Display Driver IC Clock Frequency Stabilization via Host Feedback
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Solution Overview
Problem
The frequency of the clock signal used by display driver ICs is sensitive to temperature variations, leading to electromagnetic interference (EMI) that affects other devices, such as touch screens and stylus pens, particularly in mobile devices with liquid crystal display (LCD) panels.
Innovation Solution
A display driver integrated circuit (DDI) and a host system that include a control signal generator, receiver, and controller to adjust the frequency of the operating clock signal based on a data transmission timing control signal, using a frequency calculation circuit to determine if the frequency is within a predetermined range and generating a frequency control signal to adjust the clock signal accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an RC oscillator is used to generate the clock signal for panel self-refresh, then the circuit structure is simple, but the frequency deviates due to temperature sensitivity causing EMI
Solution Approach 1:
The patent implements a feedback mechanism where the host receives the TE signal from the DDI, calculates its frequency, compares it with a reference frequency, and generates a frequency control signal back to the DDI. This closed-loop feedback system automatically compensates for frequency deviations caused by temperature variations, resolving the contradiction between simple circuit structure and frequency stability.
Solution Approach 2:
The system uses the DDI's own TE signal as the measurement object for frequency detection, eliminating the need for separate reference clocks or crystal oscillators. The DDI essentially measures and corrects its own frequency deviations through the host's calculation and feedback, achieving self-service frequency stabilization.
2Reliability
If the clock signal frequency is stabilized using traditional methods, then frequency stability is improved, but the circuit structure becomes more complex requiring separate reference clocks and crystal oscillators
Solution Approach 1:
The patent eliminates the need for separate reference clocks and crystal oscillators by using the DDI's own TE signal as the measurement basis. The host calculates the frequency of the TE signal directly and generates feedback control signals, allowing the system to stabilize frequency without additional dedicated frequency reference components.
Solution Approach 2:
The host performs multiple functions: it receives display data, calculates the TE signal frequency, compares it with reference frequency, and generates frequency control signals. This multi-functional approach consolidates frequency stabilization functionality into existing components, avoiding the need for separate dedicated frequency reference circuits.
3Object-affected harmful factors
If the frequency of the operating clock signal is adjusted to compensate for temperature variation, then EMI is reduced, but additional frequency control mechanisms are required
Solution Approach 1:
The patent uses a feedback control mechanism where the host continuously monitors the TE signal frequency and adjusts the DDI's clock frequency accordingly. This automatic frequency adjustment compensates for temperature-induced deviations, reducing EMI while using only the existing TE signal transmission path for control.
Solution Approach 2:
The TE signal serves as an intermediary that carries frequency information from the DDI to the host. The host uses this signal to calculate frequency deviations and generate control signals, which are then transmitted back to the DDI to adjust the clock frequency, eliminating the need for separate frequency sensing and control circuits.
Data Source
AI summary
A display driver integrated circuit (DDI) for driving a display of image data on a display panel, an application processor (AP), a system including the DDI and the AP, and methods of operating the same are provided. The application processor includes: a controller configured to obtain a frequency of a data transmission timing control received from a display driver integrated circuit (DDI), and to generate, based on the obtained frequency, a frequency control signal for adjusting a frequency related to an operating clock signal for the DDI; a transmitter configured to transmit the generated frequency control signal to the DDI; and a frequency calculation circuit including: a detector configured to receive the data transmission timing control signal from the DDI, and a frequency calculator configured to calculate a frequency of the received data transmission timing control signal.