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Issue A

LANSDALE Semiconductor, Inc.

ML12179

Figure 2. Phase/Frequency Detector and Charge Pump Waveforms

fr

(OSCin)

H

L

fv

(Fin ÷256)

H

L

PDout

Sourcing Current Pulse

Sinking Current Pulse

Z

H = High voltage level; L = Low voltage level; Z = High impedance

NOTES: Phase difference detection range: ∼ –2π to 2π

Kp–Charge Pump Gain

|Isource|

|Isink|

4π

++

==

≈

|2.2|

|–2.2|

4π

1.1 mA

πradian

Figure 1. ML12179 Expanded Block Diagram

Crystal

Oscillator

Prescaler

÷256

Phase/Frequency

Detector

Charge

Pump

VCC

OSCin

OSCout

2

1

8

4

C1

C2

VCO

+5.0 V

fr

fv

VP 7

+5.0 V

6

To Loop Filter

GND

GNDP

5

3

NOTE: External 50 kΩ resistor

across Pins 1 and 8 is necessary in

either crystal or driven mode.

1000 pF

Fin

PDout

PHASE CHARACTERISTICS

The phase comparator in the ML12179 is a high speed digital

phase/frequency detector circuit. The circuit determines the “lead”

or “lag” phase relationship and time difference between the lead-

ing edges of the VCO (fv) signal and the reference (fr) input. The

detector can cover a range of ±2

π radian of fv/fr phase difference.

The operation of the charge pump output is shown in Figure 2.

fr lags fv in phase OR fv>fr in frequency

When the phase of fr lags that of fv or the frequency of fv is

greater than fr, the Do output will sink current. The pulse width

will be determined by the time difference between the two rising

edges.

fr leads fv in phase OR fv<fr in frequency

When the phase of fr leads that of fv or the frequency of fv is

less than fr, the Do output will source current. The pulse width

will be determined by the time difference between the two rising

edges.

fr = fv in phase and frequency

When the phase and frequency of fr and fv are equal, the charge

pump will be in a quiet state, except for current spikes when sig-

nals are in phase. This situation indicates that the loop is in lock

and the phase comparator will maintain the loop in its locked

state.