Buffer Circuit Gate Dimensions Reduce EMI Noise in Semiconductor Drivers
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Solution Overview
Problem
Existing electro-optical panel drivers generate EMI noise due to high-frequency noise at the rising and falling edges of switch control signals, which decreases the reception sensitivity of portable devices like portable telephones.
Innovation Solution
A semiconductor device with a source circuit and control circuit that includes operational amplifiers, transmission gates, and a buffer circuit, where the number of transmission gates turned ON/OFF is optimized with respect to their gate width and length, and the buffer circuit's gate width and length, to reduce high-frequency noise and EMI noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a display driver uses operational amplifiers and transmission gates to drive source lines of an electro-optical panel, then the drive capability and voltage stability are improved, but high-frequency noise is generated at the rising and falling edges of switch control signals, causing EMI noise that decreases reception sensitivity of portable devices
Solution Approach 1:
The patent applies parameter changes by optimizing the gate width (W) and gate length (L) of MOSFETs in the transmission gates and buffer circuit. Specifically, it establishes a relationship between these geometric parameters: n×Wb×Lb≧K×(Wa/La), where n is the number of transmission gates, Wb and Lb are the gate dimensions of transmission gate MOSFETs, Wa and La are the gate dimensions of buffer circuit MOSFETs, and K is a constant. By adjusting these parameters, the rise/fall time of switch control signals is controlled to reduce high-frequency noise components while maintaining drive capability.
2Adaptability or versatility
If the number of transmission gates turned ON/OFF is increased to drive more source lines, then the coverage of the driver is improved, but the total switching noise and EMI radiation increase
Solution Approach 1:
The patent uses parameter changes to establish a quantitative relationship between the number of transmission gates (n) and their MOSFET dimensions (Wb, Lb) relative to the buffer circuit dimensions (Wa, La). This allows the system to scale the number of driven source lines while controlling the per-gate switching noise through optimized geometry, achieving both coverage and noise control.
Solution Approach 2:
The patent applies periodic action by using a buffer circuit to generate switch control signals that are periodically applied to multiple transmission gates. The buffer circuit outputs control signals in a controlled sequence, and by optimizing the MOSFET parameters, the periodic switching action is performed in a way that reduces cumulative noise while maintaining the ability to drive multiple source lines.
Data Source
AI summary
A semiconductor device includes a source circuit and a control circuit. The source circuit includes a plurality of operational amplifiers, a plurality of transmission gates, one end of each of the transmission gates being connected to a corresponding source line, and a buffer circuit that outputs a switch control signal. When the number of transmission gates that are turned ON/OFF using the buffer circuit is referred to as n, a gate width and a gate length of a MOSFET of each of the transmission gates are respectively referred to as Wb and Lb, a gate width and a gate length of a MOSFET of the buffer circuit are respectively referred to as Wa and La, and K indicates a constant, the relationship n×Wb×Lb≧K×(Wa/La) is satisfied.