ADMV4530 datasheet(34/64 Pages) AD

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Data Sheet

ADMV4530

THEORY OF OPERATION

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Rev. C | 34 of 64

MUXOUT

The output multiplexer on the ADMV4530 allows the user to access

various internal signals on the chip. The MUXOUT bit field (Register

0x020, Bits[7:4]) shown in Table 34 lists the available signals. When

MUXOUT_SEL (Register 0x20, Bit 3) is set to 1, the MUXOUT

signal is present on the SDO output pin. Otherwise, the SDO pin is

configured for SPI data output.

DIGITAL LOCK DETECT

A digital lock detect function is available on the SDO pin when both

the MUXOUT and MUXOUT_SEL bits are set to 1. The digital lock

detect function is also available by reading the LD_READBACK bit

(Register 0x07C, Bit 0). A logic high indicates that the digital lock

detect has declared the PLL is locked.

The digital lock detect function has some adjustable settings in

adjust an internal precision window and the LD_COUNT bits adjust

the consecutive cycle count to declare PLL lock. It is recommended

to keep the settings listed in the register map. For special applica-

tions, contact Analog Devices Technical Support for guidance on

adjusting these settings.

VCO AUTOCALIBRATION

The internal VCO uses an internal autocalibration routine that opti-

mizes the VCO settings for a particular frequency and allows the

PLL to lock in approximately 100 µs after the lower portion of

the N counter integer value (Register 0x010) is programmed. For

nominal applications, maintain the autocalibration default values in

the register map (Register 0x030 to Register 0x034).

For applications where it is desirable to bypass the autocalibration

routine, there are two necessary procedures. First, generate a

lookup table of the resultant VCO calibration data (core and band

parameters) for each desired VCO frequency. Second, bypass the

autocalibration routine and manually write the lookup table values.

Generate a new table for every chip because each chip is unique.

VCO CALIBRATION DATA READ BACK

To read back the VCO calibration data, load the required registers,

let the device lock using autocalibration, and read the VCO parame-

ters for each frequency. It is important to ensure that autocalibration

has completed before readback. Reading back values before auto-

calibration has completed results in incorrect values being read.

The bits used for read back include the following:

►

The VCO_FSM_READBACK bits set what data is sent to the

VCO_DATA_READBACK bits.

To read the VCO parameters, take the following steps:

1. Program the device to lock at the desired frequency by using

the autocalibration feature. Users must wait for the device to

lock.

2. Set VCO_FSM_READBACK = 1 to allow readback of the VCO

band and the core.

3. Read Register 0x06F, Bit 0 to read back the current VCO core.

The ADMV4530 has only one VCO core. Therefore, this value

must always be 1.

4. Read Register 0x06E, Bits[4:0] to read back the VCO band.

Repeat Step 1 through Step 4 for each required frequency to build

a lookup table of values.

VCO CALIBRATION DATA MANUAL WRITING

The VCO parameters for each required frequency force the device

to the target frequency core and band without the use of autocali-

bration.

The bits used for writing to the VCO parameters include the follow-

ing:

►

To write the VCO parameters, take the following steps:

1. At power-up, set up the serial port interface and initialize the

device as necessary for normal operation.

2. Set AUTOCAL_EN = 0 (Register 0x012, Bit 6) to disable auto-

calibration.

3. Set VCO_FSM_TEST_MODES = 010 to overwrite the VCO

core and band.

4. Program the registers, except Register 0x010, as required for

the target frequency. This step is frequency dependent.

5. Set SI_VCO_SEL = 1. Even though the ADMV4530 has only

one VCO core, it is still necessary to program this bit because

this bit tells the internal finite state machine to enable the VCO.

6. Set SI_BAND_SEL to the desired band from the previously

generated lookup table.

7. Write to Register 0x010. When this register is written to, the de-

vice locks to the new frequency.

Repeat Step 4 through Step 7 as required for setting the appropri-

ate VCO frequency.

AUTOCALIBRATION LOCK TIME

The PLL lock time divides into a number of settings. The total lock

time for changing frequencies is the sum of three separate times:

synthesizer lock, VCO band selection, and PLL settling.

ADMV4530 Datasheet(PDF) 34 Page - Analog Devices

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