VIC-5: will the phase-locked loop find this cell's resonance?
With these chokes and this cell, where is the resonance — and can this PLL reach it, hold it, and build the rise inside each gate?
- f₀
- Resonant frequency, Hz
- Δ
- Distance from VCO centre, Hz
- L
- Loop inductance, mH
- C
- Cell capacitance, nF
- x
- VCO centre frequency, kHz
LaTeX
f₀ = \frac{1}{2\pi \sqrt{L \cdot C}} \qquad Δ = \left| f₀ - x \right|
Method
- Add the chokes, find the resonance and the Q — the same first steps as the VIC simulation.
- Work out the PLL from its parts: natural frequency, damping, lock range, hold range, lock time.
- Compare the resonance to the VCO centre. Within the lock range, the loop snaps to it; within the hold range but outside the lock range, it pulls in after slipping cycles, which takes longer; outside the hold range, the VCO cannot be driven far enough and there is no lock.
- Count the cycles of resonance each gate admits, and ask how much of the resonant rise they build — the build-up calculation.
Assumptions
- Every assumption of every step. In particular the PLL is the linear second-order loop with a passive lag-lead filter, and the pickup coil gives the phase detector a clean signal at the resonant frequency.
- The VCO centre is where it sits at mid control voltage, and its gain is linear across the range. A 4046's tuning curve is not very linear.
- The pulse duty is fixed at 50 %, which is what the VCO's square-wave output gives before any pulse shaping.
- What is Meyer's here is the claim that the VIC-5 tracks the cell's resonance automatically. Loop theory says what it takes to do that; it does not say his circuit did.