Si4421
Description of the Control Commands |
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1. | Configuration Setting Command |
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| Bit |
| 15 | 14 | 13 | 12 | 11 | 10 |
| 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | POR |
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| 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 | Frequency Band |
0 | 0 | Reserved |
0 | 1 | 433 |
1 | 0 | 868 |
1 | 1 | 915 |
2. Power Management Command
x3
0
0
0
0
1
1
x2 |
| x1 | x0 | Crystal Load Capacitance [pF] |
0 |
| 0 | 0 | 8.5 |
0 |
| 0 | 1 | 9.0 |
0 |
| 1 | 0 | 9.5 |
0 |
| 1 | 1 | 10.0 |
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| … |
1 |
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| 1 | 0 | 15.5 | |
1 |
| 1 | 1 | 16.0 |
| Bit |
| 15 |
| 14 | 13 | 12 | 11 |
| 10 | 9 | 8 | 7 |
| 6 | 5 |
| 4 | 3 |
| 2 | 1 | 0 | POR |
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| 1 |
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| 0 | 0 | 0 | 0 |
| 0 | 1 | 0 | er |
| ebb | et |
| es | ex |
| eb | ew | dc | 8208h |
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| Bit |
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| Function of the control bit |
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| Related blocks |
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| er |
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| Enables the whole receiver chain |
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| RF front end, baseband, synthesizer, crystal oscillator |
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| ebb |
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| The receiver baseband circuit can be separately switched on |
| Baseband |
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| et |
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| Switches on the PLL, the power amplifier, and starts the |
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| Power amplifier, synthesizer, crystal oscillator |
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| transmission (If TX register is enabled) |
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| es |
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| Turns on the synthesizer |
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| Synthesizer |
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| ex |
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| Turns on the crystal oscillator |
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| Crystal oscillator |
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| eb |
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| Enables the low battery detector |
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| Low battery detector |
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| ew |
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| Enables the |
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| dc |
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| Disables the clock output (pin 8) |
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| Clock output buffer |
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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.
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