**Part Number:** LMX2594

Dear TI,

the issue if the LMX2594 has a noise floor of -236dBc/Hz has been raised once before. The answer from TI and the datasheet itself proving the -236dBc value is not clear though.

The noise floor value in question of -236dBc/Hz is proven only from the Figure 14 - "Calculation of PLL Noise Metrics" in the datasheet. However, the noise floor itself is not shown in the measurement trace in this Figure at all! What is shown is the 1/f noise and not the flat phase noise region. You may draw the red line as an indication of the flat region, but this red line without the measurement data trace is misleading.

Calculating the true noise floor of the part LMX2594 can be done from the several phase noise measurements in the datasheet, the eval board and other LMX2594-related gizmos (i.e. TIDA-01346, Multiple PLL Combination Reference Design).

Calculating the PLL noise floors and therefore FOMs from the Figures 3, 4, 5, 6, 7 and 9 (hopefully TI used Wenzel 100MHz OCXO for these figures) using the 20LOG(N) and 10LOG(Fpd) reveals the realistic value of **-228dBc/Hz**, **8dB** worse than the specified value of -236dBc:

Fig. 3: Flat noise floor at 100kHz offset: -107.5dBc/Hz - 20*LOG(15000/200) - 10*LOG(200e6) = **-228.0dBc/Hz**!

Please clarify the issue or the possible miscalculation.

Thanks and best regards,

Leon