Current Steering DAC for Monotonic LED Dimming
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Solution Overview
Problem
Existing LED dimming circuits face challenges in maintaining a monotonic relationship between the control input and the variably controlled current, which is crucial for consistent light output modulation.
Innovation Solution
A circuit comprising a current mirror with input and output transistors, control transistors, and a decoder circuit that receives a control signal to selectively actuate the transistors, ensuring a monotonically modulated current output by converting the control signal into actuation signals to manage the mirror currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a current mirror circuit is used to generate variable current for LED dimming, then light output modulation is achieved, but monotonic relationship between control input and output current cannot be ensured
Solution Approach 1:
The current mirror circuit is segmented into multiple independent current branches, each controlled by a separate control transistor. The decoder circuit divides the control signal into multiple discrete control lines, allowing independent activation of each branch. This segmentation ensures that current output increases monotonically with control signal magnitude, as each activated branch adds a fixed current increment.
Solution Approach 2:
The circuit employs dynamic control transistors that are selectively activated based on the control signal magnitude. The decoder dynamically converts the control signal into appropriate transistor activation patterns, enabling the current output to dynamically adjust in a monotonic fashion while maintaining the adaptability needed for various dimming levels.
2Measurement precision
If multiple control transistors are used to achieve monotonic current modulation, then current control precision is improved, but device complexity increases
Solution Approach 1:
The decoder circuit serves multiple functions: it receives the control signal, decodes it into multiple control lines, and simultaneously drives multiple control transistors. This multi-functionality reduces overall circuit complexity by consolidating control logic into a single universal component rather than requiring separate control circuits for each transistor.
Solution Approach 2:
The decoder circuit acts as an intermediary between the control signal and the multiple control transistors. It translates a single control signal into coordinated activation patterns for multiple transistors, simplifying the control architecture while maintaining precise current control through the monotonic activation sequence.
Data Source
AI summary
A current source circuit is configured to receive a reference current at the input circuit path of a current mirror circuit. The current mirror circuit mirrors the reference current and generates mirror currents at a number of output circuit paths. A corresponding number of control transistors are connected in series with the output circuit paths. Each control transistor is selectively actuated in response to a control signal. A decoder circuit is configured to receive a variable control signal and generate actuation signals in response thereto to selective actuate the control transistors to pass the mirror current to an output node. At the output node, the passed mirror currents are summed to generate a variable output current. The variable current is monotonically modulated in response to the variable control signal.