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Issue A

LANSDALE Semiconductor, Inc.

ML12210

PHASE CHARACTERISTICS/VCO CHARACTERISTICS

The phase comparator in the ML12210 is a high speed digital phase frequency detector circuit. The circuit determines the “lead” or “lag”

phase relationship and time difference between the leading edges of the VCO (fp) signal and the reference (fr) input. Since these edges

occur only once per cycle, the detector has a range of ±2

π radians. The phase comparator outputs are standard CMOS rail–to–rail levels

(VP to GND for

φP and VCC to GND for φR), designed for up to 20MHz operation into a 15pF load. These phase comparator outputs

can be used along with an external charge pump to enhance the PLL characteristics.

The operation of the phase comparator is shown in Figures 3 and 5. The phase characteristics of the phase comparator are controlled by

the FC pin. The polarity of the phase comparator outputs,

φR and φP, as well as the charge pump output Do can be reversed by switching

the FC pin.

Figure 3. Phase/Frequency Detector, Internal Charge Pump and Lock Detect Waveforms

fr

fp

LD

Do (FC = H)

φR (FC = H)

φP (FC = H)

Do (FC = L)

φR (FC = L)

φP (FC = L)

H

L

H

L

H

L

Source

Sink

H

L

H

L

Source

Sink

H

L

H

L

Z

Z

NOTES: Do and BISW are current outputs.

Phase difference detection range: –2

π to +2π

Spike difference depends on charge pump characteristics. Also, the spike is output in order to diminish dead band.

When fr > fp or fr < fp, spike might not appear depending upon charge pump characteristics.

BISW (LE = H or Open)

BISW (LE = H or Open)

Internal Charge Pump Gain

Isource

Isink

4

π

≈

+

= 4mA

4

π