MICRF505BML datasheet(22/27 Pages) MICREL

22 / 27 page

MICRF505

Micrel

M9999-051304

May 13, 2004

Frequency Modulation

A6..A0

0000001

Modulation1 Modulation0

‘0’

PA_LDc_en

RSSI_en

LD_en

PF_FC1

PF_FC0

Modulation1

Modulation0

Modulation Type

Closed loop modulation

using modulator

Not in use

FSK applied using two

sets of dividers

Not in use

Table 11. Modulation Bit Setting

When Modulation1 and Modulation0 is 00, the modulator

needs to be programmed properly, see “Modulator” section.

The modulation signal will now be applied directly on the

phase locked VCO. It is therefore important that the PLL

bandwidth is not too high, as this will remove the modulation.

See “PLL Filter” section on how to calculate the PLL compo-

nents. When using the modulator the modulation signal is

applied to the VCO and therefore some sort of encoding is

needed.

The level of encoding is determined by the PLL loop filter

bandwidth and data rate. Two of the most common encoding

techniques are Manchester encoding and 3B4B. Other en-

coding schemes may also be used.

Manchester encoding is when one bit is encoded in to a two-

bit word and is shown in Table 10. When using Manchester

encoding the maximum overhead is 100%. When selecting

PLL loop filter it is important to note that the min baud rate is

equal to:

baud / s

baud_min

fbaud_min: The minimum frequency of the baud rate (Hz)

baud/s: Elements per second (encoded data)

Data

Word

“0”

“10”

“1”

“01”

Table 12. Manchester Encoding

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 modu-

lated 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 Enconding

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

MICRF505BML датащи(PDF) 22 Page - Micrel Semiconductor

MICRF505BML 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

датащи скачать

ссылки URL