STW81101AT datasheet(22/48 Pages) STMICROELECTRONICS

22 / 48 page

Circuit description

STW81101

22/48

5.8

Voltage controlled oscillators

5.8.1

VCO selection

The STW81101 integrates two low-noise VCOs to cover a wide band from:

●

3300MHz to 4400MHz (direct output)

●

1650MHz to 2200MHz (selecting divider by 2)

●

825MHz to 1100MHz (selecting divider by 4)

VCO A frequency range is 3300 MHz to 3900MHz.

VCO B frequency range 3800 MHz to 4400MHz.

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 rises from 0 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 signal ENDCALB (which means End of Calibration) falls to 0, and the

charge pump is once again enabled. Additionally, the SERCAL bit should be reset to 0 before

the next channel step. To enable a fast settle, the PLL needs only to perform fine adjustment

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

Figure 19.

VCO sub-bands frequency characteristics

STW81101AT Datasheet(PDF) 22 Page - STMicroelectronics