Display Source Driver Output Circuit Using Segmented Low-Voltage Switches
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Solution Overview
Problem
Conventional LCD source drivers require switches with high voltage tolerance to achieve a 10V voltage swing, leading to a large chip area due to the need for significant voltage tolerance, which is inefficient.
Innovation Solution
An output circuit utilizing low voltage switches, including operation amplifiers, transmission gates, and switches with specific control signals, allows for a voltage swing of +5V to 0V and -5V, reducing the chip area by using switches with only a 5V tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If switches with high voltage tolerance are used to achieve a 10V voltage swing, then the voltage swing requirement is met, but the chip area becomes large
Solution Approach 1:
The output circuit is divided into two independent paths: a first path for positive polarity output and a second path for negative polarity output. Each path uses switches with only 5V tolerance instead of requiring a single path with 10V tolerance switches. This segmentation allows the use of smaller, lower-voltage-tolerance switches while still achieving the required 10V total voltage swing through the combined operation of both paths.
2Area of stationary object
If switches with 5V tolerance are used, then the chip area is reduced, but the voltage swing capability is limited
Solution Approach 1:
The first output path and second output path are merged into a single output node. The first path generates positive voltage swings (0V to +5V) while the second path generates negative voltage swings (-5V to 0V). By combining these two paths at the output node, the circuit achieves a total voltage swing of 10V (from -5V to +5V) using only 5V tolerance switches, thus reducing chip area while maintaining voltage swing capability.
3Device complexity
If a single output path is used, then the circuit structure is simple, but high voltage tolerance switches are required
Solution Approach 1:
The single output path is segmented into two independent output paths: a first output path with a first switch for positive polarity and a second output path with a second switch for negative polarity. Each path can use switches with only 5V tolerance instead of requiring a single path with 10V tolerance switches. This segmentation maintains circuit simplicity while reducing the voltage tolerance requirement for individual switches.
Solution Approach 2:
A polarity determination circuit acts as an intermediary to control which output path is active based on the polarity of the input signal. The polarity determination circuit receives the input signal and generates control signals to enable the appropriate output path (first or second path) based on whether the input is positive or negative polarity, thus mediating between the input signal and the output switches.
Data Source
AI summary
An output circuit whose outputting signals having large voltage swing by using switches with low voltage tolerance is provided. The output circuit includes: operation amplifiers, receiving positive input voltage and negative input voltages, respectively; transmission gates, passing output signals from the operation amplifiers, respectively; switch transistors, passing output signals from the transmission gates as an output signal of the output circuit, pulling up the output signal from one of the transmission gates, and pulling down the output signal from the other of the transmission gates.