
AD9530 Data Sheet
Rev. 0 | Page 20 of 41
RTWO Calibration
The RTWO calibration function selects the appropriate RTWO
frequency band for a given configuration. A calibration is
performed by toggling Register 0x001, Bit 2 from 0 to 1. The
command sequence to issue a VCO calibration is as follows:
1. Write the desired AD9530 configuration, including the
divider and output driver settings.
2. Set Register 0x001, Bit 2 = 0 (CALIBRATE VCO bit).
Note that this is a self clearing bit.
A calibration is required after initial power-up, after subsequent
resets, and after any changes to the input reference frequency or
the divide settings that affect the RTWO operating frequency. A
2 sec wait timer is activated at power-up to gate the first calibration.
This wait time is not enforced for subsequent calibrations after
power-on. See the CML Output Drivers section for more
details. The PLL reference must be active and stable and the
PLL must be configured to a valid operational state prior to
issuing a calibration. After a calibration, all of the internal
dividers are synchronized automatically to ensure proper phase
alignment of the PLL and distribution.
Reference Switchover
The AD9530 supports two separate differential reference inputs.
Manual switchover is performed between these inputs by either
writing to Register 0x011, Bit 2 and Bit 1, or by using the REF_SEL
pin. Register 0x011, Bit 2 sets whether the REF_SEL pin or the
reference select register controls the reference input mux. Default
operation ignores the REF_SEL pin setting and uses the value of
Register 0x011, Bit 1.
Dividers (R, Mx, N, and Dx)
The AD9530 contains multiple dividers that configure the PLL
for a given frequency plan. Each divider has an associated reset
bit that is self clearing. Resetting a divider is required every time
the divide value of that driver is changed. Issuing a reset of a
single divider does not clear the current divide value.
Reference Divider (R Divider)
The reference inputs are routed through a 2:1 mux into a
common 8-bit R divider. R can be set to any value from 1 to 255
(Register 0x010, Bits[7:0]). Setting Register 0x010 = 0x0A is
equivalent to an R divider setting of 10.
The frequency out of the R divider must not exceed the maximum
allowable frequency of the PFD listed in Table 5.
The R divider has its own reset located in Register 0x011. This
reset bit is self clearing.
M3 and N Feedback Dividers
The total feedback division from the RTWO to the PFD is the
product of the M3 and N dividers. The N divider (Register 0x023,
Bits[7:0]) functions identically to the R divider described in the
Reference Divider (R Divider) section. The M3 divider
(Register 0x022, Bits[3:2]) is limited to fixed divide values of 2,
2.5, 3, and 3.5 and acts as a prescaler to the N divider. The M3
and N dividers have individual resets located at Register 0x022,
Bit 0, and Register 0x024, Bit 0, respectively.
M1 and M2 Dividers (M1 and M2)
The M1 and M2 dividers (Register 0x020, Bits[4:3] and
Register 0x021, Bits[4:3], respectively) have fixed divide
values of 2, 2.5, 3, and 3.5.
The M1 and M2 dividers provide frequency division between the
RTWO output and the clock distribution channel dividers (Dx).
The M1 and M2 dividers have individual resets located at
Register 0x020, Bit 0, and Register 0x021, Bit 0, respectively.
Channel Dividers (Dx)
The AD9530 has four 8-bit channel dividers (Dx) which are
identical to the R and N dividers. Dx can be set to any value
from 1 to 255. Setting the divide value for D1 through D4 is
accomplished by writing Register 0x014, Register 0x016,
Register 0x018, and Register 0x01A, respectively. The D1 through
D4 reset bits that reset D1 through D4 are located in Bit 0 of
Register 0x015, Register 0x017, Register 0x019, and
Register 0x01B, respectively. A setting of 0 disables the divider.
Dividers Sync
Use a sync to phase align all of the AD9530 internal dividers to a
common point in time. A global sync of all dividers is performed
after a VCO calibration. To perform a VCO calibration, write a
1 to Bit 2 of Register 0x001. A VCO calibration must be
performed after power up, as well as any time a different VCO
frequency is selected.
To sync all of the dividers after programming them, without the
VCO frequency, write a 1 to Bit 1 of Register 0x001.
Lock Detector
The AD9530 features a frequency lock detect signal that
corresponds to whether the PLL reference and feedback edges are
within a certain frequency of one another. The exact frequency
lock threshold to indicate a PLL lock is user programmable in
Register 0x01D, Bits[3:1]. The three register bits allow the
frequency lock threshold to span ±20 ppb to ±300 ppm.
If the frequency error between the reference and feedback edges
is lower than the specified lock threshold, the LD pin goes high and
the PLL_LOCKED bit = 1. The LD pin and the PLL_LOCKED bit
go low when the error between the reference and feedback
edges is greater than the frequency lock threshold.
The lock detector also outputs an 11-bit word located in
Register 0x01E, Bits[7:0] and Register 0x01F, Bits[1:0]. Bit 10
through Bit 0 contain a binary value representative of the measured
frequency lock error, and Bit 11 indicates whether the 10-bit
value is expressed in ppm (parts per million) or ppb (parts per
billion). Note that this 11th bit is found in Register 0x01F, Bit 3.