AnsweredAssumed Answered

frequency sweep problem of HMC769

Question asked by danosong on Feb 11, 2015
Latest reply on Mar 17, 2015 by danosong

Hi, all

I'm trying to use HMC769 as a FMCW signal generator. After 2 days' groping for the SPI interface, I have finally made HMC769 output fixed frequency in integer or fractional modes.

I followed the "PLLs WITH INTEGRATED VCO - MICROWAVE APPLICATIONS PRODUCT & OPERATING GUIDE" (page 20) exactly, but can not get frequency sweep.

The start frequency is 8.96 GHz, and stop frequency 10.24 GHz, although a little beyond the specification, but it works in fixed frequency mode. The reference is 10 MHz, and R is 1. After some computations, the register sequence to be written is:

(1) Reg 06 = 0x1F1F             <the PLL in fractional mode>

(2) Reg 0B = 0x1E071

(3) Reg 09 = 0x3264

(4) Reg 03 = 0x1C0

(5) Reg 04 = 0x0

(6) <Press the external Trigger button>

(7) Reg 0A = 0x68DC

(8) Reg 0C = 0x200

(9) Reg 0D = 0x0

(10) Reg 06 =0x1FFF           <the PLL in auto 2-way sweep mode>

(11) <Press the external Trigger button>

After Step(6), the PLL is locked and oupouts 8.96GHz correctly. But after Step (11), the lock is lost, and VCO is free running and outputting its highest frequency.

I do not know what is wrong with the above register sequence. I have tried to change the order, no luck.

BTW, I did not set RFDiv2Sel (Reg 08 bit[17]), because it seems HMC769 automatically set it already. If I set RFDiv2Sel, then the PLL does not work. This is contrary to the manual.

Thanks for any advice.

PS: I am from China. If you do not know how to write my name in Chinese, you can call me "Qian" here.