Hi,

we two students from Switzerland would like to use the Attenuator HMC472ALP4E in the frequency range of 1.7MHz to 1.8 MHz for our bachelor thesis. While designing our circuit we consulted the Datasheet(v00.1212). In the Application circuit(page 7) the ACG1 to ACG4 are connected over a single 330pF Capacitor to ground while ACG5, ACG6 and ACG7 are connected each separately over a 330pF capacitor to ground. We were wondering why ACG1 to ACG4 are connected together and the other ACGs are separately grounded? Can they also be all connected and AC grounded via one common capacitor?

Is it sufficient using 330nF capacitor(s) (Impedance at lowest used frequency of 1.7MHz is 0.28Ohm for 330n)?

Thanks in advance for answering our question!

Kind regards

Silvan and Livio

Hi,

ACG pins provide each of the attenuator bits a clean AC ground path for optimal operation. ACG capacitors of 330nF would be OK at your application frequency of 1.7-1.8 MHz.

We suggest using separate ACG capacitors for the HMC472ALP4E's higher attenuation bits (ACG5 and ACG6 for 8dB and 16 dB attenuation bits) not to degrade the part performance due to signal leakage on lower attenuation bits. ACG pins for the HMC472ALP4E's lower attenuation bits (ACG1,2,3,4 for 0.5,1,2,4dB attenuation bits) can be connected to ground with a common capacitor.

Best.