Silicon Photonic Modulator Driver Circuit for High Swing at 25 Gbps
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Solution Overview
Problem
Conventional drive circuits for silicon photonic modulators face challenges in maintaining high data rates due to limited output voltage, which is insufficient to drive the modulators effectively, leading to increased production complexity and costs when multiple modulators or high-voltage MOS transistors are used.
Innovation Solution
A high-rate high-swing drive circuit is introduced, comprising a series of inverters, voltage bias modules, and an inductor, which amplifies and buffers the signal to increase the output voltage swing while ensuring high data rates, utilizing a combination of core and I/O MOS transistors with different power supplies to achieve higher withstanding voltages and extended bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-stage inverter is used to drive the silicon photonic modulator, then the circuit complexity is low, but the output drive voltage is only approximately 1 V which is insufficient to drive the modulator normally
Solution Approach 1:
The drive circuit is divided into multiple stages: a first inverter stage for signal inversion and a second inverter stage for voltage amplification. Each stage uses transistors with different gate lengths optimized for their specific function, allowing the circuit to achieve both low complexity and high reliability through functional segmentation.
Solution Approach 2:
The patent changes the gate length parameter of MOS transistors between stages. The first inverter uses transistors with a first gate length optimized for signal inversion, while the second inverter uses transistors with a second gate length (different from the first) optimized for voltage amplification. This parameter change enables the circuit to overcome voltage limitations without excessive complexity.
2Reliability
If multiple modulators or high-voltage MOS transistors are used to increase the drive voltage, then the modulator can be driven normally, but the production complexity and costs increase
Solution Approach 1:
Instead of using multiple modulators or high-voltage transistors throughout the entire circuit, the patent segments the inverter stages and applies different transistor specifications only where needed. The second inverter stage uses transistors with optimized gate lengths for high-voltage output, while the first stage uses standard transistors, thereby reducing production complexity and cost.
Solution Approach 2:
The patent optimizes the gate length parameter of MOS transistors in the second inverter stage to achieve higher output voltage swing. By changing this critical parameter only in the output stage rather than using high-voltage transistors throughout the entire circuit, the solution reduces manufacturing complexity and cost while maintaining reliable modulator driving capability.
3Speed
If the gate length of MOS transistor is reduced to increase the drive rate, then the drive rate increases, but the withstanding voltage of the transistor decreases
Solution Approach 1:
The patent segments the circuit into two inverter stages with different transistor gate lengths. The first inverter uses transistors with a first gate length optimized for high-speed operation, while the second inverter uses transistors with a second gate length (longer than the first) optimized for withstanding higher voltages. This segmentation allows each stage to be optimized for its specific function without compromise.
Solution Approach 2:
The patent changes the gate length parameter of MOS transistors between stages to resolve the speed-voltage trade-off. The first inverter uses transistors with a shorter gate length for high-speed switching, while the second inverter uses transistors with a longer gate length for higher voltage withstanding capability. This parameter change enables the circuit to achieve both high drive rate and sufficient withstanding voltage.
Data Source
AI summary
A high-rate high-swing drive circuit applied to a silicon photonic modulator is disclosed. The drive circuit is connected to a drive pre-stage circuit and a modulator load. The drive circuit includes at least one output circuit, and the output circuit includes: a first inverter, a first voltage bias module, a second inverter, a second voltage bias module, and an inductor. The drive circuit formed by using such a circuit connection increases an output swing of a drive while ensuring a high rate.