MICRF405 datasheet(20/46 Pages) MICREL

20 / 46 page

Micrel

MICRF405

April 2006

M9999-041906

(408) 955-1690

The frequency synthesizer consists of a voltage-

controlled

oscillator

(VCO),

crystal

oscillator,

prescaler, programmable frequency dividers, phase-

detector and charge pumps. Two different types of

prescalers are integrated, a pulse swallow and a

phase select prescaler. The recommended prescaler

is the phase select prescaler (Prescaler_Sel=0,

which is default). There is both a configurable on-

chip loop filter and an external loop filter. The

lengths of the N and M and A registers are 12, 12

and 6 bits respectively. The M, N and A values can

be calculated from the formula:

Phase select prescaler (Prescaler_Sel=0):

)

(

XCO

⋅

Pulse swallow prescaler (Prescaler_Sel=1):

)

(

XCO

⋅

where:

fXCO: Crystal oscillator frequency

fRF: RF frequency

0 < A ≤ N

k: 6: RF frequency 290-325 MHz,

Freq_Band[1:0]=0

4: RF frequency 430-490 MHz,

Freq_Band[1:0]=1

2: RF frequency 860-980 MHz,

Freq_Band[1:0]=2-3

There are two sets of each of the divide factors (i.e.

A0 and A1). If modulation by using the dividers is

selected Modulation1=1, Modulation0=0), the two

sets should be programmed to give two RF

frequencies, separated by two times the specified

single sided frequency deviation. For all other

modulation methods, the 0-set will be used. The

value of A is constrained to be less or equal to N,

0<=A<=N.

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