STW81103 datasheet(23/53 Pages) STMICROELECTRONICS

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STW81103

Circuit description

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5.8

Voltage controlled oscillators

5.8.1

VCO selection

The STW81103 integrates two low-noise VCOs to cover a wide band from:

●

2500 MHz to 3050 MHz and from 4350 MHz to 5000 MHz (direct output)

●

1250 MHz to 1525 MHz and from 2175 MHz to 2500 MHz (selecting divider by 2)

●

625 MHz to 762.5 MHz and from 1087.5 MHz to 1250 MHz (selecting divider by 4)

The frequency range is 2500 MHz-3050 MHz for VCO A, and 4350 MHz-5000 MHz for VCO

5.8.2

VCO frequency calibration

Both VCOs can operate on 32 frequency ranges that are selected by adding or subtracting

capacitors from the resonator. These frequency ranges are intended to cover the wide band

of operation and compensate for process variation on the VCO center frequency.

The range is automatically selected when the SERCAL bit is set to 1. The charge pump is

inhibited, and the ICP and VCTRL pins are at VDD/2 volts. The ranges are then tested with

this VCO input voltage to select the one nearest to the desired output frequency

(FOUT = N*Fref/R).

After this selection, the SERCAL bit is automatically reset to 0 and the charge pump is once

again enabled. To enable a fast settle, the PLL needs only to perform fine adjustments

around VDD/2 on the loop filter to reach FOUT.

Figure 19.

VCO sub-bands frequency characteristics

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