MC145191F View Datasheet(PDF) - Motorola => Freescale

Part Name

Description

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MC145191F

1.1 GHz frequency synthsizer

Motorola => Freescale 

fR

REFERENCE

REFin ÷ R

fV

FEEDBACK

fin ÷ (N × 64 + A)

PDout

φR

φV

LD

VH

VL

VH

VL

*

SOURCING CURRENT

FLOAT

SINKING CURRENT

VH

VL

VH

VL

VH

VL

VH = High voltage level

VL = Low voltage level

*At this point, when both fR and fV are in phase, the output source and sink circuits are turned on for a short interval.

NOTE: The PDout either sources or sinks current during out–of–lock conditions. When locked in phase and frequency,

the output is high impedance and the voltage at that pin is determined by the low–pass filter capacitor. PDout, φR,

and φV are shown with the polarity bit (POL) = low; see Figure 14 for POL.

Figure 18. Phase/Frequency Detectors and Lock Detector Output Waveforms

DESIGN CONSIDERATIONS

CRYSTAL OSCILLATOR CONSIDERATIONS

The following options may be considered to provide a ref-

erence frequency to Motorola’s CMOS frequency synthe-

sizers.

Use of a Hybrid Crystal Oscillator

Commercially available temperature–compensated crystal

oscillators (TCXOs) or crystal–controlled data clock oscilla-

tors provide very stable reference frequencies. An oscillator

capable of CMOS logic levels at the output may be direct or

dc coupled to REFin. If the oscillator does not have CMOS

logic levels on the outputs, capacitive or ac coupling to REFin

may be used (see Figure 8).

For additional information about TCXOs and data clock

oscillators, please consult the latest version of the eem Elec-

tronic Engineers Master Catalog, the Gold Book, or similar

publications.

Design an Off–Chip Reference

The user may design an off–chip crystal oscillator using

discrete transistors or ICs specifically developed for crystal

oscillator applications, such as the MC12061 MECL device.

The reference signal from the MECL device is ac coupled to

REFin (see Figure 8). For large amplitude signals (standard

CMOS logic levels), dc coupling may be used.

Use of the On–Chip Oscillator Circuitry

The on–chip amplifier (a digital inverter) along with an ap-

propriate crystal may be used to provide a reference source

frequency. A fundamental mode crystal, parallel resonant at

MOTOROLA

the desired operating frequency, should be connected as

shown in Figure 19.

The crystal should be specified for a loading capacitance

(CL) which does not exceed approximately 20 pF when used

at the highest operating frequency of 15 MHz. Assuming

R1 = 0 Ω, the shunt load capacitance (CL ) presented across

the crystal can be estimated to be:

CL = CinCout + Ca + Cstray + C1 • C2

Cin+Cout

C1 + C2

where

Cin = 5 pF (see Figure 20)

Cout = 6 pF (see Figure 20)

Ca = 1 pF (see Figure 20)

C1 and C2 = external capacitors (see Figure 19)

Cstray = the total equivalent external circuit stray capaci–

tance appearing across the crystal terminals

The oscillator can be “trimmed” on–frequency by making a

portion or all of C1 variable. The crystal and associated com-

ponents must be located as close as possible to the REFin

and REFout pins to minimize distortion, stray capacitance,

stray inductance, and startup stabilization time. Circuit stray

capacitance can also be handled by adding the appropriate

stray value to the values for Cin and Cout. For this approach,

the term Cstray becomes 0 in the above expression for CL.

Power is dissipated in the effective series resistance of the

crystal, Re, in Figure 21. The maximum drive level specified

by the crystal manufacturer represents the maximum stress

that the crystal can withstand without damage or excessive

shift in operating frequency. R1 in Figure 19 limits the drive

level. The use of R1 is not necessary in most cases.

To verify that the maximum dc supply voltage does not

cause the crystal to be overdriven, monitor the output

MC145190•MC145191

17

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