PR
EL
IMI
NA
RY
SW71122
MLX71122 RF Receiver
Programming Software Manual
39011 71122 01
Page 16 of 21
SW71122-Manual
Rev. 004
Aug/11
5.3.4
ROCUR
This selection box sets the core current of the reference oscillator. It should not be changed unless there is a
reason to do it.
Four current selections are available: 85
µ
A, 170
µ
A, 270
µ
A, 355
µ
A (default)
5.3.5
PRESCUR
The
PRESCUR
radio buttons specify the bias current of the PLL prescaler. The prescaler is a block that
works at the highest operating frequency of the circuit since it divides the VCO output signal. At high VCO
frequencies and under certain ambient conditions it may be necessary to increase its bias current from the
20
µ
A (default) to 30
µ
A to keep it dividing correctly.
5.3.6
PFDPOL
The polarity of the PDF should not be changed if the standard test circuit is used where only a tank inductor is
placed between pins TNK1 and TNK2. Default value is negative. If the loop filter voltage to frequency charac-
teristic changes the sign of its slope, then it is necessary to change the PDF polarity. This can be the case if
an external VCO is used or if an additional element with controllable reactance is connected between the pins
TNK1 and TNK2.
5.3.7
VCO Range
The MLX71122 is designed for V
CC
= 5V so the default value of this setting is 5V. Nevertheless, it can be
used down to 3V if this value is set to 3V. The most critical part at lower supply voltages is the VCO range
which can be adjusted with this setting. For supply voltages in between, the optimal setting must be found by
experiment.
5.3.8
VCO Buffer Current
The output buffer of the VCO works at the highest operating frequency of the circuit. Since it has to drive the
prescaler with a digital signal, the core current of the buffer can be increased from about 900
µ
A (default) to
1040
µ
A if it is necessary at high VCO frequencies and under certain ambient conditions.
5.3.9
VCO Core Current
The VCO core works at the highest operating frequency of the circuit. Its core current can be increased from
about 450
µ
A (default) to 520
µ
A if it is necessary at high VCO frequencies and under certain ambient
conditions.