MICRF506BML Micrel Inc, MICRF506BML Datasheet - Page 27

• Manufacturer Part Number: MICRF506BML
• Manufacturer: Micrel Inc

Specifications of MICRF506BML

• Operating Frequency (max): 450000kHz
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Modulation Type: FSK
• Lead Free Status / Rohs Status: Not Compliant

Modulator Attenuator
A third way to set the deviation is by programming
the modulator attenuator, Mod_A2..Mod_A0, the last
being LSB. The purpose of the attenuator is to allow
small deviations when the bit rate is small and/or the
BT is small (these settings will give a relatively slow
modulator clock, and therefore long rise- and fall
times, which in turn results in large frequency
deviations). In addition, the attenuator will improve
the resolution in the modulator.
The effect of the attenuator is given by:
Figure 22 shows two waveforms with different
attenuator setting:
is increased, the frequency deviation is lowered and
vice versa.
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_F2..Mod_F0, the least one being LSB. The
Mod_F should be set according to the formula:
July 2006
Figure 21. Two Different Modulator Current Settings
Figure 22. Two Different Modulator Attenuator
Mod_Ab > Mod_Ab
Mod_la > Mod_lb
Mod_la
Mod_lb
Mod_Aa
Mod_Ab
f
DEVIATION
M o d _ A a
Settings
×
1+ Mod_A
<
1
M o d _ A b
. If Mod_A
27
Mod_F=0 disables the modulator filter and Mod_F=7
gives most filtering. Figure 22 shows a waveform
with and without the filter.
Calculation of the Frequency Deviation
The parameters influencing the frequency deviation
can be summarized in the following equations:
Where:
Figure 23. Modulator Waveform with and without
f
f
f
Refclk_K:
Mod_clkS:
f
Mod_I:
Mod_A:
C1:
C2:
DEV
XCO
RF
MOD_CLK
f
DEV
:
:
:
f
Mod_filter off
=
MOD_CLK
f
MOD_CLK
Mod_I
:
=
Single sided frequency deviation
[Hz]
Crystal oscillator frequency [Hz]
Center frequency [Hz]
6 bit divider, values between 1
and 63
Modulator clock setting, values
between 0 and 7
Modulator
derived
frequency,
Mod_clkS
Modulator
values between 0 and 31
Modulator
values between 0 and 15
-2.17·10
82
×
Refclk_K × 2
1+ Mod_A
Filtering
Mod_filter on
1
10
f
XCO
from
× C
(7−Mod_clkS )
attenuator
(
clock
current
Refclk_K
1
[phone]
+ C
M9999-092904
the
2
× f
frequency,
RF
)
setting,
setting,
crystal
and