Follower Output Buffer for Adaptive Transmission Line Impedance
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Solution Overview
Problem
Existing output buffers, such as CMOS output buffers, face challenges in maintaining impedance matching with transmission lines, leading to signal integrity issues like ringing, crosstalk, and inter-symbol interference due to variable impedance during signal switching, and they often transmit supply noise directly onto the transmission line without attenuation.
Innovation Solution
An output buffer comprising a follower circuit with an NMOS transistor and a PMOS transistor, where the drain terminal of the NMOS transistor is coupled to a local supply voltage and the drain terminal of the PMOS transistor is coupled to a local ground voltage, effectively adapting the output impedance to match the transmission line impedance and reducing supply noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a CMOS output buffer is sized to have the desired output impedance, then the output impedance matches the transmission line impedance at a specific voltage, but the impedance becomes variable during signal switching, resulting in impedance mismatch
Solution Approach 1:
The patent applies the Dynamics principle by making the output impedance adaptive rather than fixed. The follower circuit dynamically adjusts the output impedance to match the transmission line impedance during signal switching transitions. The circuit transitions from a static CMOS buffer with fixed impedance to a dynamic system that continuously adapts its impedance characteristics based on the switching state, resolving the contradiction between achieving precise impedance matching and maintaining adaptability during transitions.
2Object-generated harmful factors
If the output edge slope is slowed down to limit current peak slope and reduce internal noise, then supply noise is reduced, but inter-symbol interference increases due to longer transition time
Solution Approach 1:
The patent applies the Intermediary principle by introducing a follower circuit as an intermediate stage between the CMOS buffer and the transmission line. This follower circuit acts as a mediator that decouples the direct connection, allowing the CMOS buffer to drive the follower while the follower provides impedance matching and noise filtering to the transmission line. The intermediary follower circuit reduces supply noise coupling while maintaining fast edge slopes, resolving the contradiction between noise reduction and signal integrity.
3Manufacturing precision
If the CMOS transistor resistance is equal to the transmission line impedance, then impedance matching is achieved, but supply noise is transmitted directly onto the transmission line without attenuation
Solution Approach 1:
The follower circuit serves as an intermediary that breaks the direct noise transmission path while maintaining impedance matching. The follower's high input impedance prevents loading effects on the CMOS buffer, and its low output impedance provides proper matching to the transmission line. This intermediary structure allows the circuit to achieve impedance matching without directly coupling supply noise to the transmission line, as the follower isolates the noisy supply from the output.
Solution Approach 2:
The patent applies the Local quality principle by creating different impedance characteristics at different stages of the buffer circuit. The CMOS buffer stage operates with high impedance to minimize loading, while the follower stage provides low output impedance for optimal transmission line matching. This local differentiation of impedance properties allows each stage to operate optimally - the CMOS buffer generates the signal with minimal loading, and the follower provides impedance matching and noise isolation at the output interface.
Data Source
AI summary
Embodiments include but are not limited to apparatuses and systems including an output buffer including an input terminal for receiving an input signal, an output terminal for outputting an output signal, and a follower circuit coupling the input terminal and the output terminal, the follower circuit including at least one set of an NMOS transistor and a PMOS transistor, a drain terminal of the NMOS transistor coupled to a local supply voltage, and a drain terminal of the PMOS transistor coupled to a local ground voltage. Other embodiments may be described and claimed.