I measure step attenuator HMC629A on the EVB (EV1HMC629ALP4E). This attenuator is specified from DC to 10GHz, but the performance seems to be not fulfilled at low frequencies. In order to verify the parameters, I changed the capacitors C1, C2, C4...C8 to 2.2uF/25V. The attenuation graph (with applied change) setting vs.measurement is OK even at low frequencies.
But the IIP3 parameters degrades significantly at lower frequencies in spite of it is specified DC...10GHz in the datasheet. It shall be typ. 55dBm, but I measure ~22dBm.
Is the specification of IIP3 in the datasheet correct?
HMC629A requires DC blocking capacitors at RF pins and ACG capacitors. When these caps are large enough, the part can provide decent small signal performances (insertion loss, return losses, attenuation accuracy) down to low frequencies but degrade large signal performances (P1dB and IP3) below ~200 MHz as a normal characteristic of GaAs parts.
See the plots below for P0.1dB and IP3 data measured down to 10 MHz. The datasheet specs for P0.1dB and IP3 and absolute maximum input power will not be valid below ~200 MHz.
thank you for the answer. Do you think about the correction in the datasheet? There is written for the P0.1dB compression frequency condition "DC...10GHz" which seems to me wrong. I expect something like "200MHz...10GHz".
We will update our legacy HMC datasheets including HMC629A into ADI format (this would take several months) and specify large signal performances from ~200MHz.