Low Common Mode Driver Using Replica Bias Circuit
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Solution Overview
Problem
Conventional low voltage differential signaling (LVDS) designs face challenges in real-time common mode level tracking and power efficiency due to longer settle times and high power consumption, especially when transitioning between low power and high speed modes, leading to limited responsiveness and silicon space inefficiencies.
Innovation Solution
The implementation of a replica bias circuit with a pre-driver and driver stage that includes regulator circuits to provide regulated power, allowing for high speed and low power signal transmissions by using a scale replica circuit for feedback voltage regulation and error amplification to control transistor operation, thereby optimizing output impedance and reducing power penalties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If back termination resistors are used for impedance matching in conventional LVDS designs, then differential reflection coefficients are improved, but common mode settle times increase and power consumption increases
Solution Approach 1:
The patent extracts and removes the back termination resistors from the conventional LVDS design. By eliminating these resistors, the design achieves faster common mode settle times without compromising differential reflection coefficients, as the resistors are the primary cause of the time delay and power consumption issues
Solution Approach 2:
The patent changes the electrical parameters of the output driver stage by using a differential current switch pair with a current source instead of resistive termination. This parameter change allows the circuit to maintain good differential reflection coefficients while achieving significantly faster common mode settling behavior
2Reliability
If back termination resistors are used for impedance matching, then differential reflection coefficients are improved, but power consumption increases by 50% to 100%
Solution Approach 1:
The patent removes the power-consuming back termination resistors from the design. By extracting these resistive elements, the system achieves the same differential reflection coefficient performance through an active current-based approach that consumes 50-100% less power than the resistive termination method
Solution Approach 2:
The patent substitutes the passive resistive termination mechanism with an active differential current switch pair controlled by a current source. This substitution replaces the power-hungry resistive system with a more efficient current-based system that maintains signal integrity while dramatically reducing power consumption
3Measurement precision
If common mode feedback filtering is used for real-time Vcm tracking, then common mode level control is improved, but responsiveness to mode changes deteriorates
Solution Approach 1:
The patent extracts and eliminates the common mode feedback filter from the design. By removing this filtering component, the system achieves instantaneous responsiveness to mode changes between LP and HS states, as the filter's inherent delay and smoothing effects are completely removed while maintaining adequate common mode control through the differential current switch architecture
Data Source
AI summary
Techniques to provide a replica bias circuit for a high speed and low voltage common mode driver. In an embodiment, a pre-driver is coupled to provide driver input voltages to the driver, which driver includes a set of circuit elements coupled to provide, based on the driver input voltages, an output signal of a differential output. In another embodiment, a regulator circuit is coupled to provide regulated power to the pre-driver and driver, where the regulator circuit includes a scale replica circuit having a replica of the first set of circuit elements.