TH71221 datasheet(23/44 Pages) MELEXIS

23 / 44 page

TH71221

27 to 930MHz

FSK/FM/ASK Transceiver

39010 071221

Page 23 of 44

Data Sheet

Rev. 005

June/07

5.1.3

B – word

Name

Bits

Description

Reference divider ratio in TX operation mode

[9:0]

4d .. 1023d

Set the desired steady state current of the reference oscillator

ROMIN

[12:10]

000

001

010

011

100

101

110

111

μA

150

μA

225

μA

300

μA

375

μA

450

μA

525

μA

#default

The control circuitry regulates the current of the oscillator core

between the values ROMAX and ROMIN. As the regulation input

signal the amplitude on pin RO is used. If the ROMIN value is

sufficient to achieve an amplitude of about 400mV on pin RO the

current of the reference oscillator core will be set to ROMIN.

Otherwise the current will be permanently regulated between

ROMAX and ROMIN. If ROMIN and ROMAX are equal no

regulation of the oscillator current occurs. Please also note the

block description of the reference oscillator in para. 3.1.1

Set the start-up current of the reference oscillator

ROMAX

[15:13]

000

001

010

011

100

101

110

111

μA

150

μA

225

μA

300

μA

375

μA

450

μA

525

μA #default

Set the start-up current of the reference oscillator core. Please

also note the description of the ROMIN register and the block

description of the reference oscillator which can be seen above.

OA2 operation

disabled

enabled

#default

OA2

[16]

OA2 can be enabled in FSK receive mode. OA2 is disabled in ASK mode receive.

Internal AFC feature

disabled

enabled

#default

AFC

[17]

Hysteresis on pin GAIN_LNA

LNAHYST

[18]

disabled

enabled

#default

Delayed start of the PLL

undelayed start

PLL starts at the reference oscillator start-up

starts after 8 valid RO-cycles

#default

DELPLL

[19]

PLL starts after 8 valid RO-cycles before entering an active mode to ensure reliable oscillation

of the reference oscillator.

not used

[20]

set to ‘1’ for correct function

RSSI Peak Detector

disabled

#default

The RSSI output signal directly feeds the data slicer setup by means of OA1.

enabled

PKDET

[21]

In ASK receive mode the RSSI Peak Detector output is multiplexed to pin INT2/PDO.

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