PLL loop filter not stable
时间：04-10
整理：3721RD
点击：
Hello
I make a PLL+VCO circuit with MB15F03(fujitsu) and POS535 (minicircuits),but the loop filter does not give stable dc voltage and it is like sinewave,I want to produce 433MHZ ,but I do not have stable output,because Vtune of VCO is not stable,
I used PLL softwares to design the low pass loop values,what is the way to solve the problem?why PLL does not lock?
I make a PLL+VCO circuit with MB15F03(fujitsu) and POS535 (minicircuits),but the loop filter does not give stable dc voltage and it is like sinewave,I want to produce 433MHZ ,but I do not have stable output,because Vtune of VCO is not stable,
I used PLL softwares to design the low pass loop values,what is the way to solve the problem?why PLL does not lock?
If input level that comes from VCO is not sufficiently high, prescaler may oscillate and therefore PLL can not decide which frequency will be locked..
Check the level at the input of the PLL
rule of thumb is the ratio of reference freq and loop band width should be around 10. this is a very important consideration.