HMC1197LP7FE datasheet(17/57 Pages) AD

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HMC1197LP7FE

v03.0314

Wideband direct Quadrature Modulator

w/ Fractional-n Pll & Vco, 100 - 4000 MHz

1.2

Vco overview

The VCO consists of a capacitor switched step tuned VCO and an output stage. In typical operation, the

VCO is programmed with the appropriate capacitor switch setting which is executed automatically by the

PLL AutoCal state machine if AutoCal is enabled (Reg 0Ah[11] = 0, see section “1.2.1 VCO Calibration” for

more information). The VCO tunes to the fundamental frequency (2050 MHz to 4100 MHz), and is locked

by the CP output from the PLL subsystem. The VCO controls the output stage of the HMC1197LP7FE

enabling configuration of:

•

VCO Output divider settings configured in Reg 16h (divide by 2/4/6...60/62 to generate frequencies

from 33 MHz to 2050 MHz, or divide by 1 to generate fundamental frequencies between 2050 MHz

and 4100 MHz)

•

Output gain settings (Reg 16h[7:6], Reg 16h[9:8])

•

Single-ended or differential output operation (Reg 17h[9:8])

•

Always Mute (Reg 16h[5:0])

•

Mute when unlock (Reg 17h[7])

1.2.1

Vco calibration

1.2.1.1 Vco auto-calibration (autocal)

The HMC1197LP7FE uses a step tuned type VCO. A step tuned VCO is a VCO with a digitally selectable

capacitor bank allowing the nominal center frequency of the VCO to be adjusted or ‘stepped’ by switching

in/out VCO tank capacitors. A step tuned VCO allows the user to center the VCO on the required output

frequency while keeping the varactor tuning voltage optimized near the mid-voltage tuning point of the

HMC1197LP7FE’s charge pump. This enables the PLL charge pump to tune the VCO over the full range of

operation with both a low tuning voltage and a low tuning sensitivity (kvco).

The VCO switches are normally controlled automatically by the HMC1197LP7FE using the Auto-Calibration

feature. The Auto-Calibration feature is implemented in the internal state machine. It manages the selection

of the VCO sub-band (capacitor selection) when a new frequency is programmed. The VCO switches may

also be controlled directly via register Reg 15h for testing or for other special purpose operation.

To use a step tuned VCO in a closed loop, the VCO must be calibrated such that the HMC1197LP7FE

knows which switch position on the VCO is optimum for the desired output frequency. The HMC1197LP7FE

supports Auto-Calibration (AutoCal) of the step tuned VCO. The AutoCal fixes the VCO tuning voltage at

the optimum mid-point of the charge pump output, then measures the free running VCO frequency while

searching for the setting which results in the free running output frequency that is closest to the desired

phase locked frequency. This procedure results in a phase locked oscillator that locks over a narrow

voltage range on the varactor. A typical tuning curve for a step tuned VCO is shown in Figure 36.Note how

the tuning voltage stays in a narrow range over a wide range of output frequencies such as fast frequency

hopping.

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rights of third parties that may result from its use. Specifications subject to change without notice. No

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