WE2408 View Datasheet(PDF) - Unspecified
Part Name
Description
MFG CO.
'WE2408' PDF : 36 Pages View PDF
WiNEDGE & WiRELESS
Winceiver WE2408
2.4GHz Single Chip FM Transceiver
IF FILTER BANDWIDTH
The bandwidth of the on-chip IF low pass filter, which precedes the Period to Digital demodulator,
should be optimized as follows. Following the calculation of Fif and BWdm from section above, the
filter bandwidth is adjusted by choice of the external resistor between VDDA and IFSET.
R = 22kΩ x 206kHz / (Fif + 0.5 x BWdm)
There is an on-chip high pass IF filter fixed at 8kHz.
Examples of BW and corresponding IFSET value
Common
Rx BW
150 kHz
100 kHz
50 kHz
25 kHz
BWbb
75 kHz
50 kHz
25 kHz
12.5 kHz
PDR
9
12
24
48
Fif
163 kHz
123 kHz
61.3 kHz
30.6 kHz
BWdm
153 kHz
115 kHz
57 kHz
29 kHz
IFSET
R
18 kΩ
24 kΩ
51 kΩ
100 kΩ
RSSI
The RSSI circuit works with external shunt capacitor (10nF) to develop a filtered voltage level
inversely proportional to the receive RF signal strength.
The RSSI measurement range is from -100dBm to -35dBm, with the RF input pad bypassed (0dB)
and the quadrature mixer gain stage set to high. This range is extended as the receiver gain is
reduced. The RSSI conversion factor is # (-30mV/dB), with a voltage range of 2.1 to 0.1 Vdc.
RSSI TOLERANCE
For WE2408 alone, the RSSI tolerance is +/-2%.
If external low noise amplifier (LNA) and filters are added at the Rx front end, the LNA gain and filter
loss will vary from unit to unit and will contribute to additional RSSI variation above the IC’s RSSI
tolerance.
As the RSSI voltage depends on its load, it should be connected only to an ADC or a comparator with
high input impedance.
METHODS OF CORRECTING RSSI TOLERANCE
For applications that require accurate RSSI, the tolerance can be corrected by the use of an analog-
to-digital converter (ADC) or a trimmer pot meter.
If ADC is used, the tolerance can be corrected using software.
If non-volatile memory (EEPROM or flash) is available, correction can be done during production
testing. The ADC can read RSSI values at no signal and at a know Rx signal level, and store those
values to correct for the RSSI tolerance.
© 2003 WiNEDGE & WiRELESS PTE LTD
Rev Date: 2003 May 23
Page 17
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