Silicon Laboratories SI4421 - Manual (Page 15)

Si4421
15
Description of the Control Commands
1. Configuration Setting Command
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 POR
1 0 0 0 0 0 0 0 el ef b1 b0 x3 x2 x1 x0 8008h
Bit el enables the internal data register.
Bit ef enables the FIFO mode. If ef = 0 then DATA (pin 6) and DCLK (pin 7) are used for data and data clock output.
b1 b0 Freq y Ba uenc nd
0 0 Reserved
0 1 3 43
1 0 8 86
1 1 5 91
x3 x2 x1 x0 Crystal Load Capacitance [pF]
0 8.5 0 0 0
0 9.0 0 0 1
0 9.5 0 1 0
0 10.0 0 1 1
…
1 15.5 1 1 0
1 16.0 1 1 1
2. Power Management Command
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 POR
1 0 0 0 0 0 1 0 er ebb et es ex eb ew dc 8208h
Bit Function of the control bit Related blocks
er Enables the whole receiver chain RF front end, baseband, synthesizer, crystal oscillator
ebb The receiver baseband circuit can be separately switched on Baseband
et
Switches on the PLL, the power amplifier, and starts the
transmission (If TX register is enabled)
Power amplifier, synthesizer, crystal oscillator
es Turns on the synthesizer Synthesizer
ex Turns on the crystal oscillator Crystal oscillator
eb Enables the low battery detector Low battery detector
ew Enables the wake-up timer Wake-up timer
dc Disables the clock output (pin 8) Clock output buffer
The ebb, es, and ex bits are provided to optimize the TX to RX or RX to TX turnaround time.
The RF frontend consist of the LNA (low noise amplifier) and the mixer. The synthesizer block has two main components: the VCO
and the PLL. The baseband section contains the baseband amplifier, low pass filter, limiter and the I/Q demodulator.
To decrease TX/RX turnaround time, it is possible to leave the baseband section powered on. Switching to RX mode means disabling
the PA and enabling the RF frontend. Since the baseband block is already on, the internal startup calibration will not be performed,
the turnaround time will be shorter.
The synthesizer also has an internal startup calibration procedure. If quick RX/TX switching needed it may worth to leave this block
on. Enabling the transmitter using the et bit will turn on the PA, the synthesizer is already up and running. The power amplifier almost
immediately produces TX signal at the output.
The crystal oscillator provides reference signal to the RF synthesizer, the baseband circuits and the digital signal processor part.
When the receiver or the transmitter part frequently used, it is advised to leave the oscillator running because the crystal might need
a few milliseconds to start. This time mainly depends on the crystal parameters.
It is important to note that leaving blocks unnecessary turned on can increase the current consumption thus decreasing the battery
life.