Variable-Load Output Circuit for Balanced Rise and Fall Slew Rates
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Solution Overview
Problem
Existing CMOS output circuits face challenges in achieving balanced rise and fall slew rates due to difficulties in fine adjustment and increased circuit scale when using series-connected PMOS and NMOS transistors or parallel-connected transistors with stepwise drive power changes.
Innovation Solution
An output circuit with a signal output unit, a variable load circuit, and a switch circuit that controls electrical conduction and non-conduction between the signal output node and the load circuit, allowing independent adjustment of rise and fall slew rates by connecting or disconnecting the load circuit during signal transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If series-connected PMOS and NMOS transistors are used to control rise and fall slew rates, then the output circuit can produce balanced slopes, but fine adjustment is difficult and the circuit scale increases
Solution Approach 1:
The patent changes the parameter of load capacitance by connecting different sized capacitors to the output node during rise and fall transitions. This allows continuous adjustment of slew rates without increasing transistor count, resolving the contradiction between precision and circuit scale
Solution Approach 2:
The patent introduces capacitors as intermediary elements that mediate the slew rate control function. These capacitors work with simple switches to achieve fine adjustment of rise and fall slopes without requiring complex transistor arrangements
2Ease of operation
If parallel-connected transistors are used to change drive power, then the slew rates can be controlled, but the circuit scale increases and fine adjustment is difficult due to stepwise changes
Solution Approach 1:
The patent uses variable capacitance values to continuously adjust slew rates, replacing the stepwise transistor switching approach. This enables fine-grained control of rise and fall slopes without increasing circuit scale or requiring multiple parallel transistors
3Power
If multiple transistors are connected in parallel to control slew rates, then the drive power can be adjusted, but the circuit scale increases
Solution Approach 1:
The patent adjusts drive power by changing capacitance values rather than multiplying transistor instances. This allows continuous power adjustment for rise and fall transitions without increasing circuit scale, as the same capacitor can be reconfigured for different functions
Data Source
AI summary
The present invention is aimed at providing an output circuit that is of relatively small scale and may perform adjustment to make the output-signal rise slew rate and the fall slew rate equal to each other. An output circuit includes a signal output unit configured to produce at a signal output node a signal that makes transition between a first potential and a second potential, a load circuit having a variable load, and a first switch circuit configured to select one of electrical conduction and non-conduction between the signal output node and the load circuit.