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HMC681 IF Amp

What exactly is the function of P/S in HMC-681ALP5E IC?  Can this be used as Enable / Disable pin for the IC?

Also HMC681 only uses only 6 serial bits for programming. Is it safe to assume all Data other than the last six before LE goes high are ignored by the chip (let us say first 18 out of a 24 bit stream)?  

  • Hi Shyam61,

    Inside of the HMC681ALP5E are four die: Two amplifiers, a 6-bit digitally controllable attenuator, and a controller for the attenuator. The controller die gets used in several HMC/ADI products and is capable of being configured for either or both of Parallel and Serial gain control...thus the P/S pin nomenclature. However, in the HMC681A this controller is configured for Serial control only, though we've chosen to keep the P/S nomenclature. In order for the controller to correctly work in Serial mode, the P/S pin must be set high (typically to the same voltage as Vdd). The P/S pin is not used to perform an overall enable/disable function with the HMC681A. If a Parallel mode of gain control is desired then you should instead use the HMC626ALP5E.

    Your assumption is correct regarding the last six control bits. Data is clocked in MSB-first, LSB-last, and the final six bits prior to a rising edge on LE constitute the control word that sets the gain state. All previously clocked bits would be ignored.

    I hope that helps. Let me know if you have more questions.



  • Hi, I know I am a bit off topic, but if you know the answer, please share:  

    Relative Gain is expressed in negative dB in the


    data sheet truth table: 

    Usually negative dB mean attenuation, however, the device is supposed to be a 45db Amplifier. How to achieve amplification? 

    Thank you! 

  • To keep this inquiry tied to its identical (though separate) separate inquiry, please see the answer at the thread linked below: