PIC divider jitter measurement

Setup

Use two TAPR/T2-mini boards with common low noise 20 MHz reference (Wenzel ULN). Use divide-by-24 PIC divider so output is 833 kHz. Measure performance of the two independent outputs as DUT and REF using TimePod 5330A. Look at PN and ADEV/MDEV/TDEV/MTIE. Select integrated "RMS Time Jitter", from 1 Hz to 100 kHz. Note that jitter of single T2-mini + picDIV is sqrt(2) of measured results.

The PIC code for minimum divider is two line loop. That's 3 instruction cycles, which is 12 clock cycles per toggle, which results in a divide by 24 square wave.

        movlw   0xFF
loop:   xorwf   GPIO,F
        goto    loop

Results indicate the jitter of a T2-mini and its 8-pin PIC 12F675 PIC divider is under 1 ps.

Plots

Baseline (instrumentation noise floor)

T2-mini schematic

TimeLab integrated jitter calculation, per decade

Send quetions/comments to tvb