PLL on crank angle sensor input

[Stuart Woolford]

On Tue, 04 Mar 1997 12:41:52 -0800, Steven Arnold wrote:

>I am in the process of designing an microcontroller ignition system, and
>was wondering - 
>
>how common is it to use a PLL on the crank angle sensor input?
>does any one have a typical circuit design for this part of an efi
>system?
>

there would be several problems.

1 - due to the settling time and cnostantly changing RPM, there would exist an offset
error in the PLL output due to the (nescessary) finite transition time.

2 - PLL's have a tradeoff between transition time, bandwidth, and stability, etc, which make
them poor for jobs with a wide dynamic range and varying rates of change.

3 - you would have trouble if the PLL missed or gained extra signal, giving large short-term
changes.

basically, the best method is to use a second order or higher software system to allow for
rate-of-change, etc, to interpolate additional accuracy, this can work very well.

for example, toyota use a 6 tooth per engine revolution cam position system in some of their
engines, yet get very accurate ignition timing, as they use higher order software approximations
to gain additional resolution.

basically, a simple PLL is just not up to the job.
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Stuart Woolford, stuartw at kcbbs.gen.nz

               >>>>In VI Where Available<<<<
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