TDA5251F1 Datasheet, PDF (67/88 Pages) Infineon Technologies AG – ASK/FSK 315MHz Wireless Transceiver

TDA5251 F1
Version 1.0
Confidential
Application
3.7.1 Frequency Window for Data Rate Detection
The high time of data is used to measure the frequency of the data signal. For Manchester coding
either the data frequency or half of the data frequency have to be detected corresponding to one
high time or twice the high time of data signal.
A time period of 3*2*T is necessary to decide about valid or invalid data.
T
2*T
DATA
0
0
1
T2
T1
possible
GATE 1
0
2*T2
2*T1
possible
GATE 2
0
1
t
0
t
t
Figure 3-31 Window Counter timing
Example to calculate the thresholds for a given data rate:
- Data signal manchester coded
- Data Rate: 2kbit//s
- f_clk= 13,125 MHz
Then the period equals to
2 × T = ¹ = 0,5ms
2kbit/s
[3 – 36]
respectively the high time is 0,25ms.
We set the thresholds to +-10% and get: T1= 0,225ms and T2= 0,275ms
The thresholds TH1 and TH2 are calculated with following formulas
TH1 = T1× ^fclk
4
[3 – 37]
window_count_timing.wmf
Preliminary Specification
TH2 = T2 × ^fclk
4
[3 – 38]
67
2003-02-18