CC400-RTR2 datasheet(21/31 Pages) TI

21 / 31 page

CC400

SWRS050

Page 21 of 32

27.

Demodulator Precharging For Reduced Turn-on Time

The demodulator data slicer has an

internal AC coupling giving a time constant

of approximately 30 periods of the bit rate

period. This means that before proper

demodulation can take place, a minimum

of 30 start-bits has to be received.

In critical applications where the start-up

time should be decreased in order to

reduce the power consumption, this time

constant can be reduced to 5 periods

using the optional precharging possibility.

The precharging is done during data

reception by setting the precharging bit in

the configuration register active with

duration of at least 5 bit periods.

Data received

without

precharging

PRECHARGE

Time

Data

transmitted

5 bit periods

Data valid

Data not valid

Data valid

Data not valid

5 bit periodes

30 bit periodes

Data received with

precharging

Figure 12: Demodulation using precharging.

In the example shown in Figure 12, data is

transmitted

continuously

from

the

transmitter (all 1’s). At t=t1 the receiver is

turned on, and then the precharging is

kept on for about 5 bit periods. At t=t2 the

received data is valid and precharging is

turned off. When not using precharging,

data is not valid until 30 bit periods, at t=t3.

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