rf2052 RF Micro Devices, rf2052 Datasheet - Page 8

• Manufacturer Part Number: rf2052
• Description: High Performance Wideband Rf Synthesizer/vco With Integrated Rf Mixer
• Manufacturer: RF Micro Devices

RF2052
The RF2052 includes a wideband fractional-N phase-locked loop, an op-amp to enable an active loop filter (if required), a wide-
band frequency generation (VCO) capability, a wideband mixer, and a low-noise crystal oscillator circuit.
A true 3-wire serial interface is provided for synthesizer programming, device configuration and control. Various diagnostic indi-
cators are also available using the read function of the serial bus if required. Hardware controls for power-down and mixer
selection are also provided.
Wideband Mixer
RF2052 includes a wideband mixer. It supports RF/IF frequencies of 50MHz to 2500MHz using the internal VCO to provide the
LO frequency of 300MHz to 2400MHz. The mixer has in input port and an output port that can be used for either the IF or the
RF ports. The mixer current can be programmed allowing a trade-off between power consumption and linearity. The majority of
the mixer current is sourced through the output pins via either a centre-tapped balun or an RF choke in the external matching
circuitry to the supply. This can be programmed to between 5mA and 20mA depending on linearity requirements, using the
MIX2_IDD<3:0> word in the CFG2 register.
The RF mixer input and output ports are differential and require simple matching circuits optimized to the specific application
frequencies. A conversion gain of approximately -3dB to 0dB is achieved with 100 Ω differential input impedance, and the out-
puts driving 500 Ω to 50 Ω differential impedance match at the pins.
VCO
In the RF2052 three VCOs are used to cover the whole tuning range requirement. VCO1 uses an integrated inductor, and is
optimized for use between 1972MHz and 2400MHz. VCO2 also has an internal inductor and is optimized for use between
1556MHz and 1972MHz. The third, low frequency, VCO uses an external strip-line resonator that may be configured by the
user, but which is intended for use between 1200MHz and 1556MHz. The VCO is selected using the P1_VCOSEL<1:0> and
P2_VCOSEL<1:0> control words in the PLL1x0 or PLL2x0 registers (depending on mode). The VCO current may also be pro-
grammed using the P1_VCOI or P2_VCOI control words in the PLL1x1 and PLL2x1 registers respectively. This allows optimiza-
tion of VCO performance for a particular frequency. A divide-by 1/2/4 block follows the VCO, to allow a LO frequency from
300MHz to 2400MHz to be obtained. The divide ratio is set by the P1_LODIV<1:0> and P2_LODIV<1:0> control words in the
RxPLLx0 and TxPLLx0 registers.
Fractional-N PLL
The IC contains a charge-pump based, fractional-N phase locked loop (PLL) for controlling the three VCOs. The PLL includes
automatic calibration systems to counteract the effects of process and environmental variations, ensuring repeatable lock-
time and noise performance. The PLL is intended to use a reference frequency signal of 10MHz to 104MHz. A reference
divider (divide by 1, 2, or 4) is supplied and should be programmed to limit the frequency at the phase detector to a maximum
of 52MHz.
The PLL will lock the VCO to the frequency F
where N is the programmed fractional N divider value consisting of N and NUM, F
OSCA pin, and R is the programmed R divider value (1, 2, or 4).
The N divider is a fractional divider, containing a dual-modulus prescaler and a digitally spur-compensated fractional sequence
generator to allow fine frequency steps. The N divider is programmed using the N(9:0) and NUM(23:0) bits as follows:
First determine the desired, effective N divider value, N
N(9:0) should be set to the integer part of N
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EFF
VCO
. NUM should be set to the fractional part of N
Detailed Description
according to:
F
N
VCO
EFF
EFF
=2*N*F
:
=F
VCO
*R/F
OSC
Preliminary
OSC
/R
OSC
is the reference signal frequency at the
EFF
multiplied by 2
24
Prelim DS080513
=16777216.