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RF2054

DS120320

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

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

Detailed Description

The RF2054 is a frequency converter chip that includes a fractional-N phase locked loop, a low noise VCO core, an LO signal

multiplexer, two LO buffer circuits, and two RF mixers. Synthesizer programming, device configuration, and control are

achieved through a mixture of hardware and software controls. All on-chip registers are programmed through a simple three-

wire serial interface.

VCO

The VCO core in the RF2054 consists of one VCO which covers a frequency range dependant on the value of the external

inductor used. The RF2054 has been characterized with 3.3nH inductors, so the VCO covers from 940MHz to 1000MHz. Note

that the VCO inductor is differential so the value given is the inductance on each device pin, and the total differential induc-

tance will be twice this value.

VCO3 must be selected using the PLL1x0:P1_VCOSEL and PLL2x0:P2_VCOSEL control word and setting 10 for VCO3. The VCO

has 128 overlapping bands to achieve an acceptable VCO gain (MHz/V) and hence a good phase noise performance across

the whole tuning range. The chip automatically selects the correct VCO band (VCO coarse tuning) to generate the desired fre-

quency based on the values programmed into the PLL1 and PLL2 register banks. For information on how to program the

desired LO frequency into the PLL1 and PLL2 banks, refer to the next section. The automatic VCO band selection is triggered

every time the ENBL pin is taken high. Once the band has been selected, the PLL will lock onto the correct frequency. During

the band selection process, fixed capacitance elements are progressively connected to the VCO resonant circuit until the VCO

is oscillating at approximately the correct frequency. The output of this band selection is made available in the RB1:CT_CAL

read-back register. A value of 127 or 0 in this register indicates that the selection was unsuccessful; this is usually due to the

wrong VCO being selected so the user is trying to program a frequency that is outside of the VCO operating range. A value

between one and 126 indicates a successful calibration, the actual value being dependent on the desired frequency, as well

as process variation. The band selection takes approximately 25

s with a 21MHz clock. The band select process will center

the VCO tuning voltage at about 1.0V, compensating for manufacturing tolerances and process variation, as well as environ-

mental factors, including temperature. For applications where the synthesizer is always on and the LO frequency is fixed, the

synthesizer will maintain lock over the whole temperature range of -20°C to +75°C. However, it is recommended to re-initiate

an automatic band selection for every 30 degrees of temperature change in order to maintain optimal synthesizer perfor-

mance. This assumes an active loop filter. If start-up time is a critical parameter and the user is always programming the same

frequency for the PLL, the calibration result may be read back from the RB1:CT_CAL register and written to PLL1x2:P1_CT_DEF

or PLL2x2:P2_CT_DEF registers (depending on the desired PLL register bank). The calibration function must then be disabled

by setting the PLL1x0:P1_CT_EN and/or PLL2x0:P2_CT_EN control words to 0. For further information, please refer to the

RF205x Calibration User Guide.

The LO divide ratio is set by the PLL1x0:P1_LODIV and PLL2x0:P2_LODIV control words. The LO is routed to mixer1, mixer2, or

both, depending on the state of the MODE pin and the value of CFG1:FULLD.