, wherein an output signal from the filter better approximates an ideal transmit signal for an intended modulation.   
     
     
         37 . A method comprising:
 manufacturing a circuit comprising:
 an input port for receiving a first signal; 
 a plurality of taps, each tap comprising an input port for receiving a tap input signal, a plurality of input ports each for receiving a weight, and a scaling circuit for scaling an applied weighting based on the received weights to scale the tap signal, the scaled tap signal for modifying the first signal; 
 testing the circuit and determining each of the plurality of weights based on testing thereof; and 
 setting each of the plurality of weights based on a result of the testing thereof and fixing each of the plurality of weights. 
   
     
     
         38 . A circuit comprising:
 a non-linear FIR filter comprising a plurality of taps, each tap having multiple weights and a scaling circuit for scaling the multiple weights to affect a signal propagating within the tap for nonlinear filtering of a first signal.   
     
     
         39 . A circuit according to  claim 38  wherein the non-linear filter is implemented as an analogue component within an integrated circuit.