mwvco1
Newbie level 5
Hi,all
We recently design a pll using hmc704,but have some problems below low temperature(-45℃), the pll can‘t lock.
the output frequency of vco is 6.49~6.9GHz and we want a frequency of 6.65GHz, 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(CP) by multimenter
when the VT =0 V (6.49GHz) the output voltage is 0 V (hmc704 Reg0Bh[4] =1)
normally , the output voltage is always 0 V below 6.65GHz
but, at low temperature(-45℃),
when the VT =0.2 V~0.4V (6.54GHz~6.56GHz) 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?
why?
Really want to get your help.
We recently design a pll using hmc704,but have some problems below low temperature(-45℃), the pll can‘t lock.
the output frequency of vco is 6.49~6.9GHz and we want a frequency of 6.65GHz, 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(CP) by multimenter
when the VT =0 V (6.49GHz) the output voltage is 0 V (hmc704 Reg0Bh[4] =1)
normally , the output voltage is always 0 V below 6.65GHz
but, at low temperature(-45℃),
when the VT =0.2 V~0.4V (6.54GHz~6.56GHz) 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?
why?
Really want to get your help.