MICRF506BML datasheet(22/28 Pages) MICREL

22 / 28 page

Micrel

MICRF506

September 2004

M9999-092904

(408) 955-1690

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

Word A

Word B

000

1011

0100

001

1100

010

0011

011

1010

100

0101

101

1001

110

0110

111

1101

0010

Table 13. 3B4B Encoding

Data bits

Encoded words

Comments

000 000 000 000 000

1011 0100 1011 0100 1011

A Flag indicates if “Word

A” has been used

111 111 010 110 000

1101 0010 0011 0110 1011

A Flag indicates if “Word

A” has been used

Table 14. Example of 3B4B encoding

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

PIN 29, VAR_IN

Figure 16.

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

deviation.

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.

Drift of carrrier in openloop modulation (Hz/ms)

Vdd=2.5V

-40

-20

204060

100

Temperature (deg C)

Figure 17. Open loop leakage

Deviation

-120

-100

-80

-60

-40

-20

100

200

300

400

500

600

700

800

900

Peak-to-peak deviation [kHz]

MOD_A=0

MOD_A=1

MOD_A=2

Figure 18. Open loop, frequency offset

MICRF506BML датащи(PDF) 22 Page - Micrel Semiconductor

MICRF506BML датащи(HTML) 22 Page - Micrel Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

датащи скачать

ссылки URL