RFRXD0420 Datasheet, PDF (10/32 Pages) Microchip Technology – UHF ASK/FSK/FM Receiver

rfRXD0420/0920
FIGURE 3-3: FREQUENCY PLANNING WORKSHEET
Step 1: Identify receive (f_rf) and IF frequency (f_if).
f_rf =
____________________
f_rf
f_if
f_lo
f_if =
____________________
Step 2: Calculate crystal frequencies for high- and low-side injection:
High-side Injection
f_XTAL x PLL divide ratio
f_XTAL-HIGH =
( ) f_rf + f_if
PLL divide ratio
( ) _________ + _________
=
= _______________
16 if rfRXD0420
32 if rfRXD0920
Low-side Injection
f_XTAL-LOW =
( ) f_rf - f_if
PLL divide ratio
( ) _________ - _________
=
= _______________
16 if rfRXD0420
32 if rfRXD0920
Step 3: Calculate Local Oscillator (LO) frequencies (f_lo) using f_XTAL-HIGH and f_XTAL-LOW:
High-side Injection
16 if rfRXD0420
f_lo-HIGH = f_XTAL-HIGH x PLL Divide Ratio =
_________ x
= _____________
32 if rfRXD0920
Low-side Injection
16 if rfRXD0420
f_lo-LOW =
f_XTAL-LOW x PLL Divide Ratio =
_________ x
= _____________
32 if rfRXD0920
Step 4: Select high-side injection (f_lo-HIGH) or low-side injection (f_lo-LOW) that corresponds to the LO frequency
that is between the ranges of:
Device
rfRXD0420
rfRXD0920
LO Frequency Range
300 to 430 MHz
800 to 915 MHz
Step 5: From the chosen injection mode in Step 4, write the selected crystal frequency (f_XTAL) and circle
injection mode.
f_XTAL =
____________________
(circle one)
High-side Injection Low-side Injection
Step 6: Calculate image frequency (f_rf-image) for the Injection mode chosen:
if High-side Injection
f_rf-image = f_rf + (2 x f_if)
if Low-side Injection
= ___________ + ( 2 x ___________ ) = ______________
f_rf-image = f_rf - (2 x f_if) = ___________ - ( 2 x ___________ ) = ______________
Note: Image frequency should be sufficiently filtered by the preselector for the application.
DS70090A-page 10
Preliminary
 2003 Microchip Technology Inc.