STW81101AT datasheet(19/42 Pages) STMICROELECTRONICS

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STW81101

General description

19/42

Figure 14.

Loop filter connection

4.1.8

Voltage controlled oscillators

VCO Selection

Within STW81101 two low-noise VCOs are integrated to cover a wide band from 3300MHz

to 4400MHz (direct output), from 1650MHz to 2200MHz (selecting divider by 2) and from

825MHz to 1100MHz (selecting divider by 4).

VCO A frequency range 3300MHz-3900MHz

VCO B frequency range 3800MHz-4400MHz

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 15.

VCO Sub-Bands Frequency Characteristics

Charge

Pump

ICP

VCTRL

BUF

VDD

BUF

Cal bit

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