MRF49XA-ISLASHT datasheet(61/102 Pages) MICROCHIP

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Preliminary

DS70590C-page 61

MRF49XA

3.14

Power Management

The Power Management Configuration register

enables/disables the following functions:

• Receiver

• Transmitter

• Baseband Circuit

• Synthesizer

• Crystal Oscillator

• Low Battery Detect Circuit

• Wake-up Timer

• Clock Output

Figure 3-12 shows the functions that are enabled using

PMCREG.

Receiver: The RXCEN bit, when set, enables the

entire receiver chain. The receiver chain consists of a

baseband circuit, synthesizer and crystal oscillator.

Transmitter: The TXCEN bit, when set, enables the

entire transmit chain. The transmit chain consists of a

power amplifier, synthesizer, oscillator and transmit

are enabled, any data in the Transmit register is shifted

out and a transmission is started.

Baseband Circuit: The BBCEN bit, when set, enables

the baseband circuit. The baseband circuit, synthesizer

and oscillator work together to demodulate and recover

the data transmitted to the synthesizer (SYNEN bit). If

baseband circuits are enabled, then the oscillator

(OSCEN bit) must be enabled in order to receive data.

The BBCEN bit can be disabled to reduce current

consumption.

Synthesizer: The SYNEN bit, when set, enables the

synthesizer. The synthesizer is comprised of a PLL,

oscillator and VCO for controlling the channel frequency.

This bit must be enabled when either the transmitter or

the receiver is enabled. The oscillator must also be

enabled to provide the reference frequency for the PLL.

On power-up, the synthesizer automatically performs

the calibration. If there are significant changes in voltage

or temperature, recalibration can be performed by

disabling and re-enabling the synthesizer.

Crystal Oscillator: The OSCEN bit, when set, enables

the oscillator circuit. The oscillator provides the

reference signal to the synthesizer when setting the

transmit or receive frequency of use.

Low Battery Detect Circuit: The LBDEN bit, when

set, enables the battery voltage detect circuit. The

battery detector can be programmed to 32 different

threshold levels. See Register 2-16 (BCSREG) for

programming details.

Wake-up Timer: The WUTEN bit, when set, enables

the wake-up timer. See Register 2-14 (WTSREG) for

details on programming the wake-up timer interval.

Clock Output: The CLKOEN bit, when set, disables

the oscillator clock output. On device Reset or

power-up, the clock output is enabled so that a

processor can begin execution of any special setup

sequences as required by the designer. See

The RF front end is comprised of the LNA and the

mixer.

The

synthesizer

block

has

two

main

components: the VCO and the PLL. The baseband

section consists of a baseband amplifier, low-pass

filter, limiter and I/Q demodulator.

The synthesizer also has an internal start-up calibration

procedure. If quick RX/TX switching is needed, leave

this block on. Enabling the transmitter using the

TXCEN bit (PMCREG<5>) will turn on the PA, and

since the synthesizer is already up and running, the PA

immediately produces the TX signal at the output.

To decrease the TX/RX turnaround time, keep the

baseband section on. Switching to Receive mode

means disabling the PA and enabling the RF front end.

Since the baseband block is already on, the internal

start-up calibration is skipped, and thus, the turnaround

time is shorter. The BBCEN, SYNEN and OSCEN bits

are provided to optimize the TX to RX or RX to TX

turnaround time.

The crystal oscillator provides a reference signal to the

RF synthesizer, baseband circuit and digital signal

processor. If the receiver or the transmitter is frequently

used, it is recommended to leave the oscillator running

as the crystal might need a few milliseconds to start. The

start timing mainly depends on the crystal parameters.

Note: If bit 0 is cleared, and with the clock

output enabled, the oscillator continues to

run even if the OSCEN bit is cleared. The

device will not fully enter Sleep mode.

Note: Leaving blocks unnecessarily turned on

increases the current consumption, and

thus, decreases the battery life.

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