FM modulation with PLL+VCO

1) Modulate VCO control line. PLL lopp bandwidth must be narrower than modulation bandwidth and injection circuity must be very high impedance, or AC coupled, so it will not cause leakage from charge pump. This techniquie is "high pass"

2) Modulate reference. This is "low pass"

3) Do both, reserach "two point modulation". This is "all pass".

please give some ref links or articles.

Just Google "two point modulation"

http://www.ortodoxism.ro/datasheets/CML/mXyzuuuz.pdf