AC-Coupled HDMI Signal Transmission with DC Level Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The HDMI specification's reliance on DC coupling limits the use of high-speed serial driving circuits in HDMI transmitting modules due to voltage withstand requirements, making it difficult to employ large-scale integrated circuits with low voltage characteristics.
Innovation Solution
The implementation of an AC-coupled signal transmission system that compensates differential signal waveforms to maintain a constant DC component level, allowing for the use of large-scale integrated circuits with higher speed and larger scale integration, even when the ratio of logic 1 to logic 0 in the bit serial signal is not 5:5.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC coupling is used between the HDMI transmitting module and receiving module, then voltage characteristics corresponding to pulled up voltage (3.3V) can be maintained, but large-scale integrated circuits with low withstand voltage characteristics cannot be utilized
Solution Approach 1:
An AC coupling capacitor is introduced as an intermediary component between the transmitting module and receiving module. This capacitor blocks DC voltage while allowing AC signal transmission, thereby isolating the low-voltage integrated circuit from the 3.3V pulled-up voltage at the receiver side. The capacitor serves as a mediator that enables voltage level incompatibility between transmitter and receiver.
2Adaptability or versatility
If AC coupling is used to enable low voltage integrated circuits, then integrated circuit scalability is improved, but differential signal DC component levels may vary causing detection errors
Solution Approach 1:
The transmitting module performs preliminary adjustment of the differential signal waveform before transmission. By proactively controlling the DC component levels of the differential signals to maintain a predetermined relationship (e.g., equalizing DC components or maintaining constant differential DC level), the system prevents detection errors from occurring at the receiver side, rather than attempting to correct them afterward.
Solution Approach 2:
The system monitors the actual DC component levels of the differential signals and adjusts the transmission waveform accordingly. By implementing feedback control, the transmitting module can dynamically compensate for variations in signal levels caused by AC coupling, ensuring that the received signals maintain appropriate voltage characteristics for reliable detection.
3Device complexity
If signal transmission is performed without AC coupling, then circuit design is simpler, but voltage withstand requirements limit the use of advanced integrated circuits
Solution Approach 1:
The system changes the voltage parameter characteristics by using AC coupling to block DC voltage levels. This parameter change allows the transmitting module to operate at low voltages suitable for modern integrated circuits while the receiving module can tolerate the 3.3V pulled-up voltage, effectively decoupling the voltage requirements of the two modules and enabling the use of advanced low-voltage ICs.
Data Source
AI summary
According to one embodiment, a signal transmission apparatus being AC-coupled with a receiving apparatus through a digital transmission line includes a transmitting module configured to transmit a differential signal based on an encoded bit serial input signal such that a low frequency component of the differential signal to be transmitted is maintained at a constant level when the differential signal based on the encoded bit serial input signal is transmitted to the digital transmission line where the encoded bit serial input signal includes a ratio of the number of logic 1 to the number of logic 0 which is different from 5:5.