CMOS PAM-N Serial Link Using Weighted NRZ Signal Combining
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Solution Overview
Problem
Current integrated circuits (ICs) face challenges in transmitting multi-level signaling, such as PAM-N, as CMOS inverters saturate signals to two discrete levels, making it difficult to generate, transmit, or buffer multi-level signals, and existing solutions like current mode logic introduce complexity and issues with signal communication between transmitters and receivers.
Innovation Solution
The method involves forming a multi-level PAM-N signal at the transmitter using CMOS-based components, where multiple NRZ input voltage signals are converted to current signals and combined into a PAM-N output signal using CMOS-inverter-based circuits, allowing for single transmission line communication without the need for recombination or realignment at the receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If CMOS inverters are used for signal transmission, then the circuit complexity is reduced and manufacturing is simplified, but the inverter saturates multi-level signals to two discrete levels, causing signal distortion and loss of information
Solution Approach 1:
The transmitter is divided into multiple parallel input converter circuits, each handling a portion of the multi-level signal. By segmenting the signal processing across multiple converters with different weighting factors, the system can represent multi-level signals as weighted sums of binary signals, allowing CMOS inverters to work in their comfortable binary domain while still transmitting multi-level information.
Solution Approach 2:
The invention changes the parameter representation of the signal by expressing multi-level signals as weighted combinations of binary signals. Each input converter circuit is assigned a specific weighting factor, and the binary outputs are combined arithmetically to reconstruct the multi-level signal at the receiver, transforming the signal representation to be compatible with CMOS binary operation.
2Adaptability or versatility
If current mode logic (CML) or multiple NRZ parallel paths are used to communicate multi-level signals, then the ability to transmit multi-level signals is improved, but the device complexity and issues with signal communication increase
Solution Approach 1:
The invention makes CMOS inverter circuits universal by enabling them to handle both binary and multi-level signals through the weighted combination approach. The same CMOS inverter building blocks can be used for NRZ signaling, and by adding the weighted combination layer, they can also handle PAM-N signaling, eliminating the need for separate CML circuits or multiple parallel paths.
Solution Approach 2:
The invention adds a dimensional transformation by converting multi-level signal transmission into a multi-dimensional binary signal space. Instead of transmitting one multi-level signal on a single line, the system transmits multiple binary signals in parallel that can be combined to reconstruct the multi-level signal, effectively adding the dimension of weighted combination to the transmission system.
3Productivity
If multi-level PAM signaling is implemented, then the data transmission rate is improved, but the signal becomes more susceptible to distortion and requires more complex receiver processing
Solution Approach 1:
The transmitter performs preliminary action by pre-computing the weighted combination of binary signals that will represent the multi-level signal. By encoding the multi-level signal as a weighted sum of binary signals at the transmitter, the receiver only needs to perform simple binary detection and arithmetic combination, avoiding complex multi-level detection and reducing susceptibility to distortion.
Data Source
AI summary
Methods, systems, and apparatus described herein make a multi-level PAM signal (PAM-N signal) at a transmitter using CMOS-based components. By forming the PAM-N signal at the transmitter, receivers do not have to recombine and/or realign multiple signals and only employs a single transmission line channel (or two transmission line channels in differential implementations) to convey the data stream to the receiver from the transmitter.