RF Sampling DAC Dither Generation for Lower Spurious Emissions
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Solution Overview
Problem
Current RF sampling digital-to-analog converters (DACs) in wireless base stations face limitations due to current source mismatches, leading to high Integral Nonlinearity, which impacts spurious performance and spectral emissions, making it challenging to meet stringent spurious emission requirements.
Innovation Solution
A dither generator is introduced that produces a dither signal with a low peak-to-average power ratio, added to the RF DAC input, utilizing a noise generator, interpolation filter, and waveform storage circuit to improve spurious performance by reducing current source mismatch effects, and includes bandwidth scaling capabilities to simplify filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If current source mismatches are reduced to improve spurious performance, then spurious emissions are reduced, but device complexity increases due to additional dither generation circuitry
Solution Approach 1:
A dither signal is introduced as an intermediary element to mask the effects of current source mismatches. The dither generator inserts a low-level noise signal into the DAC input, which randomizes quantization errors and reduces spurious emissions by spreading spectral energy, thereby improving spurious performance without requiring precise current source matching
Solution Approach 2:
The invention changes the statistical parameters of the input signal by adding a dither component with specific characteristics (low peak-to-average power ratio). This parameter change transforms the quantization error from a deterministic function of current source mismatches into a randomized process, effectively reducing spurious emissions while maintaining acceptable device complexity
2Object-generated harmful factors
If dither signal amplitude is increased to reduce quantization errors, then spurious performance improves, but dynamic range is consumed
Solution Approach 1:
Instead of using full-scale dither signals that would consume significant dynamic range, the invention applies partial dithering with optimized amplitude levels. The dither signal is designed to have just sufficient amplitude to effectively randomize quantization errors and reduce spurious emissions, avoiding excessive dither that would waste dynamic range. The optimization balances dither amplitude against available dynamic range to achieve spurious performance improvement with minimal dynamic range consumption
Data Source
AI summary
A circuit includes a noise generator and a delay element. The output of the noise generator couples to the input of the delay element. The output of the delay element is coupled to a first input of a logic circuit, and the output of the noise generator is coupled to a second input of the logic circuit. The output of the logic circuit is coupled to a first control input of a waveform storage circuit. The waveform storage circuit is configured to produce a first digital waveform on its output responsive to a first logic state on the output of the logic circuit and to produce a second digital waveform on its output responsive to a second logic state on the output of the logic circuit. A sequencer has a sequencer output coupled to the second control input of the waveform storage circuit.