HMC1197LP7FE datasheet(22/57 Pages) AD

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HMC1197LP7FE

v03.0314

Wideband direct Quadrature Modulator

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

1.3

Pll overview

1.3.1

charge Pump (cP) & Phase detector (Pd)

The Phase detector (PD) has two inputs, one from the reference path divider and one from the RF path

divider. When in lock these two inputs are at the same average frequency and are fixed at a constant

average phase offset with respect to each other. We refer to the frequency of operation of the PD as fpd.

Most formulae related to step size, delta-sigma modulation, timers etc., are functions of the operating

frequency of the PD, fpd. fpd is also referred to as the comparison frequency of the PD.

The PD compares the phase of the RF path signal with that of the reference path signal and controls the

charge pump output current as a linear function of the phase difference between the two signals. The

output current varies linearly over a full ±2π radians (±360°) of input phase difference.

1.3.1.1 charge Pump

A simplified diagram of the charge pump is shown in Figure 38. The CP consists of 4 programmable

current sources, two controlling the CP Gain (Up Gain Reg 09h[13:7], and Down Gain Reg 09h[6:0]) and

two controlling the CP Offset, where the magnitude of the offset is set by Reg 09h [20:14], and the direction

is selected by Reg 09h [21]=1 for up and Reg 09h [22]=1 for down offset.

CP Gain is used at all times, while CP Offset is only recommended for fractional mode of operation.

Typically the CP Up and Down gain settings are set to the same value (Reg 09h[13:7] = Reg 09h[6:0]).

Figure 38. Charge Pump Gain & Offset Control

1.3.1.2 charge Pump Gain

Charge pump Up and Down gains are set by Reg 09h[13:7] and Reg 09h[6:0] respectively. The current gain

of the pump in Amps/radian is equal to the gain setting of this register divided by 2π.

Typical CP gain setting is set to 2 to 2.5 mA, however lower values can also be used. Values < 1 mA may

result in degraded Phase Noise performance.

For example, if both Reg 09h[13:7] and Reg 09h[6:0] are set to ‘50d’ the output current of each pump will

be 1 mA and the phase frequency detector gain kp = 1 mA/2π radians, or 159 µA/rad.

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