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Read back filter calibration in ADF7021-N

Question asked by AkeHallberg on May 17, 2011
Latest reply on May 23, 2011 by bkearns

It is possible to read back filter calibration result. In datasheet it is showed that the upper most 8 bits should be all zeros and the filter calibration is placed in the 8 lower bits. In my application the bit number 9 (DB8) is one. Should this bit be treated as zero?

The calibration result are 8 bits and if I want to save this result and store it in "IF_FILTER_ADJUST" it should be calculated as "FILTER_CAL_READBACK" - 128. This calculation has the effect that the upper most bit (DB7) is inverted and nothing else. Then this result should be stored in "IF_FILTER_ADJUST" that occupies only 6 bits. How should I treat the 8 bit result so it can take place in only 6 bits?

My read back is 0x78 and after the subtraction the result is 0xF8. If I truncate it to 6 bits or if I right shift two times the result is a very big negative number and the receiver will not work good at all after I reprogram the register 5 with this value for "IF_FILTER_ADJUST"!

If I program register 5 with "IF_FILTER_ADJUST" set to all zeros then the receiver will work OK.



Ake Hallberg