MICRF507 datasheet(15/47 Pages) MICREL

15 / 47 page

Micrel, Inc.

MICRF507

October 2, 2013

Revision 2.2

Clock Generation

The MICRF507’s crystal oscillator:

•

Serves as the reference for the synthesizer that is

the carrier and local oscillator source.

•

Is divided down to clock the switched-capacitor IF

filter.

•

Is divided down to generate three other clocks: bit

rate

clock,

bit

synchronization

clock,

and

modulator clock

Figure 6 shows the oscillator with its frequency-shifting

capacitor bank (controlled by the register field XCOtune)

and the frequency dividers that derive the latter three

clocks from its output. This division occurs in two stages.

First, the XCO output is divided by the 6-bit field Refclk_K,

which has allowable values between 1 and 63. Then, for

each of the three clocks, another field (BitSync_clkS,

BitRate_ClkS, and ModClkS, respectively) selects the

number of further divisions by 2. Complete relationships of

field values and resultant frequencies are given below for

each clock.

Field Name

Number

of bits

Location

of bits

Description

XCOtune

Reg9[4:0]

Crystal oscillator trimming.

RefClk_K

Reg7[5:0]

Reference clock divider.

BitRate_clkS

Reg6[0],

Reg7[7:6]

Transmitter Bit rate clock setting. See Figure 9 and “Data

Interface and Bit Synchronization” section for more details.

Mod_clkS

Reg6[6:4]

VCO Modulator clock setting, set the modulator clock to

either 8x or 16x the bit rate clock.

BitSync_clkS

Reg6[3:1]

Receiver Bit Synchronization clock setting, always set bit

synchronization clock to 16x the bit rate clock. See Figure 9

and “Data Interface and Bit Synchronization” section for more

details.

Table 3. Register Bit Fields for Clock Generation

Figure 6. MICRF507 Clock Sources

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