rf2059sr RF Micro Devices, rf2059sr Datasheet - Page 13

• Manufacturer Part Number: rf2059sr
• Description: High Performance Rf Pll/vco With Rf Mixers For Wlan Band Shifters
• Manufacturer: RF Micro Devices

The crystal oscillator circuit contains internal loading capacitors. No external loading capacitors are required, dependant on
the crystal loading specification. 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 PCB stray capacitance and oscillator input and output capacitance will also contribute to the
crystal’s total load capacitance. The register settings in the CFG4 register for the switched capacitors are as follows:
The on chip fixed capacitance is approximately 4.2pF.
Wideband Mixer
The RF2059 includes two wideband, double-balanced Gilbert cell mixers. They support RF/IF frequencies of 30MHz to
2500MHz. Each mixer has an input port and an output port that can be used for either IF or RF, i.e. for up conversion or down
conversion. The mixer current can be programmed to between 15mA and 35mA depending on linearity requirements, using
the MIX1_IDD<3:0> word for mixer 1 and the MIX2_IDD<3:0> word for mixer 2, both of which are in the CFG2 register. 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.
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 differential input impedance, and the out-
puts driving 200 differential load impedance. Increasing the mixer output load increases the conversion gain.
The mixer has a broadband common gate input. The input impedance is dominated by the resistance set by the mixer 1/gm
term, which is inversely proportional to the mixer current setting. The resistance will be approximately 85 at the default mixer
current setting (100). There is also some shunt capacitance at the mixer input, and the inductance of the bond wires to con-
sider at higher frequencies.
The mixer output is high impedance, consisting of a resistance of approximately 2k in parallel with some capacitance. The
mixer output does not need to be matched as such, just to see a resistive load. A higher resistance load will give higher output
voltage and gain. A shunt inductor can be used to resonate with the mixer output capacitance at the frequency of interest. This
inductor may not be required at lower frequencies where the impedance of the output capacitance is less significant. At higher
output frequencies the inductance of the bond wires becomes more significant.
For more information about the mixer port impedances and matching, please refer to the RF205x Family Application Note on
Matching Circuits and Baluns.
The mixer layout and pin placement has been optimized for high mixer-to-mixer isolation of typically 60dB. The mixers can be
set up to operate in half-duplex mode (1 mixer active) or full duplex mode (both mixers active). The mode selection is done via
hardware control of the MODE pin and by setting the FULLD bit in the CFG1 register as shown in the table below. When in full-
duplex mode, one can either use PLL register bank 1 or 2, the LO signal is routed to both mixers.
DS100630
• Coarse Tune XO_CT (4 bits) 15*0.55pF, default 0100
• Fine Step XO_CR_S (1 bit) 1*0.25pF, default 0
Mode Pin
High
High
Low
Low
FULLD Bit
0
0
1
1
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at ([phone] or [e-mail].
Active PLL Register Bank
1
2
1
2
Active Mixer
Both
Both
1
2
RF2059
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