HMC832LP6GETR datasheet(16/49 Pages) AD

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Data Sheet

HMC832

Rev. A | Page 15 of 48

HMC832 SPI. As a result, writes to the PLL Register Map are

written directly and immediately, whereas the writes to the

VCO Subsystem Register Map are written to the PLL subsystem

to the VCO subsystem. This is a form of indirect addressing.

Note that VCO subsystem registers are write only and cannot be

read. More information is available in the VCO Serial Port

Interface (VSPI) section.

VCO Serial Port Interface (VSPI)

The HMC832 communicates with the internal VCO subsystem

via an internal 16-bit VCO SPI. The internal serial port controls

the step tuned VCO and other VCO subsystem functions.

Note that the internal VCO subsystem SPI (VSPI) runs at

the rate of the autocalibration FSM clock, tFSM, (see the VCO

Autocalibration section) where the FSM clock frequency

cannot be greater than 50 MHz. The VSPI clock rate is set

by Register 0x0A[14:13].

Writes to the control registers of the VCO are handled indirectly

via writes to Register 0x05 of the HMC832. A write to HMC832

packet, MSB first, across its internal serial link to the VCO

subsystem, where it is interpreted.

VSPI Use of Register 0x05

The packet data written into Register 0x05 is subparsed by logic

at the VCO subsystem into the following three fields:

Field 1—Bits[2:0]: 3-bit VCO_ID, target subsystem address =

000b.

Field 2—Bits[6:3]: 4-bit VCO_REGADDR, the internal register

address inside the VCO subsystem.

Field 3—Bits[15:7]: 9-bit VCO_DATA, data field to write to the

VCO register.

For example, to write 0_1111_1110 into Register 2 of the VCO

subsystem (VCO_ID = 000b), and set the VCO output divider

to divide by 62, the following needs to be written to

During autocalibration, the autocalibration controller writes

into the VCO register address specified by the VCO_ID

and VCO_REGADDR, as stored in Register 0x05[2:0] and

these values be zero (Register 0x05[6:0] = 0); otherwise, when

they are not zero (Register 0x05[6:0] ≠ 0), autocalibration does

not function.

To ensure that the autocalibration functions, it is critical to

write Register 0x05[6:0] = 0 after the last VCO subsystem write

prior to an output frequency change triggered by a write to

either Register 0x03 or Register 0x04.

However, it is impossible to write only Register 0x05[6:0] = 0

(VCO_REGADDR) without writing Register 0x05[15:7]

(VCO_DATA). Therefore, to ensure that the VCO_DATA

(Register 0x05[15:7]) in VCO_REGADDR 0x00 is not changed,

it is required to read the switch settings provided in Regis-

ter 0x10[7:0], and then rewrite them to Register 0x05[15:7], as

shown in the following example:

Read Register 0x10

Write to Register 0x05 the following:

Changing the VCO subsystem configuration (VCO Subsystem

in a failure to lock to the desired frequency.

For applications not using the read functionality of the

HMC832 SPI, in which Register 0x10 cannot be read, it is

possible to write Register 0x05 = 0x0 to set Register 0x05[6:0] =

0, which also sets the VCO subband setting equal to zero

(Register 0x05[15:7] = 0), effectively programming incorrect

VCO subband settings and causing the HMC832 to lose lock.

This procedure is then immediately followed by a write to:



This write effectively retriggers the autocalibration state

machine, forcing the HMC832 to relock whether in integer or

fractional mode.

This procedure causes the HMC832 to lose lock and relock after

every VCO subsystem change. Typical output frequency and

lock time is shown in Figure 27 and Figure 30, and is typically

in the order of 100 μs for a phase settling of 10°, and is also

dependent on loop filter design (loop filter bandwidth and loop

filter phase margin).

HMC832LP6GETR Datasheet(PDF) 16 Page - Analog Devices

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