MC12202D Просмотр технического описания (PDF) - Motorola => Freescale

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MC12202D

Serial input PLL frequency synthesizer

Motorola => Freescale 

MC12202

PHASE CHARACTERISTICS/VCO CHARACTERISTICS

The phase comparator in the MC12202 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 ±2π 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.

fr

fp

LD

Do (FC = H)

BISW (LE = H or Open)

φR (FC = H)

φP (FC = H)

Do (FC = L)

BISW (LE = H or Open)

φR (FC = L)

φP (FC = L)

NOTES: Do and BISW are current outputs.

Phase difference detection range: –2π 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.

[ Ť ) Ť + Internal Charge Pump Gain

Isource Isink

4p

4mA

4p

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

H

L

H

L

H

L

Source

Z

Sink

H

L

H

L

Source

Z

Sink

H

L

H

L

MOTOROLA

6

HIPERCOMM

BR1334 — Rev 4

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