HMC833LP6GE datasheet(32/61 Pages) HITTITE

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HMC833LP6GE

v01.1012

FRACTIONAL-N PLL WITH INTEGRATED VCO

25 - 6000 MHz

with a phase offset. A phase offset is implemented by adding a constant DC offset current at the output of

the charge pump.

DC offset may be added to the UP or DN switching pumps using Reg 09h[21] or Reg 09h[22]. The

magnitude of the offset is controlled by Reg 09h[20:14], and can range from 0 to 635 µA in steps of 5 µA.

Down offset is highly recommended in fractional mode of operation. Integer mode of operation works best

with zero offset.

As an example, a PD comparison of fPD = 50 MHz (20 ns period) with the main pump gain set at 2 mA, and

a down (DN) offset of -385 µA would represent a phase offset of about (-385/2000)*360 = -69 degrees.

This is equivalent to the divided VCO arriving 3.8 ns after the reference at the PD input. It is critical that

phase offset be used in fractional mode. Normally, down offsets larger than 3 ns are typical.

If the charge pump gain is changed, for example to compensate for changes in VCO sensitivity, it is

recommended to change the charge pump offset proportionally to maintain a constant phase offset.

Figure 47. Charge Pump Gain & Offset Control

1.12

Frequency Tuning

HMC833LP6GE VCO subsystem always operates in fundamental frequency of operation (1500 MHz to

3000 MHz). The HMC833LP6GE generates frequencies below its fundamental frequency (25 MHz to

1500 MHz) by tuning to the appropriate fundamental frequency and selecting the appropriate Output

Divider setting (divide by 2/4/6.../60/62) in VCO_Reg 02h[5:0]. Conversely the HMC833LP6GE generates

frequencies greater than its fundamental frequency (3000 MHz to 6000 MHz) by tuning to the appropriate

fundamental frequency and enabling the doubler mode (VCO_Reg 03h [0] = 1).

The HMC833LP6GE automatically controls frequency tuning in the fundamental band of operation, for

more information see “1.2.1 VCO Auto-Calibration (AutoCal)”.

To tune to frequencies below the fundamental frequency range (<1500 MHz) it is required to tune the

HMC833LP6GE to the appropriate fundamental frequency, then select the appropriate output divider setting

(divide by 2/4/6.../60/62) in VCO_Reg 02h[5:0]. Similarly, to tune to frequencies above the fundamental

frequency range (> 3000 MHz) it is required to tune the HMC833LP6GE to the appropriate fundamental

frequency, and then enable the doubler mode of operation (VCO_Reg 03h [0] = 1).

1.12.1 Integer Mode

The HMC833LP6GE is capable of operating in integer mode. For Integer mode set the following registers

a. Disable the Fractional Modulator, Reg 06h[11]=0

b. Bypass the Modulator circuit, Reg 06h[7]=1

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