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RFFC5061/62

DS110614

7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical

support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.

The synthesizer step size is typically 1.5Hz when using a 26MHz reference frequency. The exact step size for any reference

and LO frequency can be calculated using the following formula:

divider value.

Pin 26 (GPO4) can be configured as a lock detect pin. The lock status is also available in the read-back register. The lock detect

function is a window detector on the VCO tuning voltage. The lock flag will be high to show PLL lock which corresponds to the

VCO tuning voltage being within the specified range, typically 0.30V to 1.25V.

Phase Detector and Charge Pump

The phase detector provides a current output to drive an active loop filter. The charge pump output current is set by the value

contained in the P1_CP_DEF and P2_CP_DEF fields in the loop filter configuration register. The charge pump current is given

by approximately 3uA/bit, and the fields are 6 bits long. This gives default value (31) of 93uA and maximum value (63) of

189uA.

If the automatic loop bandwidth calibration is enabled the charge pump current is set by the calibration algorithm based upon

the VCO gain.

The phase detector will operate with a maximum input frequency of 26MHz.

Loop Filter

The active loop filter is implemented using the on-chip low noise op-amp with external resistors and capacitors. The internal

configuration of the chip is shown below with the recommended active loop filter. The op-amp gives a tuning voltage range of

typically +0.1V to +2.4V. The recommended loop filter shown is designed to give the lowest integrated phase noise for refer-

ence frequency of 26MHz. The external loop filter gives the flexibility to optimize the loop response for any particular applica-

tion and combination of reference and VCO frequencies.

Crystal Oscillator

The RFFC5061 and RFFC5062 have been designed to use a standard, low cost, external crystal of typically 26MHz. The crystal

oscillator circuit contains internal loading capacitors. No external loading capacitors are required, assuming crystal load speci-

fication of between 8pF and 10pF.

The internal loading capacitors are a combination of fixed capacitance, and an array of switched capacitors. The switched

capacitors can be used to tune the crystal oscillator onto the required center frequency and minimize frequency error. The

capacitance steps are approximately 0.25pF (fine) and 0.55pF (coarse) and the total differential capacitance range is from

LFILT1

8p2

180p

22K

470R

470R

330p

330p

LFILT2

LFILT3

+1.1V