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.

Regards,

SMcBride  

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

HMC681ALP5E

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:

https://ez.analog.com/message/288407

Thanks,

SMcBride