We recently design a pll using hmc704,but have some problems at low temperature(-10~-55℃), the pll can‘t lock.
the output frequency of vco is 6.4~6.9GHz and we want a frequency of 6.6GHz, the pll works proper at room temperature and high temperature
So we open the loop to debug，the structure is shown below.
we change the frequency by the VT,and test the output voltage by multimenter
when the VT =0 V (6.49GHz) the output voltage is 0 V (Reg0Bh =1)
normally , the output voltage is always 0 V below 6.6GHz
but, at low temperature,
when the VT =0.2 V~0.4V (6.45GHz~6.5GHz) (changes a little as temperature) the output voltage is 5 V,it's abnormal.
at the same time ,we find the Noise of VCO get worse on the spectrum(more than 10dB, span 5MHz)
but if we turn off the reference signal(100MHz),the Noise of VCO return to normal
Now we can not find the reason. hmc704? VCO? others?
we want to know that the hmc704 works proper?
or the requirements for input signals of hmc704,the power?,wave form?