HMC832LP6GETR datasheet(20/49 Pages) AD

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Data Sheet

HMC832

Control Value Register 0x0A[2:0]

tMMT (µs)

tCAL (µs)

fERR Maximum

1.28

12.48

±390 kHz

128

2.56

20.16

± 95 kHz

256

5.12

35.52

±98 kHz

VCO Autocalibration Example

The VCO subsystem must satisfy the maximum fPD limited by

the two following conditions:

N ≥ 16 (fINT), N ≥ 20.0 (fFRAC)

where N = fVCO/ fPD.

fPD ≤ 100 MHz

For example, if the VCO subsystem output frequency is to

operate at 2.01 GHz and the crystal frequency is fXTAL = 50 MHz,

R = 1, and m = 0 (see Figure 42), then tFSM = 20 ns (50 MHz).

Note that when using autocalibration, the maximum autocali-

bration finite state machine (FSM) clock cannot exceed 50 MHz

(see Register 0x0A[14:13]). The FSM clock does not affect the

accuracy of the measurement, it only affects the time to produce

the result. This same clock is used to clock the 16-bit VCO

serial port.

If time to change frequencies is not a concern, then the

calibration time for maximum accuracy can be set, and

therefore, the measurement resolution is of no concern.

Using an input crystal of 50 MHz (R = 1 and fPD = 50 MHz) the

times and accuracies for calibration using Equation 6 and

Equation 8 are listed in Table 7, where minimal tuning time is

1/8th of the VCO band spacing.

Across all VCOs, a measurement resolution better than 800 kHz

produces correct results. Setting m = 0 and n = 5, provides

781 kHz of resolution and adds 8.6 μs of autocalibration time to

a normal frequency hop. After the autocalibration sets the final

switch value, 8.64 μs after the frequency change command, the

fractional register is loaded, and the loop locks with a normal

transient predicted by the loop dynamics. Therefore, as shown

in this example, autocalibration typically adds about 8.6 μs to

the normal time to achieve frequency lock. Use autocalibration

for all but the most extreme frequency hopping requirements.

Manual VCO Calibration for Fast Frequency Hopping

When switching frequencies quickly is needed, it is possible to

eliminate the autocalibration time by calibrating the VCO in

advance and storing the switch number vs. frequency infor-

mation in the host. This is accomplished by initially locking the

HMC832 on each desired frequency using autocalibration, then

reading and storing the selected VCO switch settings. The VCO

switch settings are available in Register 0x10[7:0] after every

autocalibration operation. The host must then program the

VCO switch settings directly when changing frequencies.

Manual writes to the VCO switches are executed immediately as

are writes to the integer and fractional registers when

autocalibration is disabled. Therefore, frequency changes with

manual control and autocalibration disabled requires a

minimum of two serial port transfers to the PLL, once to set the

VCO switches and once to set the PLL frequency.

When autocalibration is disabled, Register 0x0A[11] = 1, the

VCO updates its registers immediately with the value written

via Register 0x05. The VCO internal transfer requires 16 VSCK

clock cycles after the completion of a write to Register 0x05.

VSCK and the autocalibration controller clock are equal to the

input reference divided by 0, 4, 16, or 32 as controlled by

Registers Required for Frequency Changes in Fractional

Mode

In fractional mode (Register 0x06[11] = 1), a large change of

frequency may require main serial port writes to one of the

three following registers

•

The integer register, INTG, Register 0x03. This is required

only if the integer part changes.

•

The VCO SPI register, Register 0x05. This is required only

for manual control of VCO if Register 0x0A[11] = 1,

autocalibration is disabled, or to change the VCO output

divider value (VCO_REG 0x02), see Figure 39 for more

information.

•

The fractional register, Register 0x04. The fractional register

write triggers autocalibration when Register 0x0A[11] = 0,

and it is loaded into the modulator automatically after the

autocalibration runs. If autocalibration is disabled, Regis-

ter 0x0A[11] = 1, the fractional frequency change is loaded

immediately into the modulator when the register is

written with no adjustment to the VCO.

Small steps in frequency in fractional mode, with autocalibration

enabled (Register 0x0A[11] = 0), usually require only a single

write to the fractional register. In a worst-case scenario, three

main serial port transfers to the HMC832 could be required to

change frequencies in fractional mode. If the frequency step is

small and the integer part of the frequency does not change,

then the integer register is not changed. In all cases, in frac-

tional mode, it is necessary to write to the fractional register,

Rev. A | Page 19 of 48

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