Si4420

28

RX-TX ALIGNMENT PROCEDURES

RX-TX frequency offset can be caused only by the differences in the actual reference frequency. To minimize these errors it is suggested to

use the same crystal type and the same PCB layout for the crystal placement on the RX and TX PCBs.

To verify the possible RX-TX offset it is suggested to measure the CLK output of both chips with a high level of accuracy. Do not measure the

output at the XTL pin since the measurement process itself will change the reference frequency. Since the carrier frequencies are derived

from the reference frequency, having identical reference frequencies and nominal frequency settings at the TX and RX side there should be

no offset if the CLK signals have identical frequencies.

It is possible to monitor the actual RX-TX offset using the AFC status report included in the status byte of the receiver. By reading out the

status byte from the receiver the actual measured offset frequency will be reported. In order to get accurate values the AFC has to be

disabled during the read by clearing the "en" bit in the AFC Control Command (bit 0).

TYPICAL APPLICATIONS

Repeater Demo (915 MHz)

Schematics

6V

3,3V

P0.0

2

P0.1

1

P0.2

28

P0.3

27

P0.4

26

P0.5

25

P0.6

24

P0.7

23

P1.0

22

P1.1

21

P1.2

20

P1.3

19

P1.4

18

P1.5

17

P1.6

16

P1.7

15

P2.0

14

P2.1

13

P2.2

12

P2.3

11

P2.4

10

P2.5

9

P2.6

8

P2.7

7

P3.0/C2D

6

/RST/C2CK

5

VDD

4

GND

3

IC1

5

3

4

1

SW1

6

R3

R4

R5

R6

C1

2

1

SJ1

R7

1

2

3

J1

1

2

3

DEBUG

C2

Q1

1

2

34

5

IC3

GND

IN

ON

OUT

POK

C3

C4

1

2

BATTERY

C5

C6

C7

X1

SDI

1

SCK

2

NSEL

3

SDO

4

NIRQ

5

FSK/DATA/NFFS

6

DCLK/CFIL

7

NINT/VDI

16

XTL/REF

9

CLK

8

VSS

11

RF2

12

RF1

13

VDD

14

ARSSI

15

NRES

10

IC2

TX

TX

RX

RX

SEL

SEL

CLK

CLK

IRQ

IRQ

SCK

SCK

MISO

MISO

MOSI

MOSI

FFS

FFS

FFE

FFE

INT/VDI

INT/VDI

ARSSI

ARSSI

C8051F311

GND

GND

820

820

820

820

GND

GND

VCC

100nF

GND

GND

1k

4,7nF

10MHz

GND

GND

VCC

GND

IA2112-3.3V

2,2uF

2,2uF

1uF

100pF

10pF

GND

GND

IA4420-REVC