Post Go back to editing

VCO calibration for HMC7044

Category: Hardware
Product Number: HMC7044

We have a system where one 7044 on each PCB provides the clock and SYSREF signals for the 4 ADCs. The system consists of 20 of these PCBs with 320 receive channels. At room temperature, the system simultaneously acquires signals under the action of SYNC and performs phase correction, so that the phase of the signal received by the 320 channels is consistent with that of the reference channel. When the ambient temperature rises to 50 degrees Celsius, the phase consistency of the 320 channels is verified by using the phase correction factor calculated at room temperature, and it is found that a small number of channels have a phase difference of about 20 degrees from the reference channel.
According to the description of VCO calibration in the D version of the 7044's datasheet:

1.We read the value of 0x008C register and look at the capacitor bank calculated by the autotune algorithm. We found that when the temperature increased, the register value read from part of the 7044 increased by 1 compared to room temperature, and the PCBs with a phase difference of 20 degrees were the register value changed.

2.Keeping the ambient temperature unchanged (50 degrees Celsius), re-energizing after power-off, and testing again found that the 7044 with the previous register value changed returned to the value at room temperature, while some did not recover, and the new 7044 register value also changed.

Therefore, our experimental results show that at different temperatures, the auto-tuning algorithm will calculate different capacitance banks, which leads to a change in the clock phase of the 7044 output with the change of register value, so that the phase difference between the phase of the signal collected by the ADC and the reference signal after correction occurs.


I wonder if our conclusions are correct and if so, how to avoid this, as our products need to work properly at different temperatures and cannot tolerate such large phase differences.

Thank you so much for helping。

By the way, there is a similar question in the forum with the topic:

HMC7044 Phase Difference Compensation Issue

Parents
  • Hi Dainan,

    Your conclusions are correct. HMC7044 or any other PLL/VCO products with autocalibration can select different capacitor bank/bias levels. This depends on the temperature, supply levels, part-2-part variation, etc.

    The best way to overcome this problem is by using manual VCO calibration. 

    I recommend creating a lookup table for capacitor bank values of each HMC7044 after calibration of the system. Then, on each power-up, you can use the manual calibration feature described on page 32 of the HMC7044B datasheet. 
    HMC7044B (Rev.0) (analog.com)

    Thanks,

    Emrecan

  • Dear Emrecan:

    First of all, thank you for your reply to me.


    The VCO frequency of my system is constant and does not change throughout the operation. But the operating temperature range of the system is very wide, if I build a look-up table, do I need to measure the auto-calibrated capacitance bank (i.e., read the value of the 008C register) for each 7044 over the entire operating temperature range, and then manually adjust the 00B2 register in real time according to the current operating temperature while working? According to our testing, not every 7044's 008C register value will be changed over the entire operating temperature range

  • Hi Dainan, 

    All the capacitor banks have sufficient bandwidth to support lock-and-leave operation.

    Therefore, a capacitor value that is auto-selected under normal operating conditions can be used across all operating conditions.

    Below, I’ve outlined the manual calibration procedure for multiple systems.

    Assume there are 3 different HMC7044s in the system. First, run the auto-calibration under normal operating conditions. After completing the system-level calibration, read the capacitor bank values for each HMC7044. These values may vary. For example, let’s say we obtain the following values for the three HMC7044s:

    • System A: Capacitor bank 17
    • System B: Capacitor bank 18
    • System C: Capacitor bank 16

    Next, create a lookup table with these values.

    Finally, during system initialization, you can apply these values by following the manual calibration procedures. This means that when the system powers up, the specified values will be set for each HMC7044. After that, the part will use the same capacitor bank for all conditions, eliminating phase shift issues caused by different bank selections.

    Important Note: These capacitor bank values are not expected to be identical between different parts

    Thanks,
    Emrecan

  • Thank you so much.
    I think I get what you mean, and I'm going to test it as you describe.
    Thank you for your help again.

Reply Children
No Data