MICRF507 datasheet(32/46 Pages) MICREL

32 / 46 page

Micrel, Inc.

MICRF507

March 2010

M9999-032210-B

Figure 22 shows two waveforms with different attenuator

setting:

Mod_Ab

Mod_Aa

. If Mod_A is increased, the

frequency deviation is lowered and vice versa.

The resulting frequency deviation in terms of the

parameters discussed above is given in the following

equations:

Mod_clkS)

XCO

MOD_CLK

Refclk_K

−

()

MOD_CLK

DEV

Mod_A

Mod_I

where:

fDEV:

Single sided frequency deviation [Hz]

fXCO:

Crystal oscillator frequency [Hz]

fRF:

Center frequency [Hz]

Refclk_K:

6 bit divider, values between 1 and 63

Mod_clkS:

Modulator

clock

setting,

values

between 0 and 7

fMOD_CLK:

Modulator clock frequency, derived

from the crystal frequency, Refclk_K

and Mod_clkS

Mod_I:

Modulator

current

setting,

values

between 0 and 31

Mod_A:

Modulator attenuator setting, values

between 0 and 15

C1:

-2.72 x 10

C2:

85.2

Note that the constants C1 and C2 are empirically derived.

Actual frequency deviation may differ by a few percent.

Modulator Filter

To reduce the high-frequency components in the

generated waveform, a filter with programmable cut-off

frequency can be enabled. This is done using Mod_F[2:0],

bit 0 being LSB. The Mod_F field should be set according

to the formula:

bps

150x10

Mod_F

Figure 23. Modulator Waveform with and without Filtering

in which rb is the bit rate in bits/sec. Mod_F=0 disables the

modulator filter and Mod_F=7 provides the most filtering.

Figure 23 shows a waveform with and without the filter.

The modulator filter will not influence the frequency

deviation as long as the programmed cut-off frequency is

above the actual bit rate.

MICRF507 Datasheet(PDF) 32 Page - Micrel Semiconductor

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