AK1573 Datasheet, PDF (33/42 Pages) Asahi Kasei Microsystems – Low Noise Integrated VCO

[AK1573/AK1573B/AK1573C]
13.4. VCO
Calibration
The VCO core in AK1573 uses several overlapping bands to achieve low Phase Noise, low
VCO sensitivity (K_VCO) and wide frequency range. The correct band is chosen automatically at
frequency setting by VCO calibration. The calibration starts when A counter and B counter in
<Address0x01> are set. During the calibration, VCO V_CNT is disconnected from the external
loop filter and connected to an internal reference voltage. The charge pump output is Tri-State.
The internal reference voltage must be stable so that the calibration is done correctly.
Therefore, it is necessary to wait 10sec at least until <Address0x01> is set after PDN2 pin
rises up to “1” (when 100pF is connected to SCAP pin).
The register CALTM[3:0] bits set the calibration precision and time. The larger CALTM[3:0] bits
are set, the higher calibration precision becomes, but the longer calibration time is required as
trade-off. Set the value calculated by the following formula to get enough calibration precision.
However, CALTM[3:0] bits should be set from 0 to 10. Over 11 are prohibited.
CALTM[3:0] bits ≥ 10 - log( B[12:0] ) / log(2)
The calibration time can be estimated as following formula;
Calibration time = 1 /F_PFD × 11 × 2 ^ CALTM[3:0] bits
It is prohibited to set frequency once again until VCO calibration and Fast lock-up mode is
completed.
Low Current Mode
The AK1573 goes into low current mode by setting VCOI bit in <Address0x04> to “0”. This
mode decreases VCO core current but Phase Noise gets worse compared to normal mode.
015009351-E-00
- 33 -
2015/8