Dual-Mode PAM/NRZ Transmitter Driver With Reconfigurable Impedance
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Solution Overview
Problem
Existing transmitters face challenges in efficiently operating at multiple data rates while maintaining impedance and avoiding inefficiencies such as increased area and performance degradation due to power gating of least significant bit (LSB) data paths.
Innovation Solution
A dual-mode transmitter design with a first and second driver, where resistors from the LSB driver are coupled to the MSB driver in the NRZ mode to maintain impedance without increasing effective pad capacitance, and both drivers are used in PAM3 mode to process MSB and LSB bits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If power gating is applied to LSB data paths at lower data rates, then power consumption is reduced, but impedance decreases and performance degrades
Solution Approach 1:
The transmitter dynamically reconfigures the impedance network based on operating mode. In PAM mode, the full impedance network is active. In NRZ mode, switches reconfigure the network to maintain proper impedance even with LSB paths power-gated, allowing adaptive optimization for each mode without permanent degradation
Solution Approach 2:
The impedance characteristics of the transmitter are changed by reconfiguring the resistor network through switches. By changing the effective resistance values in the impedance network based on operating mode, the system maintains optimal impedance matching for both PAM and NRZ modes while enabling power gating
2Use of energy by moving object
If LSB driver is power gated in NRZ mode, then power savings are achieved, but effective pad capacitance increases
Solution Approach 1:
The harmful effect of increased pad capacitance is extracted and isolated by providing a separate impedance maintenance path through the reconfigurable resistor network. This allows the LSB driver to be power-gated without its capacitance loading the output, as the impedance network compensates for the removed driver contribution
3Reliability
If additional resistors are added to maintain impedance, then impedance matching is improved, but area increases
Solution Approach 1:
The resistor network serves multiple functions: it provides impedance matching in PAM mode, maintains impedance in NRZ mode when LSB is power-gated, and can be reconfigured through switches to adapt to different operating conditions. This multi-functionality eliminates the need for separate impedance matching circuits for each mode, reducing total area
Solution Approach 2:
The impedance maintenance function is merged with the existing driver structure by integrating the reconfigurable resistor network into the driver output stage. This combines impedance matching with the driver functionality, eliminating the need for separate impedance matching components and reducing overall transmitter area
Data Source
AI summary
Embodiments herein relate to a transmitter which can operate in a non-return-to-zero (NRZ) mode or a pulse amplitude modulation (PAM) mode with three or more levels. The transmitter includes a first driver which processes most significant bits and a second driver which processes least significant bits, in the PAM3 mode. In the NRZ mode, the second driver is turned off but resistances in the second driver are used to optimize impedance in the first driver. Switches can be turned on to couple in resistors in the first driver with resistors in the second driver, for pairs of driver slices. The switches are turned off in the PAM3 mode.