Re: PLL block
If by "amplifier" you mean an op amp circuit, there are three reasons:
1) an op amp allows a bigger tuning voltage range than a charge pump output phase detector can give you by itself
2) an op amp set up as an integrator can give you infinite (or close to it) DC gain, so the phase error approaches zero. Without the high DC gain of an op amp, when the loop locks there will be a larger static phase error. (And in most digital phase detectors, a large static phase error manifests itself as significant pulses at the clock reference frequency on the VCO tuning line which then cause large RF spurious output sidebands--not desireable).
3) it is easier to design a more complex loop filter, with numerous poles and zeros and DC summing junctions, if there is an op amp. Without an op amp, you are pretty much limited to two poles and one zero in your control loop filter design.