MICRF505YML Micrel Inc, MICRF505YML Datasheet - Page 24

• Manufacturer Part Number: MICRF505YML
• Description: 433/915MHZ ITRANSCEIVER, SMD, MLF32
• Manufacturer: Micrel Inc

Specifications of MICRF505YML

• Transmitting Current: 28mA
• Data Rate: 200Kbps
• Frequency Range: 850MHz To 950MHz
• Modulation Type: FSK
• Sensitivity Dbm: -111dBm
• Rf Ic Case Style: MLF
• No. Of Pins: 32
• Supply Voltage Range: 2V To 2.5V
• Output Power: 10dBm
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

MICRF505
Modulator Current
The current used during the rise- and fall times can be
programmed with the Mod_I4..Mod_I0 bit, the last one being
LSB. Figure 15 shows two waveforms generated with two
different currents, where Mod_Ia > Mod_Ib. Higher current
will give a higher frequency deviation and vice versa. The
effect of modulator clock and MOD_1 is illustrated by
To avoid saturation in the modulator it it important not to
exceed maximum Mod_I. Max Mod_I for a given fMOD_clk is
given by:
where min() returns the value of the smallest argument and
int() returns the integer part of the argument.
where int(x): integer and and f_MOD_CLK: Modulater clk
frequency.
Modulator Attenuator
A third way to set the deviation is by programming the
modulator attenuator, Mod_A2..Mod_A0, the last being LSB.
The purposes 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 reso-
lution in the modulator.
The attenuation is given by:
M9999-051304
Figure 18. Two different modulator attenuator settings
Figure 17. Two Different Modulator Current Settings
Mod_Ab > Mod_Ab
Mod_la > Mod_lb
MOD_Imax INT(f_MOD_CLK 28e - 6) -1
Mod_la
Mod_lb
Mod_Aa
Mod_Ab
f
DEVIATION
V
MOD2
a
a
=
MOD_1
1 MOD_A
f
MOD_CLK
+
1
◊
24
where V
and before the attenuator, respectively. Figure 16 shows two
waveforms with different attenuator setting; Mod_Aa <
Mod_Ab. If Mod_A 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 last
one being LSB. The Mod_F should be set according to the
formula:
Mod_F=0 disables the modulator filter and Mod_F=7 gives
most filtering. Figure 18 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 19. Modulator Waveform with and Without
f
f
f
Refclk_K:
Mod_clkS:
f
Mod_I:
Mod_A:
MOD_F
f
DEV
XCO
RF
MOD_CLK
MOD_CLK
f
DEV
MOD2
:
:
Mod_filter off
:
=
MOD_I
f
MOD_CLK
and V
=
=
:
150 10
Refclk_K 2
BitRate
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 clock frequency, derived
from the crystal frequency, Refclk_K
and Mod_clkS
Modulator current setting, values
between 0 and 31
Modulator attenuator setting, values
between 0 and 15
◊
¥
1 MOD_A
MOD1
+
3
Mod_filter on
Filtering
1
¥
is the modulator amplitude after
f
XCO
(
7 Mod clkS
¥
◊ -
(
44 28 10 72
_
.
)
◊
9
May 13, 2004
◊
f
RF
)
Micrel