CMX991 Datasheet, PDF (23/56 Pages) CML Microcircuits – Two-mode demodulator

RF Quadrature Transceiver / RF Quadrature Receiver
CMX991/CMX992
f_out = f_ref x ( N / M )
where
f_out = The desired output frequency in MHz
f_ref = 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.
CH1 S ₁₁
1 U FS
PRm
C?
Del
CH2 S ₁₁
log MAG
PRm
C?
SCALE
1 _{5 dB/div}
1_ 100.5
26 Feb 2009 17:19:44
-284.67
5.5908 pF
100.000 000 MHz
2_ 35.797
-100.45
450 MHz
3_ 23.598
-64.363
1
820 MHz
4_ 22.861
-48.746
1 GHz
43 ²
5 dB/
2
REF 0 dB
1_:-.9361 dB
100.000 000 MHz
2_:-2.2931 dB
450 MHz
3_:-2.9567 dB
820 MHz
4_:-3.9252 dB
1 GHz
3
4
START 100.000 000 MHz
STOP 1 200.000 000 MHz
Figure 18 Typical LO Input Impedance
 2015 CML Microsystems Plc
23
D/991_992/20