Question TXdata triggering function on the ADF4159: is itcorrect that a sweep can be repeated an unlimited number of times by simplyapplying another logic pulse on the TXdata pin, or is it also necessary (as inthe ADF4158) to first reload the 32bit data with R0[31]=1 (or R7[20]=1 ?) eachtime? Our goal would be to minimize software overhead when repeating similarsweeps. Answer It is not necessary to load another 32 bits. The following scope capture shows how TXdata (top trace) starts the sawtooth ramp without sending anyadditional SPI data to the ADF4159. The sweep starts on the first rising reference edge after TXdata=1.

PLL with sweeping capability

Question In the search for a PLL with sweeping capability we were first looking at theADF4158, but found two limitations with that chip: first, its phase noise israther high and second it does not have a hardware input pin to trigger theexecution of a frequency sweep. We need this in order to synchronize the rampgeneration with the signal sampling on the receiver side.Fortunately, we found another product in your offering that solves both issues:the HMC703. Do you recommend the HMC703 for a new design or should we better look for a"genuine" chip by Analog Devices (the HMC703 is a former Hittite product). Isthere a cheaper chip with the required capabilities (and frequency range up to4 GHz) ? Answer Either the HMC703 or ADF4159 can trigger sweeps using a hardware pin. The ADFpart has higher phase noise but can synthesize more complicated ramps. Ifsweeper functionality is not a concern I recommend the HMC703. This part isone of our best performing parts in the ADI portfolio.