STW81102 datasheet(20/43 Pages) STMICROELECTRONICS

20 / 43 page

General description

STW81102

20/43

Figure 18.

Loop filter connection

4.1.8

Voltage controlled oscillators

VCO Selection

Within STW81102 two low-noise VCOs are integrated to cover a wide band from 3000MHz

to 3620MHz and 4000MHz to 4650MHz (direct output), from 1500MHz to 1810MHz and

2000MHz to 2325MHz (selecting divider by 2), from 750MHz to 905MHz and 1000MHz to

1162.5MHz (selecting divider by 4).

VCO A frequency range 3000MHz-3620MHz

VCO B frequency range 4000MHz-4650MHz

VCO Frequency Calibration

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

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

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

An automatic selection of the range is performed when the bit SERCAL rises from "0" to "1".

The charge pump is inhibited and the pins ICP & VCTRL are at VDD/2 volts. Then the ranges

are tested to select the one which with this VCO input voltage is the nearest to the desired

output frequency (Fout = N*Fref/R). When this selection is achieved the signal ENDCALB

(which means End of Calibration) falls to "0", then the charge pump is enabled again and

SERCAL should be reset to "0" before the next channel step. The PLL has just to perform

fine adjustment around VDD/2 on the loop filter to reach Fout, which enables a fast settle.

Figure 19.

VCO Sub-Bands Frequency Characteristics

Charge

Pump

ICP

VCTRL

BUF

VDD

BUF

Cal bit

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