RF Quadrature Transceiver / RF Quadrature Receiver
CMX991/CMX992
fout = fref x ( N / M )
where
fout = The desired output frequency in MHz
fref = The reference frequency supplied to the PLL on pin FREF in MHz
N = Divider value programmed in the N divider register (see section 6.9.1)
M = Divider value programmed in the M divider register (see section 6.8.1)
The PLL only supports VCOs with a positive tuning slope, i.e. a high tuning voltage from DO results in a
higher oscillation frequency from the VCO.
The PLL has a lock-detect function that can be evaluated using register $21, b6 (section 6.8.2).
The VCO amplifier is a negative resistance amplifier requiring an external tank circuit (see section 4.5).
The amplifier has two control bits available in the general control register (section 6.2, register $11, b2 -
b3). These bits can be used to optimise performance for a particular tank circuit depending on its Q value.
5.4.2 RF Local Oscillator
The main LO for both the transmitter and the receiver are not provided on the CMX991/CMX992 and must
be supplied from an external source (see section 4.4). Independent selectable internal dividers for Tx and
Rx sections are provided to work with the external source, see Figure 3 or Figure 4. The input impedance
is nominally 300Ω differential with a series capacitance of 6pF to each pin.
26 Feb 2009 17:19:44
CH1
S
1 U FS
1_ 100.5
-284.67
5.5908 pF
11
100.000 000 MHz
PRm
C?
2_ 35.797
-100.45
450 MHz
3_ 23.598
-64.363
820 MHz
Del
1
4_ 22.861
-48.746
1 GHz
2
4
3
CH2
S
log MAG
5 dB/
REF 0 dB
1_:-.9361 dB
100.000 000 MHz
11
PRm
C?
2_:-2.2931 dB
450 MHz
SCALE
5 dB/div
3_:-2.9567 dB
820 MHz
1
4_:-3.9252 dB
1 GHz
2
3
4
START 100.000 000 MHz
STOP 1 200.000 000 MHz
Figure 18 Typical LO Input Impedance
2012 CML Microsystems Plc
23
D/991_992/18
CMLMICRO [ CML MICROCIRCUITS ]
