Calibrated Multi-Bit Transmitter for PAM-4 Linearity Control
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Solution Overview
Problem
Multi-bit data transmission is vulnerable to noise due to narrower signal level gaps, leading to degraded linearity and impedance variations in termination resistors, which affect signal quality.
Innovation Solution
A transmitter with a driver circuit that controls the turn-on impedance of pull-up and pull-down paths using control signals generated by an encoder and calibration circuit, ensuring even signal distribution and impedance matching for improved linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-level signals such as PAM-4 are used to transmit multi-bit data, then data transmission speed is improved, but the signal becomes vulnerable to noise due to narrower gaps between signal levels
Solution Approach 1:
The patent changes the impedance parameter of the pull-up path dynamically based on the control signal values. By adjusting the impedance of the pull-up path to be smaller when the control signal indicates a higher voltage level, the system compensates for the non-linear voltage distribution caused by the termination resistor's impedance variation, thereby maintaining more uniform voltage gaps between signal levels and improving noise resistance while preserving high-speed multi-bit transmission
2Productivity
If multi-bit data is transmitted using multi-level signals, then transmission efficiency is improved, but linearity of the transmitter is degraded due to impedance variations in termination resistors
Solution Approach 1:
The patent dynamically changes the impedance parameter of the pull-up path based on the control signal values. When the control signal indicates a higher voltage level, the pull-up path impedance is reduced, which compensates for the increased termination resistor impedance at higher voltage levels. This dynamic parameter adjustment maintains more uniform voltage distribution and improves transmitter linearity while preserving multi-bit transmission efficiency
Solution Approach 2:
The system uses the control signal values as feedback to adjust the pull-up path impedance. The encoder generates control signals that reflect the desired voltage levels, and these same control signals are used to modulate the pull-up path impedance, creating a feedback mechanism that compensates for non-linearities and improves overall system linearity
Data Source
AI summary
A transmitter includes a driver circuit configured to drive a channel connected to a first node by controlling a turn-on impedance of a pull-up path, a turn on impedance of a pull-down path, or both according to a plurality of control signals; an encoder configured to generate the plurality of control signals according to a multi-bit data and a calibration signal; and a calibration circuit configured to generate the calibration signal including calibration information corresponding to the plurality of control signals, wherein the encoder determines activation and magnitude of each of the plurality of control signals according to the multi-bit data and the calibration information.