MRF39RA datasheet(21/72 Pages) MICROCHIP

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 2015 Microchip Technology Inc.

DS40001778B-page 21

MRF39RA

3.2.1

RECEIVER START-UP TIME

It is highly recommended to use the built-in sequencer

of the MRF39RA to optimize the delays when setting

the chip in Receive mode. It ensures the shortest start-

up times, hence the lowest possible energy usage for

battery-operated systems.

The start-up times of the receiver can be calculated as

shown in Figure 3-1 through Figure 3-3.

FIGURE 3-1:

Rx START-UP – NO AGC, NO AFC

FIGURE 3-2:

Rx START-UP – AGC, NO AFC

FIGURE 3-3:

Rx START-UP – AGC AND AFC

The different timings shown above are as follows:

• Group delay of the analog front end: Tana = 20 µs

• Channel filter’s group delay in FSK mode:

Tcf = 21/(4.RxBw)

• Channel filter’s group delay in OOK mode:

Tcf = 34/(4.RxBw)

• DC Cutoff’s group delay: Tdcc = max(8,

2^(round(log2(8.RxBw.Tbit)+1))/(4.RxBw)

• PLL lock time after AFC adjustment: Tpllafc = 5/

PLLBW (PLLBW = 300 kHz)

• AFC sample time: Tafc = 4 x Tbit (also denoted

TS_AFC in the general specification)

• RSSI sample time: Trssi = 2 x int(4.RxBw.Tbit)/

(4.RxBw) (also known as TS_RSSI).

Analog FE’s

group delay

Channel Filter’s

group delay

DC Cutoff’s

group delay

RSSI

sampling

XO Started and PLL is locked

Tana

RSSI

sampling

Tcf

Tdcc

Trssi

Reception of Packet

ModeReady

RxReady

TS_RE

Rx startup request

(sequencer or user)

Received Packet Preamble may start

Analog FE’s

group delay

Channel Filter’s

group delay

DC Cutoff’s

group delay

RSSI

sampling

XO Started and PLL is locked

Tana

RSSI

sampling

Tcf

Tdcc

Trssi

Reception of Packet

ModeReady

RxReady

Channel Filter’s

group delay

DC Cutoff’s

group delay

RSSI

sampling

Tcf

Tdcc

Trssi

The LNA gain is adjusted by

the AGC, according to the

RSSI result

TS_RE_AGC

Rx startup request

(sequencer or user)

Received Packet Preamble may start

Analog FE’s

group delay

Channel Filter’s

group delay

DC Cutoff’s

group delay

RSSI

sampling

XO Started and

PLL is locked

Tana

RSSI

sampling

Tcf

Tdcc

Trssi

Reception of Packet

ModeReady

RxReady

Channel Filter’s

group delay

DC Cutoff’s

group delay

RSSI

sampling

Tcf

Tdcc

Trssi

AFC

Tafc

PLL

lock

Tpllafc

Channel Filter’s

group delay

Tcf

DC Cutoff’s

group delay

Tdcc

TS_RE_AGC&AFC

Rx startup request

(sequencer or user)

The LNA gain is adjusted by

the AGC, according to the

RSSI result

Carrier Frequency is adjusted

by the AFC

Received Packet Preamble may start

Note:

The timings represent maximum settling

times. Shorter settling times may be

observed in real cases.

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