LV25450PNW

Phase Comparator and Charge Pump Circuits

(1) Phase comparator and charge pump operation

In the PLL circuit block shown in figure 1, the phase comparator compares the phases of the reference frequency (fr)

and the comparison frequency (fp), and outputs the amount of the phase difference from the charge pump.

Figure 1 PLL Circuit Block

Reference Divider

Programmable Divider

Phase

Detector

Charge

Pump

LPF

VCO

Mixer

Leakage during

strong-field input

RF

fr

fp

Figure 2 shows the phase comparator/charge pump output characteristics. The phase comparator outputs a voltage V

φ

that is proportional to the phase difference

φ between fr and fp. The phase comparator's characteristics can be

switched by changing the phase comparator dead zone mode setting. The phase comparator can be set to modes (DZA,

DZB) in which both the charge pump p-channel and n-channel sides are turned on when the phase difference is small,

or can be set to a mode (DZD) that does not output the phase difference when the phase difference is small.

Figure 2 Phase Comparator/Charge Pump Characteristics

φ err[ns]

V

φ[V]

V

φ[V]

V

φ[V]

V

φ[V]

Dead Zone(--)

DZA

mode

DZB

mode

DZC

mode

DZD

mode

φ err[ns]

φ err[ns]

φ err[ns]

Dead Zone(-)

Dead Zone

≈ 0

Dead Zone(+)

fp > fr

fp > fr

fp > fr

fp > fr

fr > fp

fr > fp

fr > fp

fr > fp

No.A1668-37/40