Distributed CML Level Shifter for Large Voltage Swing Drivers
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Solution Overview
Problem
Current-mode logic (CML) drivers face limitations in achieving large output current-mode voltage levels when the load is not directly DC-coupled to a power supply, particularly in applications requiring large voltage swings, due to headroom limitations from the driver's transistors.
Innovation Solution
The implementation of a distributed current-mode level shifter coupled with a distributed amplifier, utilizing multiple current source segments and inductive components, which increases output voltage amplitude without increasing power consumption by eliminating headroom limitations and matching impedance with termination resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional CML driver is used with non-DC-coupled load, then the circuit structure is simple, but the output voltage level is limited due to headroom limitations from transistors
Solution Approach 1:
The driver is divided into multiple functional segments: input transistors for signal reception, current source segments with inductive components for voltage level transformation, and distributed amplifier stages. Each segment performs a specific function, allowing the overall system to achieve high output voltage levels while maintaining manageable complexity through modular design.
Solution Approach 2:
Inductive components are introduced as intermediary elements between the input transistors and the output stage. These inductors act as mediators that enable voltage level transformation without being directly coupled to DC power supplies, thereby overcoming headroom limitations while maintaining circuit functionality.
2Power
If the output voltage level is increased to achieve large voltage swings, then the voltage swing capability is improved, but the power consumption increases
Solution Approach 1:
The circuit transforms the operating parameters by using inductive components to store and release energy, enabling large voltage swings without proportional increases in continuous power consumption. The inductors convert current-mode signals to voltage-mode signals with elevated levels, achieving high voltage swing capability while maintaining efficient power utilization through periodic energy storage and release cycles.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows for increased output voltage levels while maintaining high bandwidth and reducing power consumption, effectively addressing the limitations of existing CML drivers in applications with large voltage swings.
Implementation Method 1
Each current source segment includes a first inductive component coupled between the first current terminal at a second node and the first resistor, and each current source segment also includes a third transistor having fifth and sixth current terminals, the fifth current terminal being coupled to the second power supply node, and the first inductive component is connected to the sixth current terminal
Implementation Method 2
The distributed current-mode level shifter includes a first plurality of inductors coupled in series between the first termination resistor and the distributed amplifier and a first plurality of capacitive devices. Each capacitive device is coupled to a power supply node and to a node interconnecting two of the series-coupled inductors
Data Source
AI summary
A driver circuit includes a first termination resistor and a distributed amplifier comprising a plurality of pairs of input transistors and comprising inductors coupled between each pair of input transistors. The driver circuit also includes a distributed current-mode level shifter coupled to the first termination resistor. The distributed current-mode level shifter includes a first plurality of inductors coupled in series between the first termination resistor and the distributed amplifier and a first plurality of capacitive devices. Each capacitive device is coupled to a power supply node and to a node interconnecting two of the series-coupled inductors.