FXTH870xD
Sensors
132
Freescale Semiconductor, Inc.
13.21
VCO Calibration Machine
The RFM incorporates a VCO calibration machine which works in conjunction with the VCO. The calibration machine selects the
optimal VCO sub-band with respect to a predefined reference voltage applied to the VCO.
•
Calibration supports maxband VCO sub-bands. maxband corresponds to the band where the VCO frequency is maximum.
•
A successive approximation algorithm is used to calculate the optimum sub-band.
•
F
c
, the Center Frequency (AFREQ+BFREQ)/2 is used as the reference frequency for the VCO calibration in FSK mode
(MOD = 1).
•
BFREQ is used as the reference frequency for the VCO calibration in OOK mode (MOD = 0).
•
Calibration occurs every time the VCO is enabled.
•
The calibration takes approximately 5
s.
The state machine of the calibration is shown in
Figure 112
.
Figure 112. VCO Calibration State Machine
Count the number of cycles of the VCO
Compare
VCOcount<Targetedcount
VCOband=maxband/2
VCOcount and Targetedcount
Bestband=maxband/2
VCOband=VCOband-Difference
Difference=maxband/4
Difference=Difference/2
VCOband=Difference
VCOband=VCOband-Difference
Bestband=VCOband
Difference=1?
NO
YES
Bestband is first best band found
or the closest band found
- maxband is the number
of sub-band of the VCO
- Bestband is the band which
is going to be chosen
- Difference is an internal variable.
VCOcount=Targetedcount
VCOcount>Targetedcount
Summary of Contents for FXTH870 D Series
Page 86: ...FXTH870xD Sensors 84 Freescale Semiconductor Inc Figure 57 Data Flow For Measurements...
Page 171: ...FXTH870xD Sensors Freescale Semiconductor Inc 169 Figure 128 QFN Case Outline...
Page 172: ...FXTH870xD Sensors 170 Freescale Semiconductor Inc Figure 129 QFN Case Outline...
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