We found the unstable synth_lock voltage issue of HMC764LP6CE under high temp and failure ratio is around half on our board. The register setting and schematic is as attached. In sum, the failure situation is as below two.
1. The output frequency is fixed and LD_SDO is stable under normal temp (25C). While the temp goes up to 85C, the LD_SDO is unstable (synth lock is fail) even though the output frequency is fixed and stable. As attached is PCB No.12.
2. The output frequency and LD_SDO all are stable under high temp (85C). But, it is failure once the output frequency has been changed.As attached is PCB No.23.
Would you kind to have some recommendations or something been ignored ?