PMOS Pre-Driver Level Converter With Built-In HDMI De-Emphasis
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Solution Overview
Problem
Conventional high definition video interface (HDMI) transmission equipment faces limitations in bandwidth due to high input capacitance of NMOS differential pairs and reliance on higher power domains, necessitating a high-speed pre-driver and voltage level converter with built-in de-emphasis capabilities.
Innovation Solution
An all-p-type metal-oxide-silicon (PMOS) cross-coupled level converter with four PMOS transistors and two de-emphasis PMOS transistors is used to convert and de-emphasize differential inputs, enabling efficient voltage level conversion across power domains while maintaining low power consumption and high-speed data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an NMOS differential transistor pair is used as a driver to drive over 10 mA of current, then the drive current capability is improved, but the input capacitance becomes high which limits the bandwidth
Solution Approach 1:
The driver stage is segmented into two separate stages: a pre-driver stage using PMOS transistors for high-speed operation with low input capacitance, and a subsequent driver stage using NMOS transistors for high current drive capability. This segmentation allows each stage to optimize for its specific function without the trade-off present in a single NMOS differential pair.
2Power
If the conventional driver uses an open drain structure with higher power domain (e.g., 3.3V), then the drive strength is improved, but the power consumption increases and bandwidth is limited
Solution Approach 1:
A PMOS-based pre-driver stage acts as an intermediary between the low-voltage (1.0V) serializer output and the high-voltage (3.3V) driver stage. This intermediate stage performs voltage level conversion and provides high-speed driving with lower power consumption, enabling the subsequent NMOS driver to operate efficiently without directly handling the high-speed signal from the serializer.
3Speed
If a high-speed pre-driver with built-in de-emphasis is used, then the bandwidth is enhanced and falling-edge de-emphasis is achieved, but the device complexity increases
Solution Approach 1:
The de-emphasis function is merged into the pre-driver stage by incorporating de-emphasis taps that tap into the differential signal paths. This integration allows the pre-driver to simultaneously perform voltage level conversion, high-speed driving, and de-emphasis without requiring separate dedicated circuits for each function, thereby reducing overall device complexity while achieving enhanced bandwidth.
Data Source
AI summary
In an example, a high-speed pre-driver and voltage level converter with built-in de-emphasis for HDMI transmit applications is provided. An exemplary integrated circuit includes a serializer, a pre-driver coupled to receive a differential input from the serializer, and a driver. The pre-driver includes all-p-type metal-oxide-silicon (PMOS) cross-coupled level converter comprising four PMOS transistors and two de-emphasis PMOS transistors forming a de-emphasis tap coupled to the output of the cross-coupled level converter. The driver is coupled to the pre-driver output and is configured to receive a differential input from the pre-driver.