New-Tech Europe Magazine | Q3 2020

Figure 1: Block diagram of a phase-locked loop.

such as the ADF4150HV from Analog Devices, Inc. (ADI), which does not require an additional active loop filter, can be used. Although both solutions require a high voltage supply, the number of components can be reduced with the ADF4150HV. The distortion and phase noise caused by the active filter amplifier can also be avoided. Furthermore, the ADF4150HV permits implementation of fractional-N or integer-N phase-

locked loop frequency synthesizers. Thus, the VCO frequency can be divided by 1, 2, 4, 8, or 16 so that output frequencies down to a minimum of 31.25 MHz are possible. The high voltage required for the ADF4150HV’s integrated charge pump can be generated with the dc-to-dc boost converter ADP1613 without any compromises in PLL performance. The ADP1613 is an effective switching regulator with integrated power transistor for

easily achieving output voltages of up to 20 V. Higher output voltages are also possible by using additional external components, especially through an external power transistor. The switching frequency of the ADP1613 can be adjusted in a range from 650 kHz to 1.3 MHz. This leads to a better transient response and simple noise filtering. In general, selecting a switching frequency of greater than 1 MHz is recommended so that switching

Figure 2: Simplified circuit of a high voltage charge pump supply for the ADF4150HV.

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