FAQ: HMC814 / HMC814LC3B Active Frequency Multiplier, 13 GHz – 24.6 GHz Output

FAQ: HMC814 / HMC814LC3B Active Frequency Multiplier, 13 GHz – 24.6 GHz Output

This FAQ covers common questions related to the HMC814 (die) and HMC814LC3B (packaged) multiplier.

APPLICATION SPECIFIC:

Question: I discovered that when I input a 12GHz signal to the HMC814LCB, the 4^th harmonic (48 GHz) is fairly strong (> -10 dBm). Can I use this in my application?

Answer: Customers are always free to implement components in any manner that they desire and many routinely use components outside of the specified operating conditions. However, by doing so these customers assume the full responsibility of performing any necessary additional characterization and qualification testing to understand and minimize any risk. Analog Devices does not warranty these products when used outside of the datasheet specifications. It is highly recommended that a reasonable sample size be used and preferably samples with date codes that cross multiple wafer lots be used for this extended testing. The conditions should match those of the application and as a minimum cover the extremes that are expected for biasing, drive level and temperature variation.

Question: Can I provide an external match on the input or output to improve gain or extend the frequency performance?

 Answer: Although the HMC814 multiplier is a single function device, it consists of 3 cascaded circuits (an input amplifier, multiplier, output or buffer amplifier) that must operate over nearly an octave which is not trivial. Since the user can not access the inter-stage nodes it will be impossible to provide a simultaneous conjugate match to each of these stages. Furthermore while users may assume that these internal nodes are matched to 50 ohms that may not be the case. The amplifier stages do provide good isolation for the multiplier stage however external matching could still impact return loss, output power vs drive level, harmonics or spurs in certain regions of the frequency band. Generally speaking,

Analog Devices’ frequency multipliers should be treated like a 50 ohm gain block, drop it in to your circuit and use it “as is” within the specifications shown on the datasheet. Any gains achieved through external matching would most likely be narrow band and the user must assume any performance or reliability risk associated with doing so.

Question: If I apply external matching or remove the input signal will the HMC814LC3B oscillate?

Answer: No.

Question: Are there any protection diodes that are on the I/O for the HMC814

Answer: The pin descriptions below more accurately represent the I/O interface of HMC814.

A shunt 2.16k ohm resistor was used instead of diode for ESD protection due to high frequency operation.

Question: I noticed that the HBM ESD classification of the HMC814 is only Class 0 (Passed 150V). Is there anything I can do to improve the ESD protection?

Answer: Yes, but since the HMC814 covers nearly an octave frequency range any additional protection applied to RF ports may impact performance so it’s recommended that the RF performance be verified across the intended frequency range at all supply and temperature extremes. ESD protection at DC inputs can be improved by adding TVS diodes. On RF ports in narrower bandwidth applications, add a shunt inductor that exhibits low series resistance and a self-resonant frequency that is approximately mid-band; be sure to include any necessary DC blocking capacitors. If the entire frequency range is being used more complex solutions will be necessary and / or some tradeoff in performance may be required.  

Question: Where are the spurs in the phase noise plot for the HMC814LCB datasheet coming from?

Answer: They appear to be a function of the 60 Hz AC line and are leaking through the power supply. Note that they are less than 90 dBc!

PACKAGING

Question: Does the HMC814LC3B use an open cavity package?

Answer: Yes.

Question: Is the LC3 package hermetically sealed?

Answer: No.

Question: Does the LC3 package include a hydrogen getter?

Answer: No; getters are generally restricted to hermetic packages.

Question: Is the package lid grounded?

Answer: No, it’s ceramic.

Question: What is the thickness of the HMC814 die?

Answer: 4 mils

BIASING

Question: In the assembly diagram for the HMC814, it shows two separate sets of bypass capacitors for Vdd1 and Vdd2. Can I distribute the same Vdd to both Vdd1 and Vdd2 and use a single set of capacitors?

