Segmented Laser Driver Edge-Rate Control for Lower EMI
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Solution Overview
Problem
Existing optical driver circuits react quickly to enable signals, leading to sudden current changes that generate large electromagnetic interference (EMI) and fail to accommodate diverse pulse shapes required by optical receivers, necessitating control over edge rates of optical drive current.
Innovation Solution
The optical driver circuit incorporates a series of delay segments between drive cells and the enable control signal, using components like shift registers, buffers, or timers to introduce programmable time delays, allowing for step-wise current transitions and configurable edge rate control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the driver circuit reacts quickly to enable signals, then the response speed is improved, but electromagnetic interference increases
Solution Approach 1:
The driver circuit is divided into multiple drive cells (first drive cell, second drive cell, etc.) that are enabled sequentially through delay segments. This segmentation allows the total current change to be distributed over time, reducing EMI while maintaining overall response speed. Each drive cell contributes a portion of the total current, and their sequential activation creates a stepped current profile instead of a sudden jump.
Solution Approach 2:
Delay segments are introduced to create predetermined time delays between the enable signal and the activation of different drive cells. This preliminary timing arrangement ensures that current changes occur in a controlled sequence, reducing electromagnetic interference while still achieving fast overall response. The delay segments pre-establish the timing relationship needed to balance speed and EMI reduction.
2Device complexity
If the driver circuit uses a single enable signal, then the circuit complexity is reduced, but the ability to accommodate diverse pulse shapes is limited
Solution Approach 1:
The circuit uses configurable delay segments that can be adjusted to create different time delays for each drive cell. This dynamic configurability allows the same basic circuit structure to generate various pulse shapes (different rise times, fall times, and duty cycles) by simply changing delay parameters rather than redesigning the circuit. The delay segments can be programmed or tuned to match different optical receiver requirements.
3Manufacturing precision
If multiple drive cells are used with delay segments, then edge rate control is improved, but the device complexity increases
Solution Approach 1:
Multiple drive cells are merged in parallel, with each cell having an enable transistor and delay segment. The combined output of all drive cells drives the laser diode. This merging approach allows edge rate control through the coordinated operation of multiple simpler units rather than requiring a single complex circuit. The parallel structure enables independent control of each cell's contribution to the total current.
Data Source
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AI summary
An optical driver circuit is described herein having a plurality of drive cells and delay segments between their control signals resulting in the control of the rising and falling edge rates for an optical device driven by the optical driver circuit.