HMC625B for low frequency application

Question

Hi, 
 I would like to know if the HMC625B can be used from 10kHz. I planed to use this part in a broadband transmitter from 10Khz to 1Ghz. The title of the datasheet mentioned the frequency range from DC to 5GHz, but according to the curves in datasheet the Gain goes down to about 5dB near DC and the input/output return loss is so bad at these low frequencies. So how could I use this part in low frequencies like 10kHz, 100KHz, etc ? Do I need to use extra matching circuits or others modifications ? Or do you have other VGA parts to recommend ? ADL5331 can be used in theses low frequencies ? 
 
 Thanks in advances, 
 Best regards, 
 
 Xl

viktor_vojta · Accepted Answer

Hello, 
 the use of such device at low frequencies is associated with problems. It is GaAs device, you may expect higher flicker noise. Even if you adjust the 100pF capacitors for internal bias in attenuator, the harmonic distortion (and of course IM distortion) will be higher at low frequencies. Both factors lead to degraded dynamic range at low frequencies. Third issue, you need to solve, is bias of output amplifier. High value supply-inductors are not practical and bias through current source may cause other problems.)

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HMC625B for low frequency application