FAQ: HMC Phase Frequency Detectors

Document created by MRichardson Employee on Mar 24, 2015Last modified by MRichardson Employee on Sep 7, 2016
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With Analog Devices’ acquisition of Hittite Microwave Corporation came several new Phase Frequency Detector products. These useful building blocks are implemented when designing phase locked loop synthesizers for microwave radios for point to point, military, satellite and SONET applications. This FAQ attempts to address some of the common questions regarding these devices.

 

 

Question:  What part numbers make up this product line?

 

Answer:  The HMC439QS16GE and HMC3716LP4E; complementary
parts that include a counter are the HMC440QS16GE and HMC4069LP4E respectively.

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Question:  Are these available as die?

 

Answer:  Yes, the HMC3716 has been made available as “untested” die. Please contact the factory for additional information.

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Question:  Is hermetic packaging an option?

 

Answer:  Yes – please contact the factory for more information.

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Question:  Are these available as “non-RoHs” or “lead” parts for military and aerospace applications?

 

Answer:  Yes. The HMC439LP3G is available as a “non-RoHs” or “lead” part and the HMC3716LP4E may be as well. Please contact the factory for availability and pricing.

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Question: What process do these parts utilize?

 

Answer: The HMC439QS16GEQS16GE and HMC3716LP4ELP4E are built on a GaAs HBT process.

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Question:  What are the pros and cons of this process?

 

Answer:  One of the primary differences between processes is where the 1/f or “flicker” noise corner falls. The GaAs process has a flicker corner of about 3 kHz. This results in improved close in phase noise  (at offsets less than 3 kHz) due to the inherent 30dB / decade noise slope at offsets between the carrier and the flicker corner. By comparison, the flicker corner in the SiGe process falls closer to 10kHz and will have slightly worse close in phase noise but better performance at 100kHz and beyond. The GaAs process also has a well established reliability for space applications.

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Question:  What is the ESD rating of these devices?

 

Answer:  The HMC439QS16GE is Class 0 (HBM) while the HMC3716LP4E is Class 1B (HBM) / Class C2 (CDM) and are easily damaged. ESD precautions should be strictly followed during all handling operations to prevent damage to the device.

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Question: What is the input impedance of the HMC439QS16GE and HMC3716LP4E devices?

 

Answer: The HMC439QS16GE and HMC3716LP4E provide a 50 ohm differential impedance at the REF and VCO ports. 

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Question:  What are the differences between the HMC439QS16GE and the HMC3716LP4E?

 

Answer:  

  1. The HMC3716LP4E integrates the pull-up resistors that are required on the HMC439QS16GE at the U / D and NU / ND output pins and has       eliminated the U/D output.

  2.  Lock Detect and Invert functionality have been added to the HMC3716LP4E.

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Question: Is it possible to drive the HMC439QS16GE or the HMC3716LP4E single ended?

 

 

Answer:  Yes – just AC ground the unused port (no need to add a 50Ω resistor).

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Question:  What is the benefit of using the differential input?

 

Answer:  Other than increased input power (3dB higher vs. single ended) and improved isolation due to differential operation there's no difference in performance.

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Question:  Is it possible to convert the differential output to single ended so a passive loop can be used?

 

Answer:  No, the output was designed to drive a high impedance load, specifically an op amp. It’s unable to source any current. Differential outputs in conjunction with an active loop are required in order to provide a stable phase locked source with minimal spurs as well as provide
the means to tune the VCO both up or down as needed in order to retain lock.

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Question:  I only need 2 Volts of tuning; can I drive the VCO tune port directly?

 

 

Answer:  No, the outputs are unable to source any current and were designed specifically to operate differentially. The pulses that simultaneously appear on the outputs provide a cancellation effect which helps to minimize spurs.

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Question:  How is the invert (INV) functionality of the HMC3716LP4E used?

 

Answer:

 

  1. Normal Mode: If VCO frequency > REF: ND is the active output. 
  2. Invert Mode: If VCO frequency > REF: NU is the active output.
  3. Invert mode could provide a physical layout advantage if swapping the inputs is helpful for layout reasons.  Swap VCO and REF at input and continue to use ND as the output.

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Question:  Does the invert function invert the logic levels as well?

 

Answer:  No.

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Question:  What should I do with the INV pin on the HMC3716LP4E if I don’t need the invert functionality?

 

Answer:  Simply tie it to ground.

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Question:  Do you have a lock detect circuit you can recommend for the HMC439QS16GE?

 

Answer:  No. If lock detect functionality is needed then we recommend the HMC3716LP4E.

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Question:  How do I implement the lock detect functionality on the HMC3716LP4E or HMC4069?

 

Answer:  The LD pin utilizes an open collector configuration and must be pulled up to Vcc via an external 1k Ohm resistor.
It’s also recommended to add a series 100Ω resistor to limit surge current followed by a shunt capacitor to provide the desired logic level for the reference frequency being used.

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Question:  If I power these devices down, what state do they “wake up” in?

 

Answer:  The turn on state is random however in just a few clock cycles the circuit figures out where it needs to be and provides the
appropriate output.

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Question:  Can I use these devices as a phase detector?

 

Answer:  No. Customers who've tried this have noticed that there is hysteresis associated with the output phase error and amplitude.  This is because these are phase frequency detectors – not phase detectors and are designed for use in a PLL synthesizer. We recommend using a mixer instead as it has no hysteresis and will provide the +/- voltage swing that is desired.

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Question:  What is the temperature drift of the output voltage for these devices?

 

Answer:  This generally isn't a concern for the primary application for these parts so this parameter wasn't characterized. If
the HMC439QS16GE is being used, the Tc of the external pull-up resistors could be minimized.

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Question:  On the HMC439QS16GE can I use the U / D pins instead of the NU / ND pins?

 

Answer:  Only if you're willing to take a 6 dB degradation to the phase noise performance.

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Question:  Why is there a 6dB phase noise degradation at the U / D pins on the HMC439QS16GE?

 

 

Answer:  The U / D pins are “On” most of the time and operate at current levels that are an order of magnitude higher than the NU /
ND pins. This degrades the phase noise on these pins by 6dB.

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Question:  Why were the U / D pins eliminated on the HMC3716LP4E?

 

Answer:  The HMC3716LP4E includes lock detect functionality so they aren't needed. Furthermore, use of resistor values greater than 20 ohms on these pins results in phase noise degradation.

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Question:  Can I alter the value of the pull-up resistors on the output pins (U, D, NU, ND).

 

Answer: No. These have been optimize for phase noise performance and set the output voltage swing of 2V, swinging between 3Vdc and 5Vdc.

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Question:  How does the phase noise scale?

 

Answer:  The residual or additive phase noise scales at 10*LOG (f / fo) where f > fo.

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Question:  What waveform should I use for the best phase noise?

 

Answer: A waveform with a high slew rate (square wave) will always provide the best phase noise at reference frequencies below 100MHz.

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Question:  What is the minimum slew rate for frequencies below 100MHz?

 

Answer: We haven't characterized these parts to determine the minimum slew rate.

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Question:  How can I synthesize a loop filter if I use these parts?

 

Answer:  Follow the link below for step by step instructions on how to use the legacy HMC PLL Design tool to synthesize a loop filter when using legacy HMC products that output directly from the phase frequency detector.

 

Link:  https://ez.analog.com/message/177133#177133

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