I2C Input Circuitry With Cascode Isolation for Propagation Delay
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Solution Overview
Problem
Inter-integrated circuit (I2C) input circuitry experiences timing variations due to parasitic capacitance on long conductors used for pull-up current routing, leading to excessive propagation delay.
Innovation Solution
Incorporating a cascode transistor to isolate the parasitic capacitance of the conductor connecting the pull-up current circuit and the input circuit, which eliminates timing dependence related to routing capacitance and improves timing performance by passing pull-up current to the input circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If long conductors are used for pull-up current routing to connect the master device and slave devices, then the communication range is extended, but parasitic capacitance increases causing excessive propagation delay
Solution Approach 1:
A cascode transistor is introduced as an intermediary component between the pull-up current circuit and the input circuit. This cascode transistor acts as a buffer that isolates the parasitic capacitance of the long conductor from the input circuit, allowing the conductor to be long for extended communication range while preventing the parasitic capacitance from causing excessive propagation delay.
2Device complexity
If the pull-up current circuit is directly connected to the input circuit, then the circuit structure is simple, but timing variation occurs due to parasitic capacitance on the conductor
Solution Approach 1:
The cascode transistor serves as an intermediary element that minimally increases circuit complexity while significantly improving timing performance. By placing the cascode transistor in the pull-up current path, it isolates the input circuit from the parasitic capacitance of the conductor, ensuring stable timing characteristics without requiring a complete redesign of the I2C interface.
3Adaptability or versatility
If the conductor connecting the pull-up current circuit and input circuit is made longer to accommodate more devices, then device connectivity is improved, but timing dependence on routing capacitance increases
Solution Approach 1:
The cascode transistor acts as a buffer that decouples the timing performance from the conductor length. This allows the I2C bus to accommodate more devices with longer conductors while maintaining consistent timing characteristics, as the cascode transistor isolates the input circuit from the increasing parasitic capacitance.
Solution Approach 2:
The pull-up current path is segmented into two parts: the first part includes the pull-up current circuit and cascode transistor, while the second part includes the input circuit. This segmentation isolates the parasitic capacitance of the long conductor to a specific segment, preventing it from affecting the overall timing performance of the I2C communication.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces propagation delay, achieving timing performance improvements by isolating parasitic capacitance effects, with maximum propagation delays reduced to less than 10 nanoseconds compared to over 185 nanoseconds without the cascode transistor.
Implementation Method 1
timing variations due to parasitic capacitance on long conductors used for pull-up current routing
Data Source
AI summary
Inter-integrated circuit input circuitry includes a pull-up current circuit and an input circuit. The input circuit includes an output inverter, an input inverter, and a pull-up circuit. The pull-up circuit is coupled to an input of the input inverter, and includes a pull-up transistor and a cascode transistor. The pull-up transistor is coupled to the input of the input inverter. The cascode transistor is coupled to the pull-up current circuit and the pull-up transistor, and configured to isolate the pull-up transistor from capacitance of a conductor coupled to the pull-up current circuit and the input circuit.