Open-Collector Modulator Driver With Gain Peaking for Wide Bandwidth
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Solution Overview
Problem
Prior art distributed amplifiers face limitations in output swing, excessive power consumption, and bandwidth due to large device size and parasitic capacitance, which restricts their performance in driving downstream modulators for high-speed optical transmission.
Innovation Solution
A distributed amplifier system with an impedance matching network, a DC block, a variable gain amplifier, and an emitter follower circuit to introduce gain peaking, along with a termination network and impedance matching elements, is used to optimize signal amplification and reduce parasitic capacitance, enabling efficient amplification of input signals for optic signal transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If large transistor devices are used to meet current requirements, then sufficient drive current is achieved, but parasitic capacitance increases and bandwidth is limited
Solution Approach 1:
The patent divides a single large transistor stage into multiple smaller transistor stages connected in a distributed configuration. Each stage contributes a portion of the total drive current while having reduced individual parasitic capacitance. The stages are coupled through transmission lines to achieve cumulative current output without proportionally cumulative capacitance penalty, thereby resolving the contradiction between drive current and bandwidth.
2Speed
If distributed amplifier architecture is used to reduce parasitic capacitance, then bandwidth is improved, but output swing is limited
Solution Approach 1:
The patent combines multiple distributed amplifier stages in parallel configuration where each stage contributes to both bandwidth and output swing. The transmission lines interconnecting the stages are designed to provide constructive signal addition, merging the output signals to achieve large voltage swing while maintaining the bandwidth benefits of distributed architecture through reduced individual stage capacitance.
3Speed
If distributed amplifier architecture is used to reduce parasitic capacitance, then bandwidth is improved, but power consumption becomes excessive
Solution Approach 1:
The patent segments the total required drive current across multiple smaller transistor stages, each consuming less power individually. The distributed configuration allows each stage to operate at lower current levels while achieving the same cumulative output through constructive signal addition via transmission lines, thereby reducing total power consumption compared to a single large stage while maintaining bandwidth performance.
Data Source
AI summary
A distributed amplifier system comprising an impedance matching network configured to match an input impedance to an output impedance of the signal source, and a DC block configured to block DC components in the input signal. A variable gain amplifier adjusts the gain applied to the input signal based on a gain control signal to generate a gain adjusted signal. An emitter follower circuit receives and processes the gain adjusted signal to introduce gain peaking to create a modified signal. A distributed amplifier receives and amplifies the modified signal from the emitter follower circuit, to create an amplified signal. The distributed amplifier includes a termination network and one or more impedance matching elements configured for gain shaping the amplified signal. The gain peaking introduced by the emitter follower circuit is controlled by a variable current source. The distributed amplifier may be an open collector distributed amplifier.