Voltage-Mode Differential Driver With Programmable Skew Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current-mode differential output drivers face issues such as delay skew, increased power consumption, and challenges in achieving accurate pre-emphasis at high speeds due to high impedance and parasitic resistance, which affect signal quality and eye-diagram openings in high-speed applications.
Innovation Solution
A programmable high-speed voltage-mode differential driver design with variable-impedance driver arms, independent delay programming, and dedicated on-chip termination circuitry to manage output impedance, pre-emphasis, and common mode voltage, reducing power consumption and improving signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If current-mode output driver is used, then output voltage is determined by current sources, but power consumption increases and delay skew occurs
Solution Approach 1:
The patent transitions from current-mode to voltage-mode operation, fundamentally changing the operating parameter of the driver. This allows independent control of output voltage and impedance, reducing power consumption while maintaining signal quality through separate programming of voltage swing and delay parameters
Solution Approach 2:
The patent introduces programmable delay elements that allow dynamic adjustment of signal timing. Each differential arm can be independently programmed to compensate for skew, enabling the system to adapt to varying timing requirements and maintain optimal signal quality across different operating conditions
2Measurement precision
If high impedance current sources are used, then output voltage is controlled, but parasitic resistance affects signal quality and eye-diagram openings
Solution Approach 1:
The patent changes from high-impedance current sources to low-impedance voltage sources with separate impedance control. This allows the output stage to drive capacitive loads more effectively, reducing the impact of parasitic resistance on signal quality and eye-diagram openings while maintaining precise voltage control
Solution Approach 2:
The patent introduces dedicated on-chip termination circuitry as an intermediary between the voltage-mode driver and the output. This termination network provides precise impedance matching and signal conditioning, compensating for parasitic effects and improving overall signal integrity
3Power
If current-mode driver with parallel output termination is used, then output impedance is determined, but 50% of current is shunted through termination
Solution Approach 1:
The patent changes the fundamental operation mode from current-mode to voltage-mode, allowing output impedance to be controlled through dedicated termination circuitry rather than being inherently high. This enables better power efficiency since current is only drawn when needed to charge/discharge output capacitance, while impedance control is achieved through separate termination networks
Solution Approach 2:
The patent separates the functions of voltage generation and impedance control into distinct circuits. The voltage-mode driver generates the output signal, while dedicated on-chip termination circuits provide impedance matching. This segmentation allows independent optimization of power efficiency and impedance control without the trade-off present in current-mode designs
Data Source
AI summary
A voltage-mode differential driver is disclosed. The differential driver includes two driver arms, each driver arm including a variable-impedance driver for driving a single-ended output signal. Each variable-impedance driver comprises multiple driver slices, where each driver slice includes a pre-driver circuit and a driver circuit. Advantageously, it has been determined that the disclosed voltage-mode driver design requires less power than conventional current-mode drivers. In one implementation, the disclosed voltage-mode driver design provides the capability of independently programming the delay of the two single-ended outputs so as to compensate for differential skew. Other embodiments and features are also disclosed.