DDS background - Table of contents

Coherent | Alias | Skip | Hiccap | PT-spurs | AQ-spurs

DDS background

DDS: Direct Digital Synthesis = point(memory location)-skipping at constant f_c update(clock) - rate
[ vs. traditional PPC (point-per-clock) synthesis at variable clock-rate ]

Finite memory requirement: coherent sampling
    Discrete-time vs. continuous-time sinusoid
Nyquist-zones: images and aliasing
    Point sampling, frequency conversion (folding)
Point(memory location)-skipping: temporal "scrambling"
    Reversible permutation of samples, and ModT (re)plot
Jittered sampling: phase hiccap
    Limited memory size, constant interpolation (virtual table)
Phase Truncation (PT) spurs: overlapped modulation structure
    Where is the truncation "noise"?
        // Tuning condition where there is
        - no PT-distortion
        - just one spur (worst case)
        - spur pairs //
Amplitude Quantization (AQ) spurs: overlapped harmonic structure
     Where is the quantization "noise"?
        //Tuning condition where there is
        - no AQ-distortion (only loss, scaling factor): f = f_c/4
        - coincident spurs (massive overlap): short numerical period
        - close-in or "cross-over" spurs (fine offset): narrow band
        - a "sea" of fine spaced spurs: long period //
        *
NRZ (non return to zero) mode DAC
    sin(x)/x spectral envelope (amplitude rolloff)
SINC interpolation
    Exact interpolation with periodic samples (finite sum)
FFT artifacts: resolution (selectivity) or detection (sensitivity)?
    Spectral leakage (bin splatter), picket-fence (scallop loss) and windowing

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