[time-nuts] Measuring startup chirp

Murray Greenman murray at rakon.co.nz
Sun May 4 23:07:19 EDT 2008

Perhaps I should mention that we are trying to qualify a new oscillator
chip which we have designed. The foundry we used is a specialist at
oscillator design and testing, and they have reported noticing the chirp
in their test facility. Their test system is general purpose and so has
different conditions to the finished product.

Hence we need to check their measurements on the finished product, which
is a small ceramic TCXO, where we have bonded-out die and the correct
crystals. There are no capacitors, except for the compensation system
provided on the silicon. To make matters worse, we have to look at this
problem throughout the operating temperature range, -40 to +85 deg C.

Since we are intending to supply these parts to existing customers, it's
not practical to suggest to them that they do anything different to what
they did with previous compatible products. It is likely we don't have a
problem in practice, but without measuring, we won't know. Indeed, do we
have a chirp start problem with existing products?

Essentially we've discovered a hole in our measurement capability, and
it's enmbarrassing that the foundry can measure the problem (we believe
they use a fancy Agilent Phase Noise system and post process the data)
and we can't!

Murray Greenman ZL1BPU

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