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SPIRIT1 Datasheet, PDF (41/94 Pages) STMicroelectronics – Low data rate, low power sub-1GHZ transceiver
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SPIRIT1
Block description
signal within its dynamic range. After the down-conversion at IF, a first order filter is
implemented to attenuate the out-of-band blockers.
8.9
Transmitter
The SPIRIT1 contains an integrated PA capable of transmitting at output levels between -30
dBm to +11 dBm. The PA is single-ended and has a dedicated pin (TXOUT). The PA output
is ramped up and down to prevent unwanted spectral splatter. In TX mode the PA drives the
signal generated by the frequency synthesizer out to the antenna terminal. The output
power of the PA is programmable via SPI. Delivered power, as well as harmonic content,
depends on the external impedance seen by the PA. To obtain approval on ETSI EN 300
220, it is possible to program TX to send an unmodulated carrier.
The output stage is supplied from the SMPS through an external choke and is loaded with a
LC-type network which has the function of transforming the impedance of the antenna and
filter out the harmonics. The TX and RX pins are tied directly to share the antenna. During
TX, the LNA inputs are internally shorted to ground to allow for the external network
resonance, so minimizing the power loss due to the RX.
Figure 7. Shaping of ASK signal
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8.10
Temperature sensors (TS)
The SPIRIT1 can provide an analog temperature indication as a voltage level, which is
available at the GPIO_0 pin. The voltage level V0 at room temperature (or any other useful
reference temperature) should be acquired and stored by the MCU in order to compensate
for the offset. The relationship between temperature and voltage is the following:
Equation 1
T = 400 ⋅ (Vtemp – V0) + (T0 + 3.75)
(° C)
where V0 is the voltage at temperature T0.
Doc ID 022758 Rev 3
41/94
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