Constant-Current Resistor-Ladder DAC for Stable Supply Voltage
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Solution Overview
Problem
Digital to analog converters (DACs) in electronic devices cause oscillations in power supply voltage due to varying current draw, leading to malfunctions and artifacts in displays and other components.
Innovation Solution
A DAC maintains a stable total impedance between the supply voltage and ground by using a resistor ladder and switches to vary impedance before and after the output node, and employs thermometer coding to correlate digital data with switch operations, ensuring a constant current draw and reducing bit-to-bit skew.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a DAC varies current draw to generate different output voltages, then the DAC can produce the required analog output voltage range, but it causes oscillations in the power supply voltage
Solution Approach 1:
The patent changes the impedance parameters of the resistor ladder network dynamically. By adjusting the impedance values before and after the output node through switch operations, the system maintains a constant total impedance while varying the output voltage, thereby keeping current draw constant and preventing power supply oscillations
Solution Approach 2:
The patent implements dynamic switch operations within the resistor ladder network. The switches are controlled to change the impedance configuration in real-time based on the desired output voltage, allowing the system to adapt to different output requirements while maintaining constant current draw through coordinated switch states
2Device complexity
If a DAC uses traditional binary coding, then the device complexity is reduced, but bit-to-bit skew and output errors increase
Solution Approach 1:
The patent inverts the traditional binary coding approach by using thermometer coding. Instead of using a compact binary representation that requires complex timing synchronization, the system uses a linear sequential coding scheme where each bit directly corresponds to a specific switch or resistor element, eliminating bit-to-bit skew issues through the inherent sequential structure
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
This approach generates analog outputs less susceptible to errors and maintains a uniform current draw, minimizing power supply voltage variations and improving display performance.
Implementation Method 1
the DAC may include a resistor ladder to vary the output voltage by changing the impedance before and/or after (e.g., with respect to current flow) an output node to the power supply and ground, respectively
Implementation Method 2
switches (e.g., transistors) may be used to connect or disconnect a supply voltage (e.g., VDD) at locations in the resistor ladder before the output node and to connect or disconnect a ground (e.g., VSS) at locations in the resistor ladder after the output node
Implementation Method 3
Digital to analog converters (DACs) to convert digitally coded data (e.g., coded via binary code, grey-code, thermometer code, etc.) to a corresponding analog output voltage
Data Source
AI summary
An electronic device may include a digital to analog converter receiving digital signals and outputting analog signals based on the received digital signals. The electronic device may also include a power source to supply current to the digital to analog converter. The digital to analog converter may include a first resistor ladder section to electrically couple an output node of the digital to analog converter to the power source via a first number of resistors in series. The digital to analog converter may also include a second resistor ladder section to electrically couple the output node to a reference voltage via a second number of resistors in series. The sum of the first number of resistors in series and the second number of resistors in series may be the same for each of the different analog signals.