Transmitter Driver High Frequency Booster for PAM4 Signal Swing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
PAM4 signaling faces challenges in maintaining sufficient signal swing and bandwidth at high speeds, particularly above 56 Gbps, due to decreased signal swing and bandwidth limitations, which are exacerbated by low power supply and low breakdown voltage requirements, and existing solutions like high efficiency voltage mode drivers and FIR filters are either insufficient or power-intensive.
Innovation Solution
A transmitter driver circuit is enhanced with a continuous time high-pass filter response using an AC-coupled feed-forward path and a high frequency booster, which injects additional current specifically for high frequency signals, thereby boosting voltage without affecting low frequencies, and includes control switches to adapt bandwidth for varying data rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PAM4 signaling is used for high speed transmission, then data rate is improved, but signal swing is reduced by 1/3 compared to NRZ signaling
Solution Approach 1:
The driver is segmented into two independent voltage mode drivers (first and second) operating in parallel, each handling differential signals. This segmentation allows independent optimization of each driver stage while maintaining overall high data rate capability, and the parallel structure provides current boosting capability to compensate for reduced signal swing in PAM4 signaling
Solution Approach 2:
The patent combines multiple voltage mode drivers with a current source in a hybrid configuration. The current source provides supplementary current that merges with the output of the voltage mode drivers, effectively boosting the output swing without compromising the high data rate capability. This merging of voltage-mode and current-mode operation resolves the contradiction between high speed and sufficient signal swing
2Speed
If bandwidth is increased to support high data rates above 56 Gbps, then data transmission capability is improved, but vertical eye opening in the eye diagram is degraded
Solution Approach 1:
The patent employs dynamic control switches that can enable or disable the secondary data path and high frequency booster based on operating conditions. This dynamic adjustment allows the driver to adapt its bandwidth and boost characteristics to maintain optimal eye opening at different data rates, particularly preserving vertical eye opening when operating above 56 Gbps by selectively activating high frequency compensation paths
3Strength
If a FIR filter is used to provide voltage boost, then voltage swing is increased, but power consumption and physical area increase significantly
Solution Approach 1:
The patent extracts only the essential high frequency boosting function from a full FIR filter implementation. By using a simplified high frequency booster with selective frequency enhancement rather than a complete FIR filter, the design achieves necessary voltage swing improvement while dramatically reducing power consumption and physical area requirements. The extraction focuses only on the critical high frequency compensation needed for PAM4 signaling
4Adaptability or versatility
If control switches are added to adapt bandwidth for different data rates, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent implements dynamic control switches that can enable or disable the secondary data path and high frequency booster based on operating conditions. This dynamic adjustment allows the driver to adapt its bandwidth and boost characteristics to maintain optimal eye opening at different data rates, particularly preserving vertical eye opening when operating above 56 Gbps by selectively activating high frequency compensation paths
Solution Approach 2:
The control switches serve multiple functions: they enable bandwidth adaptation for different data rates, select between different operating modes (voltage-mode only or hybrid), and control the activation of the high frequency booster. This multi-functionality reduces the need for separate control circuits for each function, thereby limiting the increase in device complexity while achieving broad adaptability
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 effectively increases bandwidth and voltage swing for high frequency signals, improving communication quality and reducing power consumption by selectively enabling high frequency boost only when needed, resulting in quicker output response and reduced intersymbol interference.
Implementation Method 1
A continuous time high-pass filter response is added to the transmitter output, using an AC-coupled feed-forward path. The capacitor-coupled path causes the voltage at the current source to change, such that more current is injected to the output at data transmission.
Implementation Method 2
A continuous time high-pass filter response is added to the transmitter output, using an AC-coupled feed-forward path. This additional current helps to boost the voltage of high frequency signals, and has little or no effect on low frequency signals.
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A transmitter driver is disclosed. The transmitter driver includes first and second voltage mode drivers and a secondary data path. The secondary data path is connected in parallel with the first and second voltage mode drivers. A high frequency booster provides a high frequency path for boost current from the current source, to enable a high frequency voltage boost at the output ports.