DAC Input Timing With Pseudo-Data Feedthrough Cancellation
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Solution Overview
Problem
Digital to analog conversion (DAC) circuits face issues with digital signal interference due to minute capacitance between digital inputs and analog outputs, causing unwanted frequency content in analog signals, even at low signal levels.
Innovation Solution
A method is introduced where a cancellation data stream is generated by adding pseudo-data outside the setup and hold time window of the data stream, maintaining data presence within the window, and applying this stream to the DAC to shift energy to a spectrum that can be filtered out, thereby minimizing digital feedthrough.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional DAC operation is used with standard data timing, then the DAC operates simply and efficiently, but digital signal interference couples through capacitance to corrupt the analog output
Solution Approach 1:
The patent applies preliminary action by modifying the data stream in advance before it reaches the DAC. Pseudo-data values are inserted into time slots outside the setup and hold windows ahead of time, preparing the data stream to cancel digital feedthrough interference at its source rather than filtering it from the analog output later
Solution Approach 2:
The patent converts the harmful digital feedthrough effect into a benefit by using the same capacitance coupling mechanism to our advantage. By inserting pseudo-data values that are inversely correlated with the actual data, the harmful capacitance coupling now transfers inverted signals that cancel the interference, turning the previously harmful effect into a useful cancellation mechanism
2Object-affected harmful factors
If pseudo-data is added outside the time window to create cancellation data stream, then digital feedthrough is reduced, but the data processing becomes more complex
Solution Approach 1:
The patent applies periodic action by systematically inserting pseudo-data values at regular periodic intervals corresponding to the clock cycle. The pseudo-data is placed in specific time slots that repeat each clock period, creating a periodic cancellation pattern that consistently counteracts the digital feedthrough interference across all clock cycles
Solution Approach 2:
The patent applies parameter changes by modifying the temporal distribution of data values in the data stream. By changing when data values are present (inserting pseudo-data in non-critical time slots outside setup and hold windows) and altering the amplitude relationship (using inverted values for cancellation), the system reduces interference while maintaining functional correctness
3Productivity
If data is present only during setup and hold time window, then the DAC timing is efficient, but frequency content couples through to corrupt analog waveform
Solution Approach 1:
The patent applies segmentation by dividing the clock cycle into distinct functional segments: the setup and hold time window where actual data values are present for proper latching, and the remaining time slots where pseudo-data values are inserted for interference cancellation. This segmentation allows each portion of the data stream to serve its specific function without interfering with the other
Data Source
AI summary
A method for operating a DAC to minimize digital feedthrough includes inputting a clock signal to a DAC clock input, the clock signal having a periodic series of trigger events, wherein input data must be present for a time window between a setup time before a trigger event and a hold time after the trigger event; generating an input data stream, the input data stream having data that is present for the time window; altering the input data stream into a cancellation data stream wherein the data presence is maintained but pseudo-data outside of the time window is added; and applying the cancellation data stream to a DAC data input resulting in an analog signal output.