HMC765 vs HMC767

Question

Hello there, 
 We are thinking in migrating a current design from HMC767 to avoid excesively low tning voltages to get 8GHz output frequency. Our idea is to use HMC765 instead but phase noise floor degradation seems to be expected. My questions are: 
 1. it is a real risk on locking HMC767 around such a low tuning voltage (around 1.1Volts to get 8GHz output frequency) or we can go on with original design based on that reference? 
 2. If move to HMC765, can we take the advantage of auxiliary DC circuitry coming from previous design: HMC976 and HMC860, instead of using those devices recommended at HMC765 datasheet: 3 units of LP5900-3_3V and 2 units of LP3878MR-ADJ (both VCO models seems to have similar current consumption) 
 3. That 4dB PN degradation from HMC765 higher PN floor is unavoidable to be suffered at 8GHz output (we are going to use PLL as integer with up to 100MHz FPD) 
 4. Any other recommendation to get the closest possible performance than that obtained previously with HMC767? 
 
 A lot of questions... Thanks in advance to help me finding the best possible design at a new frequency. 
 Best Regards

MRichardson · Accepted Answer

Hi, 
 You didn't mention your application or the loop BW you're using so the following is assuming that REF / PFD, Icp etc. must remain as they are. 
 
 1) I don't recommend attempting to use the HMC767 for an 8.0 GHz application. Over process & temperature at 8 GHz, Vtune could drop well below 1.1 Volts which will result in increased spurious in fractional mode due to the proximity to low rail, inability to lock depending on op amp characteristics (would need a rail-rail op amp like the ADA4084-1 or ADA4625). 
 2) Yes I would recommend you use the HMC976 and HMC860 LDO's used with the HMC767 as a minimum. Depending on the ampacity, spurious and isolation needs of your application you may be able to get away with a single HMC1060 (Using VR4 for the VCO and the remainder of outputs to isolate analog / digital and LS / CP circuits. The HMC1060 includes a PTAT circuit which compensates for voltage change over temp. 
 3) Not sure what the question is here. 
 
 4) The HMC834 would be a good option to consider if the VCO PN performance is acceptable (-100 dBc @ 100kHz at 8 GHz) 
 
 5) The ADF5356, particularly for an integer mode application might be considered. VCO PN is about -108 dBc @ 1 00kHz at 8 GHz). Like the HMC765 it does not include sweep functions so I'm guessing these aren't needed. Although the FOM is only about 1 dB better it has a few attractive features. The ADF5356 uses a passive loop which will eliminate the need for an op amp reducing cost and saving board space which means there's more room to improve the layout for better isolation potentially. It also offers multiple outputs which may be helpful. 
 
 5) The ADF5610 has a similar FOM as the HMC767 with similar VCO performance but it covers a total of 8 octaves. This part has the flexibility to work across multiple platforms both today and in the future which may provide some economy of scale. It too utilizes a passive loop filter and only loses about 1 dB of phase noise performance if the HMC1060 is used instead of the LT3042 and LT3045 that are recommended. Jitter of 40 fs can be achieved at 8 GHz (as well as many other frequencies) and total power consumption is only 815 mW typically but can be configured to use less than 700 mW at a cost of 1 to 2 dBc/Hz of phase noise performance. 
 6) The ADF4372 has a FOM of -234 and operates in a manner similar to the ADF5610 but the VCO PN is a bit higher. 
 
 7) Lots of discrete PLL / VCO options that can provide the same or better PLL / VCO PN performance as you currently have with the HMC767. 
 
 Best regards, 
 
 Marty)

Electronic Design Services - PartnerZone

Products In This Thread

HMC765 vs HMC767

Top Replies