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HMC346AMS8GE  Is it possible that the termination resistor of the reference attenuator is not 500Ω?

Thread Summary

The user inquires about the HMC346AMS8GE reference attenuator's termination resistor and the safety of changing the positive input connection resistance of the op-amp. The final answer confirms the internal termination resistor is 600Ω, but 500Ω is used externally for better return losses. For the V2-I loop, a -5V rail op-amp is recommended, and for max attenuation, V1 should be set to -4V or -4.5V instead of -3.5V.
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Category: Hardware
Product Number: HMC346AMS8GE

Hello.

I have two questions about HMC346AMS8GE.

1) Is it possible that the termination resistor of the reference attenuator is not 500Ω?

2) Is it safe to change the positive input connection resistance of the op-amp from 500 ohms to 330 ohms?

An event occurs where V2 only goes up to -3.5V even when -3.5V is applied to V1, and only about -10dB of attenuation is ensured.

In order to match the characteristics of V2 with respect to V1, the 500Ω of the V2 driver circuit was lowered by 330Ω to obtain almost the same characteristics.

The same circuit was used for the other lot, but no problem was observed.

Best regards,

  • Hi,

    1) The internal termination resistor is 600ohm, but the external loop uses 500ohm as better return losses at RF input and RF output are achieved. 

    2) Considering part to part variation, the gate pinch-off may shift for max attenuation. Thus, you need -5V rail op-amp at the V2-I loop. Similarlay, for the max attenuation, you need to apply less than -3.5V , like -4V or -4.5V to V1.

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