AK1572 Datasheet, PDF (27/35 Pages) Asahi Kasei Microsystems – Down Converter Mixer with Fractional-N Frequency Synthesizer and VCO

[AK1572]
15. VCO
Calibration
AK1572 has three VCO core in uses several overlapping bands to allow low Phase Noise, low VCO
sensitivity (K_VCO) and wide frequency range. The selection which VCO should be used can be done
by the register {VCO[1:0]} in <Address 0x01>. Moreover, the correct band is chosen automatically at
frequency setting, which is called calibration.
The calibration starts when <Address0x01> are written in the condition that {MODE[1]} in <Address
0x04>=”0” and [PDN] pin=“H”. During the calibration, V_TUNE of VCO is disconnected from the
output of the loop filter and connected to an internal reference voltage. The charge pump output is
disabled.
The internal bias must be stable so that the calibration is done correctly. Therefore, it is necessary to
wait 500sec at least until <Address0x01> writing after [PDN] rises up.
The register {CALTM [3:0]} determines the calibration time. When {CALTM [3:0]} is larger, the
calibration precision increases, but the required time becomes long as a trade-off. The value
calculated by the following formula is recommended to get enough calibration precision. However,
{CALTM [3:0]} should be set at from 1 to 11. 0 and over 11 is prohibited.
{CALTM[3:0]} ≥ log₂(F_PFD / 20000)
F_PFD : PFD frequency
The calibration time can be estimated as following calculation;
Calibration time = 1 /F_PFD × {(6 + 2^ {CALTM [3:0]}) ×8 + 3}
MS1551-E-00
27
2013/8