RF Quadrature Transceiver / RF Quadrature Receiver
CMX991/CMX992
7.5
RF Mixer Input Matching
With reference to Figure 21 and Table 15 below, the receiver input can be matched to alternative
frequencies, with typical values shown. In all cases, R1, R2 = not fitted and C3, C4 = 1nF.
R1
CMX991/992
L1
C3
C4
R3
Input
MIXINP
MIXINN
T1
L2
C1
R2
Figure 21 Receiver Matching Components
Component
L1
L2
100MHz
220nH
2.7pF
155MHz
150nH
Not fitted
850MHz
0R
4.7nH
(0603)
6.8pF
950MHz
0R
6.8nH
(0603)
3.9pF
R3
C1
0R
Not fitted
0R
4.7pF
Not fitted
Not fitted
Table 15 Receiver Input Match Circuit for Other Operating Frequencies
7.6
RF Mixer IF Output Matching
In a typical implementation, the MIXOUT pin(s) will require matching from around 500Ω ║ 4pF to the input
of a crystal filter. The impedance of such a filter will often only be specified within the passband; it will be
very different outside the passband. Careful broad band termination of the MIXOUT port is therefore
critical in achieving the optimum intermodulation and spurious response performance from the system.
The use of a shunt resistive element at MIXOUT is a compromise between system gain and
intermodulation. Values between 1,000ohms and 120ohms can be used in practice. Some shunt
capacitance at MIXOUT also helps in suppressing harmonics of the RF and LO inputs that may appear at
the port, so a Pi network is recommended.
With the matching network of Figure 7, the rejection of the half IF response has been found to be optimum
using high side mixing.
2012 CML Microsystems Plc
36
D/991_992/18
CMLMICRO [ CML MICROCIRCUITS ]
