Hybrid Output Driver With Calibrated Swing and Current Emphasis
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Solution Overview
Problem
Designing output driver circuits that operate at high speeds (e.g., 12.5 Gb/s) while minimizing jitter, noise, layout area, circuit complexity, return loss, and power consumption, while improving emphasis variation accuracy is challenging due to the complexity of parameters involved.
Innovation Solution
A hybrid output driver circuit is developed, incorporating a voltage mode main driver with adjustable differential output voltage swing and a current mode emphasis driver. The resistance of adjustable resistors is controlled by modifying the number of resistors connected in parallel, with a calibration process determining the actual resistance to achieve the desired output voltage swing, allowing the current mode emphasis driver to source/sink currents based on the selected voltage swing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the output driver circuit operates at higher speeds (e.g., 12.5 Gb/s), then the operating speed is improved, but jitter and noise increase
Solution Approach 1:
The output driver circuit is divided into two separate functional components: a voltage mode main driver for high-speed operation and a current mode emphasis driver for signal conditioning. This segmentation allows each component to be optimized independently, enabling high-speed operation while maintaining signal quality and minimizing jitter and noise through specialized design of each segment.
2Manufacturing precision
If the differential output voltage swing is adjusted to improve emphasis variation accuracy, then the manufacturing precision is improved, but the circuit complexity increases
Solution Approach 1:
The circuit incorporates adjustable resistors that allow dynamic adjustment of the differential output voltage swing. This dynamic capability enables precise control of emphasis variation accuracy through resistor value selection, achieving high manufacturing precision without requiring complex fixed circuit topologies, thus managing circuit complexity effectively.
3Manufacturing precision
If more resistors are connected in parallel to adjust the resistance value, then the manufacturing precision is improved, but the layout area increases
Solution Approach 1:
Instead of using multiple discrete resistors connected in parallel to achieve precise resistance values, the invention changes the parameter approach by using adjustable resistors with continuously variable resistance. This allows precise resistance control for accurate emphasis variation without requiring multiple parallel resistor connections, thereby reducing the layout area while maintaining manufacturing precision.
4Device complexity
If the voltage mode main driver uses fixed output voltage swing, then the device complexity is reduced, but the adaptability decreases
Solution Approach 1:
The voltage mode main driver incorporates adjustable resistors that enable dynamic adjustment of the differential output voltage swing. This dynamic element provides adaptability to different operating conditions and signal requirements without significantly increasing the overall driver circuit complexity, as the adjustment mechanism integrates smoothly into the existing voltage mode driver architecture.
Data Source
AI summary
A hybrid output driver includes a voltage mode main driver having an adjustable differential output voltage swing, and a current mode emphasis driver. Differential output voltage swing is adjusted by controlling the resistance of a first adjustable resistor coupled to a first voltage supply terminal, and the resistance of a second adjustable resistor coupled to a second voltage supply terminal. Resistances of the first and second adjustable resistors are adjusted by modifying a number of resistors connected in parallel. A calibration process measures the actual resistance of a similar resistor, and uses this resistance measurement to determine the number of resistors to be connected in parallel to provide the desired resistance. The current mode emphasis driver sources/sinks currents to/from differential output terminals of the hybrid output driver in response to an emphasis signal. These currents are selected in view of the selected differential output voltage swing and selected emphasis level.