DDS Mixed-Signal Circuit Using Pseudo-Random Phase Dithering
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Solution Overview
Problem
In mixed-signal integrated circuits, spurious signals are injected into analog circuitry due to digital transitions, causing noise and temperature variations, which affect the fidelity of carrier wave signals and require reducing data-dependent digital activity while maintaining acceptable digital resource costs.
Innovation Solution
A digital circuit with a noise generator producing pseudo-random noise signals is integrated into direct digital synthesis circuits to randomize phase generator inputs, reducing data dependency and toggle activity, and a compensation circuit is used to maintain equivalent input-output behavior with reduced digital resource usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct digital synthesis is used to generate carrier wave signals, then signal generation flexibility and precision are improved, but spurious signals are injected into analog circuitry due to digital transitions
Solution Approach 1:
A pseudo-random noise sequence is introduced as an intermediary element to randomize the timing of digital transitions in the DDS circuit. This mediation technique disperses the spurious signal energy across a broader frequency spectrum, reducing peak spurious levels while maintaining the precision of carrier wave generation. The noise sequence acts as a buffer between the digital control logic and the analog output stage.
Solution Approach 2:
The invention changes the temporal distribution parameter of digital transitions by applying pseudo-random dithering to the phase accumulator input. Instead of uniform or regular transition patterns, the transitions are randomized in time, which transforms the spectral characteristics of spurious signals from concentrated peaks to distributed low-level noise, thereby improving signal fidelity.
2Measurement precision
If digital transitions are reduced to minimize spurious signals, then spurious-free dynamic range is improved, but data-dependent power dissipation and temperature variations in analog circuitry increase
Solution Approach 1:
The invention employs periodic pseudo-random noise sequences with carefully selected periods and patterns to regularize the distribution of digital switching activity. This periodic dithering ensures that power dissipation and heat generation are distributed uniformly over time, preventing localized temperature spikes while maintaining low spurious signal levels through the randomization effect.
3Measurement precision
If data-dependent digital activity is reduced to minimize spurious signals, then signal fidelity is improved, but digital resource costs increase
Solution Approach 1:
Instead of completely eliminating data-dependent digital activity, the invention applies partial randomization through pseudo-noise dithering at optimized levels. This partial action approach achieves sufficient spurious signal reduction for high-fidelity applications while avoiding the excessive digital resources that would be required for complete activity elimination or more complex mitigation architectures.
Data Source
AI summary
The present invention is related to a digital circuit for use in a mixed-signal circuit. The digital circuit comprises:a first circuit for direct digital synthesis comprising a first phase generator (PG1) arranged for being fed with a phase generator input signal, a first phase-to-amplitude converter (PAC1) arranged for being fed with a phase from the first phase generator and for generating a first carrier wave output, and first signal combining means (R1) for combining the first carrier wave output with a first input signal,a noise generator (NG) arranged for generating a pseudo-random noise signal,combining means (S) for combining the pseudo-random noise signal and the phase generator input signal such that the phase generator input signal to the first phase generator (PG1) is randomised,a second circuit for direct digital synthesis comprising a second phase generator (PG2) arranged for being fed with the pseudo-random noise signal, a second phase-to-amplitude converter (PAC2) arranged for being fed with a phase from the second phase generator and for generating a second carrier wave output, and second signal combining means (R2) for combining the second carrier wave output with a second input signal, whereby the second carrier wave output combined with the second input signal is comprised in the first input signal.