Slew-Rate Output Driver Circuit for EMI and Crossover Voltage Control
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Solution Overview
Problem
In USB driver circuits, achieving controlled rise/fall times and transition time ratios while minimizing electromagnetic interference (EMI) and supply noise is challenging due to variations in initial conditions of capacitive feedback, leading to imprecise output crossover voltage control.
Innovation Solution
A slew-rate controlled driver circuit design utilizing pairs of auxiliary transistors and capacitors to manage rising and falling output slopes, with current generators and cascoded outputs to maintain constant current flow and reduce dependence on power supply voltage, ensuring controlled transition times and crossover voltage ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive feedback is used to control output crossover voltage, then the differential output crossover voltage range can be controlled, but the initial conditions of capacitive feedback on each clock cycle are not well controlled leading to imprecise voltage control
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitors to a known voltage level before each switching cycle. The control circuit ensures that capacitors C1 and C2 are charged to the output voltage level before the main switches Q1 and Q2 operate, eliminating uncertainty about initial conditions and enabling precise crossover voltage control.
Solution Approach 2:
The patent implements feedback by continuously monitoring the output voltage and using this information to control the charging of the capacitors and the switching of the main devices. The control circuit adjusts the capacitor charging based on the actual output voltage, ensuring precise and stable crossover voltage control despite variations in initial conditions.
2Productivity
If transition time is reduced to improve signal speed, then productivity increases, but electromagnetic interference and supply noise increase
Solution Approach 1:
The patent applies dynamics by using actively controlled switching with adjustable transition times. Instead of fixed mechanical switches, the invention uses controllable switches (Q1, Q2) whose transition characteristics can be optimized. The dynamic control allows achieving fast switching while managing EMI through controlled rise/fall times and optional snubber circuits.
Solution Approach 2:
The patent introduces intermediary elements including snubber circuits (RC networks) and controlled transition circuits between the switching devices and the load. These intermediaries smooth out the switching transitions, reducing electromagnetic interference and supply noise while maintaining acceptable transition speeds for USB communication.
3Reliability
If transition time ratio (rise-time over fall-time) is well controlled, then signal integrity improves, but device complexity increases due to additional control circuits
Solution Approach 1:
The patent applies asymmetry by allowing different transition times for rising and falling edges through independent control of the charging and discharging paths of the capacitors. The circuit can be configured with different resistor values or switching characteristics for each direction, enabling optimized rise-time and fall-time control for USB signal integrity requirements.
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 effectively reduces EMI and supply noise by maintaining precise control over transition times and crossover voltage ranges, improving the ratio of rise-time to fall-time and ensuring stable output signals between opposing driver circuits.
Implementation Method 1
at least one first main capacitance being connected between said first main gate and said first main drain; said at least one first main capacitance is configured to control rising output slope
Implementation Method 2
at least one second main capacitance being connected between said second main gate and said second main drain; said at least one second main capacitance is configured to control falling output slope
Data Source
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AI summary
The present invention concerns a slew-rate controlled driver circuit (100) for an integrated circuit having an input node (101) and an output node (102). Said slew-rate controlled driver circuit (100) comprising at least one main driver (110) configured to be connected to at least one current generator (160). Said at least one main driver (110) including at least one pair of first auxiliary driver's transistors (103), at least one first main capacitance (120) configured to reduce electromagnetic interferences, at least one first main driver transistor (130) connected to said at least one first main capacitance (120) and at least one pair of second auxiliary driver's transistors (107), at least one second main capacitance (140), and at least one second auxiliary driver transistor (150) connected to said at least one second main capacitance (140).