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# HMC8191 DC FEED FOR IF1/2 ?

Hi, all.

There is a circuit diagram of the circuit configuration of the optional LO null circuit on page 41 of the data sheet of HMC8191,

but there is no description about the electrical specifications and characteristic examples of bias tee supply.

1. What is the absolute maximum rating of the DC voltage supply for the IF1 / 2 port?

2. We are confused because we do not understand the relevance to the following specifications.
IF Source / Sink Current 3 mA.
The common-mode voltage for each IF port is 0 V.

How should we adjust ? ,and test setup power supply circuit for DC offset ?

Best regards,

sss

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[edited by: sss@jpn at 7:24 AM (GMT -4) on 17 Mar 2022]
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• Hi SSS,

On the datasheet of the HMC8191 page 4 in table 2 (Absolute Maximum Ratings) table we list a maximum source/sink current of 3mA. That means the total current to by synced or sourced on the IF1/IF2 pins cannot exceed that current. For LO nulling the voltages on either IF1 or IF2 do not have to match such that you will get some current draw. Typically we have found that the voltages needed to null the LO are on the order of -0.1 to 0.1V requiring a fine voltage step of 0.001V based on how deep of a null you are desiring.

Typically for adjusting the DC voltage on each IFX port, we would do the following(At each step below monitor the LO leakage to ensure  level is reducing):

1. Adjust IF1 from 0V to 0.1V in at least 0.01V steps, stop adjusting if the LO leakage starts to get worse from the previous voltage.

2. If the above positive step resulted in no improvement, adjust IF1 from 0V to -0.1V in at least 0.01V steps, stop adjusting if the LO leakage starts to get worse from the previous voltage.

3.  Adjust IF2 from 0V to 0.1V in at least 0.01V steps, stop adjusting if the LO leakage starts to get worse from the previous voltage.

4. If the above positive step resulted in no improvement, adjust IF1 from 0V to -0.1V in at least 0.01V steps, stop adjusting if the LO leakage starts to get worse from the previous voltage.

At this point if the desired LO leakage is still not met I would loop back to step 1 and run through the steps again, but do not go back to 0V on the DC voltage, but start adjusting +/- in 0.1V steps from the voltages found in the first round of adjustments to fine tune the offsets.

• Hi SSS,

On the datasheet of the HMC8191 page 4 in table 2 (Absolute Maximum Ratings) table we list a maximum source/sink current of 3mA. That means the total current to by synced or sourced on the IF1/IF2 pins cannot exceed that current. For LO nulling the voltages on either IF1 or IF2 do not have to match such that you will get some current draw. Typically we have found that the voltages needed to null the LO are on the order of -0.1 to 0.1V requiring a fine voltage step of 0.001V based on how deep of a null you are desiring.

Typically for adjusting the DC voltage on each IFX port, we would do the following(At each step below monitor the LO leakage to ensure  level is reducing):

1. Adjust IF1 from 0V to 0.1V in at least 0.01V steps, stop adjusting if the LO leakage starts to get worse from the previous voltage.

2. If the above positive step resulted in no improvement, adjust IF1 from 0V to -0.1V in at least 0.01V steps, stop adjusting if the LO leakage starts to get worse from the previous voltage.

3.  Adjust IF2 from 0V to 0.1V in at least 0.01V steps, stop adjusting if the LO leakage starts to get worse from the previous voltage.

4. If the above positive step resulted in no improvement, adjust IF1 from 0V to -0.1V in at least 0.01V steps, stop adjusting if the LO leakage starts to get worse from the previous voltage.

At this point if the desired LO leakage is still not met I would loop back to step 1 and run through the steps again, but do not go back to 0V on the DC voltage, but start adjusting +/- in 0.1V steps from the voltages found in the first round of adjustments to fine tune the offsets.

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