Current DAC Spike Cancellation in Sigma-Delta Modulators
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Solution Overview
Problem
Sigma-delta modulators in analog-to-digital converters introduce errors due to current spikes from switched current sources, leading to noise and inter-symbol interference, which existing technologies have not effectively addressed.
Innovation Solution
Incorporating compensating capacitors and a driving circuit with an amplifier to null the current charging the capacitance associated with the current sources, thereby reducing current spikes and noise in the sigma-delta modulator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If switched current sources are used in the IDAC, then the digital-to-analog conversion function is achieved, but current spikes are generated that cause noise and inter-symbol interference
Solution Approach 1:
The patent captures the harmful current spikes generated by switched current sources and redirects them to charge compensating capacitors. By doing so, the harmful spikes are converted into useful charging current for the capacitors, which then discharge to provide compensating current that cancels the harmful effects of the original spikes on the output signal.
2Object-generated harmful factors
If compensating capacitors are added to reduce current spikes, then noise and inter-symbol interference are reduced, but device complexity increases
Solution Approach 1:
The compensating capacitors serve multiple functions: they capture harmful current spikes, store the captured current, and discharge to provide compensating current that cancels spike effects. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity while achieving noise reduction.
3Measurement precision
If the amplifier bandwidth is increased to match the sampling frequency, then the signal-to-noise ratio is improved, but power consumption increases
Solution Approach 1:
The patent adjusts the amplifier's bandwidth parameter to be approximately equal to the sampling frequency rather than making it significantly wider. This optimized parameter setting achieves the necessary signal-to-noise ratio improvement while avoiding the excessive power consumption that would result from a much wider bandwidth amplifier.
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
The solution significantly improves the signal-to-noise plus distortion ratio by approximately 8 dB, effectively reducing conversion errors and inter-symbol interference.
Implementation Method 1
The switching of the current sources can generate current spikes on the output of the IDAC. These current spikes can contribute to noise and inter-symbol interference in a sigma-delta analog-to-digital converter in some cases. Compensating capacitors may be connected to the current sources and driven with signals to reduce the current spikes.
Data Source
Figure 1~2
Figure 3A~3D
Figure 4A~4B
AI summary
Apparatus and methods for reducing noise and distortion in current digital-to-analog converters (IDACs) are described. Compensating capacitors may be connected to current sources in an IDAC. The compensating capacitors may be driven with signals derived from the output of the IDAC to cancel transient current spikes that would otherwise occur on the output of the IDAC.