HMC856 Eval board Interfacing

Hi,

One way to do is connect positive ports B0-B4 to a fixed voltage with a resistance, say 1.2k to GND and connect transistor switches to negative ports(B0~B4) with 2.7kohms each. Transistor switches can either be open or short to Vee. This way (B0-B4) change state. LVTTLs can drive switch transistors. 

If you supply shift the part between 3.3V and GND, and if LVTTLs can supply enough current, you wouldnt need interfacing transistors/level shifters. The RF signal though should be AC couple in that case. 

Sinan 

Hi,

I saw the HMC856 Eval board schematic (page 12 of the datasheet) and the B0-B4 ports are connected differently.

The positive ports B0-B4 are connected singularly to a test point with a 2.7KOhm resistor while the negative ports B0-B4 are connected together with 1.2KOhm to a test point. Your suggestion is not applicable to HMC856 Eval board. Is it correct?

Could you help me to understand the right way to management the B0-B4 ports of the HMC856 Eval board?

Could you help me to understand the right way to management the B0-B4 ports of the HMC856 with LVTTL signals?

Best Regards,
Daniele 

Control pins have internal 600ohms and there is a voltage division with externally connected resistors which are pulled down to -3.3V.

• J5 has jumpers on it, pulling down B0+~B4+ (positive pins) to -3.3V with 2.7k or not. With the internal 600ohm pull-up, positive pins are either set to -600mV(jumper installed) or 0mV(jumper not installed)
• As for the negative pins, 5 control pins are connected in parallel with an equivalent pull-up of 120ohms(600/5). With the external pull-down(1.2k), negative pins are set to -300mV. This jumper is not meant to be removed, it should always be on
• Thus, negative pins set to -300mV, positive pins are set to 0mV or -600mV. The differential control voltage is +300mV or -300mV.

Hi,

in the eval board, the 600 Ohm internal pull ups are connected to VT. The VT-J8 pin is floating (I didn't see a specific interconnection) while you supposed that this pin is connected to GND. It is correct?

Best Regards,

Daniele

VT should be tied to GND, you are correct. 

VT should be tied to GND, you are correct.