RTX-24EM
User guide
The technical characteristics can change without notice. AUR°EL S.p.A doesn’t assume the responsibility to the damages caused by an improper use of the device.
AUR°EL S.p.A.
Via Foro dei Tigli, 4 - 47015 Modigliana (FC) – ITALY 12/11/2019 - Rev. B
Tel.: +390546941124 – Fax: +390546941660 Page 20
http://www.aurel.it
The calibration of the PTAT is independent of the temperature and only needs to be executed once when
the chip is powered. Because this value should be constant during product life, it is possible to do
calibration only once and to store
RAM2@5<3:0>
value somewhere in a non-volatile memory.
Write_RAM2
SPI command with this pre-stored value could then be used to set the correct internal PTAT
current.
9.4
VCO auto calibration
This auto-calibration is used to calibrate the analog circuits of the PLL. For correct transmission and
reception, the PLL should be calibrated at each channel frequency to be used before the link is established
or if the operating temperature changes by more than 10 to 20 °C.
The EM9209 has a dedicated subroutine located at the
ROM_Boot_Address
=
64
which will perform the
VCO auto calibration.
Auto calibration frequency is set through register
VcoCalibFreq[11:0]
which is located in
RAM1
at the
address
53
. It must be programmed through the SPI
Write_RAM1
command to fit the required frequency
operation.
VcoCalibFreq[11:0]
is:
VcoCalibFreq[7:0]
= (round(4259840 / fo) – 1618).
VcoCalibFreq[11:8]
= 0b1011 (0xB).
where fo is the RF operating frequency in MHz.
Examples:
fo = 2480, VcoCalibFreq[11:0] = 0xB64.
fo = 2440, VcoCalibFreq[11:0] = 0xB80.
fo = 2400, VcoCalibFreq[11:0] = 0xB9D.
To perform the auto calibration:
•
ENABLE (Pin 10) or nRESET (Pin 4) must be set to Vcc.
•
Crystal oscillator must be started (see section 9.2)
•
RB_Inst_Dis must be set to 1 (if RB_Inst_Dis has been previously set = 1, see section 9.2, this step can
be omitted).
•
Use SPI command
ROM_Boot
with argument
ROM_Boot_Address
=
64.
•
Use SPI command
Write_RAM1
with address =
53
and data_write =
VcoCalibFreq[11:0].
•
Use then the SPI command
Start_Micro
.
•
The end of auto calibration will be signaled with IRQ going high. SPI command
Clear_IRQ
allows
clearing the interrupt.
The calibration of the PLL may vary if the external conditions change (e.g., temperature), therefore
calibration should be repeated periodically.
