Upsampling DAC Spur Cancellation Using DC Offset Control
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Solution Overview
Problem
In high-speed digital-analog conversion (DAC) applications, unwanted spurs often occur at specific frequency divides of the DAC output, particularly at power of two multiples, which can interfere with the frequency bands selected for upsampling DACs, leading to performance issues.
Innovation Solution
The introduction of a controllable constant signal or CW tones into the DAC input, either through a DC offset or additional modulation, allows for the cancellation or elimination of these unwanted spurs by adjusting the amplitude and phase to match the spur amplitude and phase, thereby improving DAC performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-speed digital-analog conversion is implemented, then conversion speed is improved, but unwanted spurs occur at power of two divides of the DAC output frequency
Solution Approach 1:
The patent applies the 'Blessing in disguise' principle by converting the harmful spurs into beneficial cancellation signals. Specifically, the system identifies spurs at power-of-two divides of the DAC output frequency and generates cancellation tones at these same frequencies. By adjusting the amplitude and phase of these cancellation tones to match the spurs, the harmful spurs are transformed into constructive interference patterns that eliminate the unwanted frequencies while preserving the desired output.
2Adaptability or versatility
If upsampling is used in DAC, then output frequency flexibility is improved, but frequency bands are constrained to multiples of divide frequency
Solution Approach 1:
The patent applies the 'Parameter changes' principle by dynamically adjusting the amplitude and phase parameters of cancellation tones based on the detected spur characteristics. The system modifies these parameters in real-time to match the spur amplitude and phase at power-of-two divide frequencies, enabling effective spur cancellation across different operating conditions while maintaining frequency band flexibility.
3Object-generated harmful factors
If controllable constant signal is added to cancel spurs, then spur amplitude is reduced, but signal complexity increases
Solution Approach 1:
The patent applies the 'Intermediary (Mediator)' principle by introducing cancellation tones as intermediary signals between the DAC output and the final output. These cancellation tones serve as mediators that interfere destructively with the unwanted spurs, reducing their amplitude. The cancellation tones are generated and adjusted through a control system that monitors the DAC output and modifies the cancellation signal parameters accordingly.
Data Source
AI summary
A device includes an upsampling digital-analog converter (DAC) and logic to add a DC offset to a signal input to the DAC, the logic adapted to set the DC signal to cancel a DAC output spur.