Joined: 13 November 2008
Location: GB
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Hi Everyone, My interest is in fast startup time. I noted in the thread 'modes of operation(MLX71122)' that the significant factors are crystal startup and data slicer capacitor charging time... but I would like to know if there is a startup speed advantage by loading IFFPRES with a value obtained from an earlier IF filter calibration (therefore presetting IFFTUNE on startup)? Can you please give an indication of the settling time for the auto IF frequency tuning and the typical tuning range from the nominal 2MHz IF frequency. Many thanks

Joined: 1 January 2005
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You have several possibilities. If you operated the IC by switching between standby and receive and do not remove the power from the IC, the last IFFPRES remains.

The crystal startup time is quite short because the dividers start operating before the reference oscillator reaches its full amplitude.

You can avoid the data slicer charging time by using the peak detectors.

Also, it is not necessary to make the data slicer capacitor so large that its voltage does not change during the data pulses. It needs to be only large enough so the longest data pulse is not shortened with weak signals. The same is true for the peak detector capacitors. Another trick is to add a silicon diode from pin 27 to pin 32 with the cathode on pin 32. This will charge up the data slicer capacitor when the receiver is turned on and will shorten the time required for the data to charge it.

The 2MHz IF can be adjusted over a wide range, but if it is to close to the limits of tuning, there will be no reserve for autotuning when the temperature changes.