Answer: Yes. We have simulated the circuit and there does not appear to be any impact to the S-parameters or output power. It should be noted however that all product validation was based on the configuration shown in the data sheet. It is recommended that VDD1 and VDD2 each retain their own 100 pF capacitors (placed as close to the die as possible) then tie VDD1 and VDD2 together and follow with a single 1000 pF cap and a single 2.2 pF cap for stability over temperature. See assembly diagram below.

Question: The HMC814 datasheet lists the nominal current as the sum of Idd1 and Idd2. What is the ratio of current (and thus the internal bias voltage)? Is the split 50/50, 20/80 or ?

Answer: The HMC814 is internally self-biased so the two Vdd pins shared the same supply node during characterization so unfortunately we don’t have separate Idd values in any of the data we have on hand. If this is something that’s important for your application, consider purchasing an evaluation board and validating this using the respective frequency range and input drive level for the application.

EVALUATION BOARD

Question: Are the CAD / Gerber files for the HMC814 evaluation board available?

Answer: Yes, please visit the HMC814 product page on the Analog Devices website to download them.

GENERAL

Question: Are S-parameters available for the HMC814?

Answer:  Yes, please visit the product page for the HMC814 on analog.com website. Please be aware that per the file notes, the reference plane appears to be at the connector of the evaluation board (not de-embedded to the pin).  

Question: Is it meaningful to talk about NF, Gain, OIP3 and OP1dB of a multiplier?

Answer: Most of the HMC series multipliers consist of an input amplifier stage, a multiplier stage and output amplifier stage. While one could characterize these parameters for each stage of the cascaded assembly, normally it’s not done because of where multipliers fall in a typical radio. These multipliers are generally placed after one our microwave VCO’s and used to increase the LO frequency into a mixer or Up / Down converter. In this application we aren’t concerned with noise figure but with the phase noise which will change at 20 * Log (N) where N is the multiplication rate. Additive phase noise from the multiplier will also need to be added to this value. For this reason, power, conversion gain (CG), Fo, 3Fo isolation, return loss and residual phase noise are the key specifications.

Question: Is the HMC814 / HMC814LC3B unconditionally stable?

Answer: Yes.

Question: Is there any floating metal on the HMC814 die? Floating metal is related to unconnected pins on packages.  Per the mil requirements any unused pins must be grounded otherwise the possibility for a charge to build up exists and this can result in damage to the device.  

Answer: No, the only exception being the logo and number.

Question: Where can I find reliability data for the HMC814?

Answer:  For legacy HMC products you must visit https://www.analog.com and go to their ‘Full Product page’ (in this case for the HMC814) and look under the Reference Materials tab for the report titled PHEMPT-F (QTR: 2013-00269) for the semiconductor qualification report. The LC3B package qualification report is also available. Note that qualification data for legacy ADI products is located under the ‘Design Center’ tab on the website home page.

Question: Is it acceptable to operate the HMC814 at a bias level of 4.5V or lower?

Answer:  The HMC814 should be safe to bias at 4.5V as this bias point was used during characterization. Further bias reduction (sometimes required in order to meet derating guidelines) may be possible but any characterization or reliability testing will become the customers responsibility as Analog Devices does not warranty or guarantee performance beyond the test conditions specified in the datasheet. 

Note that like many GaAs amplifiers, reducing Vdd results in an increase in the gain; this may sound like a good thing but in reality it is actually not and it’s compounded at cold temperatures. Parametric oscillations at Fo/2 where Fo is the input frequency, can occur at Vdd < 4.5 V (oscillations occur in the input / output amplifiers) and are exacerbated with higher drive levels and lower temperatures. These oscillations can appear / disappear over very narrow frequency ranges and may also be dependent on drive level.

Attached is a copy of the above information covering frequently asked questions for the HMC814 / HMC814LC3B frequency multiplier.

Feel free to reach out to me if there's something you'd like me to add to this or for clarification. I hope you find this helpful. 

Best Regards, 

Marty