Memory Output Buffer Pre-Driver Timing for SSN and Ringing Control
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Solution Overview
Problem
Existing output buffer designs face challenges in reducing simultaneous switching noise (SSN) due to high slew rates, which lead to short-circuit current and noise issues, requiring a better method for slew rate control to balance speed and noise manipulation.
Innovation Solution
The output buffer design incorporates a pre-driver with a series connection of PMOS and NMOS transistors, along with a pre-driver circuit that controls the slew rate by varying current sources to maintain constant drive strength, reducing switching noise across varying PTV conditions and loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high slew rate is used in output buffer, then fast processing speed is achieved, but simultaneous switching noise and short-circuit current increase
Solution Approach 1:
The pre-driver circuit proactively controls the gate voltages of PMOS and NMOS transistors before simultaneous switching occurs. By preemptively adjusting the drive strengths and timing of transistor activation, the circuit prevents excessive short-circuit current and noise generation at the output stage, while still maintaining fast processing speed.
Solution Approach 2:
The pre-driver dynamically adjusts the drive strength parameters of PMOS and NMOS transistors based on operating conditions. By varying gate voltages and current sources in the pre-driver, the circuit optimizes the slew rate to achieve fast switching while controlling noise and short-circuit current through parameter modulation.
2Object-generated harmful factors
If slew rate control is implemented to reduce noise, then simultaneous switching noise decreases, but data skew increases
Solution Approach 1:
The pre-driver employs dynamic control of transistor drive strengths rather than fixed slew rate limiting. By adaptively adjusting gate voltages and timing based on real-time operating conditions, the circuit maintains optimal balance between noise reduction and timing synchronization, preventing excessive data skew while controlling simultaneous switching noise.
Solution Approach 2:
The pre-driver circuit incorporates feedback mechanisms to monitor and adjust the switching behavior of output transistors. By sensing the state of PMOS and NMOS transistors and dynamically modifying drive signals, the circuit maintains proper timing relationships and minimizes data skew while achieving noise reduction through controlled slew rate.
Data Source
AI summary
A controlling output buffer slew rate method and an output buffer circuit for a memory device is provided. The output buffer include an output stage formed by a PMOS transistor and a NMOS transistor electrically connected in series, a pre-driver for respectively controlling each gate terminal of the PMOS transistor and the NMOS transistor in order to bring these transistors to the turning-on threshold, a first wire, for transmitting a pull-up signal, coupled between the output stage and the pre-driver, and a second wire, for transmitting a pull-down signal, coupled between the output stage and the pre-driver. After a DATA signal transition (logic state is changed from “H” to “L” or “L” from to “H”), the PMOS or NMOS transistor is turned off first, and then the NMOS or PMOS transistor is turned on due to the time difference between the pull-up signal and the pull-down signal.