MLX71122_16 datasheet(19/59 Pages) MELEXIS

19 / 59 page

MLX71122

300 to 930MHz FSK/FM/ASK Receiver

Datasheet

REVISION 014 – AUGUST, 2016

Page 19 of 59

390 10 71122 01

3.1.2. Calculation of LO1 and IF1 frequency for Low Frequency Bands

High-high or high-low injection can be used for the low frequency bands. If equal channel steps are desired,

choose a PFD frequency fPFD according to the table below. The R counter values are valid for a 10MHz

crystal reference frequency fRO. The PFD frequency is given by fPFD = fRO /R.

Injection Type

fCH [kHz]

fPFD [kHz]

h-h

13.3

750

h-h

12.5

16.7

600

h-h

26.7

375

h-h

33.3

300

h-h

66.7

150

h-h

100

133.3

h-h

250

333.3

The second step is to calculate the missing parameters fLO1, fIF1, Ntot, N and A. While the second IF (fIF2), the

NLO2 divider ratio and the prescaler divider ratio P are bound to fIF2 = 2MHz, NLO2 = 4 (or 8) and P =32.

)

IF2

LO2

LO1





2MHz)

LO1





(10)

LO2

IF2

LO2

IF1





8MHz

IF1





(11)

Finally N and A can be calculated with equation (6).

3.1.3. Calculation of LO1 and IF1 frequency for High Frequency Bands

Typical ISM band operating frequencies like 868.3 and 915MHz can be covered without changing the

crystal or the VCO inductor. Low-low injection is usually used for the high frequency bands. If equal

channel steps are desired, choose a PFD frequency fPFD according to the table below. The R counter values

are valid for a 10MHz crystal reference. The PFD frequency is given by fPFD = fRO /R.

Injection Type

fCH [kHz]

fPFD [kHz]

l-l

625

l-l

500

l-l

250

l-l

100

125

l-l

250

200

l-l

500

400

The second step is to calculate the missing parameters fLO1, fIF1, Ntot, N and A. While the second IF (fIF2), the

NLO2 divider ratio and the prescaler divider ratio P are bound to fIF2 = 2MHz, NLo2 = 4 (or 8) and P =32.

)

IF2

LO2

LO1







2MHz)

LO1





(12)

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