XE1202 Datasheet, PDF (8/26 Pages) List of Unclassifed Manufacturers – Low-power, integrated UHF transceiver

Data Sheet
XE1202
4.1 Detailed description
4.1.1 Receiver
The outputs of the receiver are the two signals DATAOUT and DCLK. When the bit “RTParam_Bits” is “1” (see the
Configuration register section below), the bit synchronizer is turned on, and the two output signals are respectively
the output NRZ bit stream and the sampling clock. The function of the bit synchronizer is to remove the glitches
from the bit stream DATAOUT and to provide the output clock DCLK. The value of DATAOUT is valid at the rising
edge of DCLK.
For proper behavior of the bit synchronizer, three conditions must be satisfied:
- the received data must start with a preamble of 24 bits for synchronization; this preamble must be a
sequence of “0” and “1” sent alternatively,
- after that, the incoming bit stream must have at least one transition from “0” to “1” or from “1” to “0”
every 8 bits,
- the accuracy of the bit rate must be better than ± 5 % (assuming the reference Xtal oscillator is exactly
39 MHz)
When “RTParam_Bits” is “0”, the bit synchronizer is turned off, and the signal DATAOUT is the output of the
demodulator. In this case DCLK is not used and its value is set to “low”.
The condition on the modulation index for proper behavior of the demodulator is:
β
=
2⋅∆f
BR
≥ 2,
where ∆f is the frequency deviation and BR the bit rate.
4.1.2 High sensitivity vs. high linearity: A-mode, B-mode
The receiver can be operated in two different modes that provide the highest sensitivity or the highest linearity. This
is programmable with the register “RTParam_Rmode” (see the Configuration register section below).
- A-mode: the receiver has the highest sensitivity (see RFS parameter)
- B-mode: the receiver has the highest linearity (see IIP3 parameter)
4.1.3 RSSI
When activated, this function provides a Received Signal Strength Indication based on the signal at the output of
the base-band filter. To activate this function, the bit “RTParam_RSSI” (see the Configuration register section
below) must be set “1”. When activated, the status is a 2-bits data stored in register “DataOut_RSSI”, which can be
read through the serial control interface. The meaning of this status information is given in the table below, where
V_RFFIL is the differential amplitude of the equivalent input RF signal when the receiver is operated in A-mode. The
thresholds VTHRi are the thresholds at the output of the base-band filter divided by the gain between the input of
the receiver and this output.
DataOut_RSSI
Description
00
V_RFFIL ≤ VTHR1
01
VTHR1 < V_RFFIL ≤ VTHR2
10
VTHR2 < V_RFFIL ≤ VTHR3
11
VTHR3 < V_RFFIL
Table 1 RSSI status description
Two ranges with three VTHRi are defined and selected with the flag “RTParam_RSSR”.
The time diagram of an RSSI measurement is given in the next figure. When the RSSI function has been activated
the signal strength is periodically measured and the result is stored in the register “DataOut_RSSI” at each rising
edge of the DATAIN. TS_RS is the wake-up time required after the function has been activated to get a valid result.
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