SX1211I084TRT(2007) Просмотр технического описания (PDF) - Semtech Corporation

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SX1211I084TRT
(Rev.:2007)

Lowest Power Integrated UHF Transceiver Short Range Devices

Semtech Corporation 

ADVANCED COMMUNICATIONS & SENSING

SX1211

Again, fc as a function of RXParam_ButterFilt is given in the section 3.4.6.

N.B. In the specific case where the frequency of the companion transmitter is not well controlled (i.e. it can drift by

more than +/-100kHz), the user can artificially set the fo to a higher value (such as 150kHz), and increase the filter

bandwidth. This, of course, leads to a concomitant decrease in sensitivity.

3.4.5. Channel Filters Setting in FSK Mode

Fc, the 3dB cutoff frequency of the Butterworth filter used in FSK reception, is programmed through the bit

RXParam_ButterFilt. However, the whole receiver chain influences this cutoff frequency. Thus the channel select

and resultant filter bandwidths are summarized in the following chart:

Theoretical

BW (kHz)

Actual

BW (kHz)

450

400

350

300

250

200

150

100

50

0

0

2

4

6

8

10

12

14

16

Va l(RXPa ra m _Butte rFilt)

Figure 19: Butterworth Filter's Actual BW

3.4.6. Channel Filters Setting in OOK Mode

The center frequency, fo, is always set to 100kHz. The following chart shows the receiver bandwidth when

changing RXParam_Butterfilt bits, while the polyphase filter is activated.

Theoretical BW=fc-fo

Actual

BW (kHz)

450

400

350

300

250

200

150

100

50

0

0

2

4

6

8

10

12

14

16

Va l(RX Pa ra m _Butte rFi lt)

RXPa ra m _PolypFilt="0011"

Figure 20: Polyphase Filter's Actual BW

3.4.7. RSSI

3.4.7.1. General Description

After filtering, the I and Q signals are amplified by a chain of 11 amplifiers, each with 6 dB gain. The outputs of

these amplifiers are used to evaluate the Received Signal Strength (RSSI). A limiting amplifier is located after the I

V3.0 – august 15th, 2007

Page 27 of 73

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