Digital Bus Interface for Reliable DSI Signal Edge Detection
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Solution Overview
Problem
Existing interfaces for bidirectional communication, such as those using the DALI standard, are not suitable for protocols like DSI where the bus is idle at zero or low voltage, leading to unreliable detection of digital signals due to capacitive effects that interfere with the recognition of falling edges.
Innovation Solution
A digital bus interface with a transmission branch and a reception branch, where the reception branch has a current source that supplies energy to both branches, and an energy store that discharges via a resistor connected in series with the optocoupler, allowing for quick recognition of digital signal edges and compatibility with both DALI and DSI standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If capacitor C2 is used to store energy in the receiving branch, then the interface can operate with a common power source for both transmitting and receiving branches, but the falling edge of DSI signals cannot be reliably detected because the capacitor remains partially charged and bridges the Zener diode
Solution Approach 1:
The patent divides the energy storage function into two separate capacitors: capacitor C1 in the receiving branch and capacitor C2 in the transmitting branch. This segmentation allows each capacitor to be optimized for its specific function without interfering with the other, particularly enabling reliable detection of falling edges in DSI mode while maintaining operation in DALI mode
Solution Approach 2:
The patent extracts the energy storage capacitor C2 from the receiving branch and places it in the transmitting branch. This removal of the capacitive element from the signal detection path eliminates the interference that was preventing reliable detection of falling edges, while the transmitting branch still benefits from energy storage for driving the optocoupler
2Ease of operation
If the bus voltage drops to zero or low level for DSI signal transmission, then the interface can detect logical states, but the charged capacitor C2 continues to charge and prevents immediate detection of the first logic state
Solution Approach 1:
The patent configures capacitor C1 to charge quickly during the high level period (approximately 833 μs) in advance, so that when the voltage drops to low level, the capacitor is already charged and ready to immediately detect the falling edge without delay. This preliminary charging action ensures the first logic state is detected immediately
Solution Approach 2:
The patent introduces a resistor R6 in series with capacitor C1 that controls the charging current. This intermediary resistor allows the capacitor to charge quickly during the high level while limiting the current to prevent excessive power consumption, and ensures the capacitor can discharge quickly when the voltage drops, enabling immediate detection of the first logic state
3Power
If capacitor C2 is placed in the transmitting branch with the optocoupler, then the optocoupler can be driven with stored energy, but the edge time of transmitted digital bits becomes too long (greater than 25ms)
Solution Approach 1:
The patent changes the capacitance value of C2 to be smaller (1-6 μF) compared to C1 (1-6 μF but with different charging characteristics), and adjusts the series resistor R5 to create a charging circuit that provides high current during the bit transmission period. This parameter optimization allows the capacitor to discharge quickly through the optocoupler, achieving edge times less than 25 ms while still providing sufficient drive power
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
Enables reliable detection of digital signals, particularly the falling edge of DSI signals, and ensures immediate recognition even when the bus voltage is close to zero, improving edge steepness and signal integrity.
Implementation Method 1
an electrical energy storage device, e.g. one or more capacitors, is provided in the receiving branch, which is charged by the current source
Implementation Method 2
the transmitting branch has an optocoupler
Implementation Method 3
the Zener diode Z1, which would otherwise immediately interrupt the current flow in the optocoupler U2 of the receive branch
Data Source
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AI summary
The invention relates to a digital bus interface for an operating device for a lighting means comprising: a transmitting branch and a receiving branch, wherein the receiving branch has a current source (Q90, Q95, R90, R91), which can be fed from a bus that carries voltage in the idle state, wherein the current source supplies at least the transmitting branch with energy and the transmitting branch has an optocoupler (U91), wherein an electrical energy store (C95) is provided in the receiving branch, which electrical energy store is charged by the current source and discharges via a resistor (100) in series with the secondary side of the optocoupler (U91) of the transmitting branch.