On 12/04/14 21:23, [email protected] wrote:
Magnus,
You are very much on the track that I was thinking. I belive you are
absolutly correct
in that a 90 degree phase shift would be ideal.
I did a bit more digging last night, and it turns out that an XOR phase
comparator
looking at the tank voltage and drive voltage may be ideal, as you
have suggested here. My main concern was that I plan to adjust the pulse
width of the push-pull the drive circuit to
adjust the power into the tank circuit. (Actually the drive will be
full bridge, transformer
coupled to the tank). That change in pulse width is where I was stuck,
mentall. However since
I'm in the 10Khz to 100Khz range and am generating the push-pull PWM
digitally, I can
just generate a second output at the same frequency and phase (or even
different phase)
than the drive signal to compare to the tank voltage. As you say
"away you go with a phase
detector"!
I propose to sample the voltage rather than just using a XOR-gate (and a
limiter in front of it to square things up). Thing is, the voltage from
your LC tank is very analogue, so make use of this fact.
I would put a PI-loop (one op-amp, two resistors and a cap) in there.
As for frequency, your actual drive-oscillator can run at 4 times the
rate and then use a frequency divider to provide the phases. This can
provide you with in-phase and quadrature signals. Look at Tayloe
detector in a search engine near you. The driven frequency will remain
in your range, but you now have a quadrature signal to compare with.
Cheers,
Magnus
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