SM1211E915TOPIC Semtech, SM1211E915TOPIC Datasheet - Page 16

• Manufacturer Part Number: SM1211E915TOPIC
• Description: KIT PICTAIL EXT FOR SX1211
• Manufacturer: Semtech
• Type: Transceiver, UHFr

Specifications of SM1211E915TOPIC

• Frequency: 915MHz
• For Use With/related Products: SX1211
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Note for mass production: The VCO capacitance is piece to piece dependant. As such, the optimization proposed
above should be verified on several prototypes, to ensure that the population is centered on 100 mV.
To adequately reject spurious components arising from the comparison frequency Fcomp, an external 2
loop filter is employed.
Following the recommendations made in section 3.2.4, the loop filter proposed in the reference design’s bill of
material on section 7.5.3 should be used. The loop filter settings are frequency band independent and are hence
relevant to all implementations of the SX1211.
The SX1211 also features a PLL lock detect indicator. This is useful for optimizing power consumption, by adjusting
the synthesizer wake up time (TS_FS), since the PLL startup time is lower than specified under nominal conditions.
The lock status can be read on bit IRQParam_PLL_lock, and must be cleared by writing a “1” to this same register.
In addition, the lock status can be reflected in pin 23 PLL_LOCK, by setting the bit IRQParam_Enable_lock_detect.
As shown in Figure 5 the PLL structure comprises three different dividers, R, P and S, which set the output
frequency through the LO. A second set of dividers is also available to allow rapid switching between a pair of
frequencies: R1/P1/S1 and R2/P2/S2. These six dividers are programmed by six bytes of the register MCParam
from addresses 6 to 11.
The following formula gives the relationship between the local oscillator, and R, P and S values, when using FSK
modulation.
Due to the manner in which the baseband OOK symbols are generated, the signal is always offset by the FSK
frequency deviation (Fdev - as programmed in MCParam_Freq_dev). Hence, the center of the transmitted OOK
signal is:
Rev 7 – Sept 2
ADVANCED COMMUNICATIONS & SENSING
3.2.6. PLL Loop Filter
3.2.7. PLL Lock Detection Indicator
3.2.8. Frequency Calculation
nd
, 2008
3.2.8.1. FSK Mode
3.2.8.2. OOK Mode
CL2
Frf
Frf
,
,
fsk
fsk
Figure 7: Loop Filter
RL1
9
8
9
8
CL1
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Fxtal
R
1
75
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S
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SX1211
nd
order