micrf506 Micrel Semiconductor, micrf506 Datasheet - Page 22

• Manufacturer Part Number: micrf506
• Description: 410mhz And 450mhz Ism Band Transceiver
• Manufacturer: Micrel Semiconductor

Another much more efficient encoding type is 3B4B
where three data bits are encoded into a four-bit
word. The reason for encoding is to minimize the dc
component in the modulated data. To have minimum
dc component each four bit word should include two
elements of “1” and two elements of “0”. Following
this guidance only 6 out of 8 word complies and two
encoded words needs special precaution. Whenever
000 and 111 data appear, the user must set/clear a
flag that indicate if last encoded word was “Word A”
and select the respective encoded word shown in
Table 11.
Data bits
000 000 000 000 000
111 111 010 110 000
When modulation is selected (Mode1,Mode0=01),
the output of the charge pump will be tristated if
DataIXO is either high or low. If DataIXO is tristated,
the PLL is active. When the PLL is opened the
varactor voltage will decrease with time due to
leakage and external capacitor is connected to pin
VarIn to minimize it as shown in Figure 16.
PIN 27, CP_OUT
Micrel
September 2004
Data
000
001
010
011
100
101
110
111
Table 14. Example of 3B4B encoding
Table 13. 3B4B Encoding
Encoded words
1011 0100 1011 0100 1011
1101 0010 0011 0110 1011
C1
Figure 16.
Word A
1011
1100
0011
1010
0101
1001
0110
1101
R1
C2
Comments
A Flag indicates if “Word
A” has been used
A Flag indicates if “Word
A” has been used
C3
Word B
0100
0010
PIN 29, VAR_IN
22
The modulation is applied using the modulator
described in chapter Modulator , but since the loop is
open during modulation any kind of encoding is
allowed (NRZ, Manchester, 3B4B etc). It is important
to notice that after end of transmission the DataIxO
should be in last valid logic state before the PA
stage is turned off. This is to avoid spurious
emission. When using open-loop modulation a
deviation offset is present and has to be included in
the total deviation calculation. Figure 18 illustrate the
relationship between the frequency offset and
deviatio
The drift of the carrier over temperature is measured
as shown in Figure 17 . The loop bandwidth is
around 10kHz and the capacitor on the VarIn pin is
68nF X5R.
18
16
14
12
10
8
6
4
2
0
n.
-40
Figure 18. Open loop, frequency offset
-100
-120
-20
-40
-60
-80
20
0
0
Drift of carrrier in openloop modulation (Hz/ms)
Figure 17. Open loop leakage
-20
100
200
MOD_A=0
0
300
Peak-to-peak deviation [kHz]
Temperature (deg C)
Deviation
Vdd=2.5V
20
400
MOD_A=1
500
40
600
MOD_A=2
60
700
[phone]
M9999-092904
800
80
MICRF506
900
100