OK, here I'm stumped. Reciprocals. Analogue. What'm trying to do is measure a frequency and produce a voltage that is a linear representation of said frequency.
Now something like a frequency counter will measure how many cycles in one second (say) and display the result. Fine. But I wish to measure the frequency within a single cycle of input waveform. To do this you gate a much higher frequency with the input.
So a 1MHz clock gated at 1kHz will produce a count of 1000. At 2kHz a count of 500 and so on...this is the equivalent of 1/f, to get the true figure you need a division, a reciprocal. Now one could use a micro to do this either by calculation or a look-up table. But that I do not want to do.
Many years ago (about 20) I did produce an analogue circuit that did this. But I'll be jiggered if I can remember how.
Any suggestions?
Yours,
Banging head against wall, Bangkok.
I should add that there are analogue division/multiplication circuits around, National Semiconductor produced a number of application notes for these. But they were moderately complex and often required awkward thermistors for temperature compensation.
Whatever I devised decades ago was either a stroke of genius or fundamentally flawed. Probably the latter...