Adjustable Video DAC Termination for Cable-Sensed Power Saving
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Solution Overview
Problem
Current multimedia System on a Chip (SOC) designs require significant power to drive 75 Ohm loads for video output, and existing jack sense circuits waste power by enabling video DACs even when cables are not connected to a video display, lacking efficient detection of load impedance and type.
Innovation Solution
The proposed solution includes a jack sense module that uses a processing module to determine the number of connected cables and enable only necessary video DACs, employing a gated termination mechanism to adjust current sources and impedance based on cable connections, and an impedance comparator to ensure proper load detection, reducing power consumption and optimizing video output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If 75 Ohm termination is used for video output, then impedance matching is achieved, but power consumption increases
Solution Approach 1:
The patent implements dynamic termination control where the 75 Ohm termination is only activated when a cable is detected at the video output jack. The system transitions between high-impedance state (no cable) and 75 Ohm terminated state (cable present), allowing impedance matching only when needed rather than continuously, thus reducing power consumption while maintaining signal integrity when required
2Difficulty of detecting and measuring
If jack sense circuit with pull up resistor and mechanical switch is used, then cable connection detection is achieved, but device complexity increases
Solution Approach 1:
The patent combines the jack sense functionality with the video output driver circuitry by integrating the pull-up resistor and detection logic into the existing video DAC output stage. The same output driver that drives the video signal also performs the impedance transformation and termination control, eliminating the need for separate sense circuits and reducing overall device complexity
Solution Approach 2:
The video output driver is designed to perform multiple functions: driving the video signal, detecting cable presence through integrated sense circuitry, and providing dynamic termination. This multi-functional approach consolidates what would traditionally require separate components into a single integrated block, reducing device complexity
3Adaptability or versatility
If video DAC is enabled continuously, then video output is always available, but power consumption increases
Solution Approach 1:
The patent implements feedback-based control where the output driver continuously monitors the impedance at its output terminal. When a cable is detected (impedance change from high to 75 Ohm), the system feedbacks this information to enable the video DAC and activate termination. When no cable is present, the DAC remains disabled, reducing power consumption while maintaining readiness to output video when needed
Data Source
AI summary
A digital to analog converter (DAC) includes at least one digital to analog conversion module and a gated termination. The at least one digital to analog conversion module is coupled to convert at least one bit of a digital signal into an analog signal. The gated termination is coupled to an analog output of the at least one digital to analog conversion module to provide a first termination when a termination selection signal is in a first state and to provide a second termination when the termination selection signal is in a second state.