Single-Ended CML Transmitter Biasing for Supply Noise Reduction
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Solution Overview
Problem
Single-ended current mode logic (CML) transmitters experience supply noise due to variable current draw when differential input signals toggle between polarities, leading to undesirable noise issues in electronic devices such as memory devices.
Innovation Solution
An enhanced single-ended CML transmitter is configured with two differential transistor pairs and load resistors, where the second bias current is adjusted based on operational mode or supply noise measurements to equalize current draw during polarity changes, thereby reducing supply noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single-ended CML transmitter is used to output data across a data link, then high signaling rate capability is achieved, but supply noise increases due to variable current draw when differential input signals toggle between polarities
Solution Approach 1:
The patent adjusts the bias current parameter dynamically based on the operational mode or supply noise measurements. By changing the bias current level, the system equalizes current draw during polarity changes, thereby reducing supply noise while maintaining high signaling rate capability
Solution Approach 2:
The system incorporates supply noise measurements to feedback control the bias current adjustment. The bias current is adjusted based on measured supply noise levels, creating a closed-loop system that actively reduces supply noise while preserving high-speed operation
2Object-generated harmful factors
If bias current is adjusted to equalize current draw during polarity changes, then supply noise is reduced, but device complexity increases due to additional control mechanisms
Solution Approach 1:
The system uses supply noise measurements taken by its own monitoring mechanisms to automatically adjust its bias current. This self-service approach reduces supply noise without requiring external complex control systems, as the transmitter autonomously regulates its own operating parameters
Data Source
AI summary
Methods, systems, and devices for mitigating supply noise in single-ended current mode logic (CML) transmitters are described. A first current source may generate a first bias current for a first differential transistor pair included in a CML transmitter, and a second current source may generate a second bias current for a second differential transistor pair. The first differential transistor pair may route the first bias current through either leg of the first differential transistor pair based on a polarity of an input signal and the second differential transistor pair may route the second bias current through either leg of the second differential transistor pair based on the polarity of the input signal. Based on a first polarity, the second bias current may be routed to a ground reference, and based on a second polarity, the second bias current may be routed through the first differential transistor pair to modify a load current internal to the CML transmitter.