CMX972 Datasheet, PDF (28/41 Pages) CML Microcircuits – Small 32-lead VQFN Package

Quadrature Demodulator with IF PLL/VCO
7 Application Notes
7.1 IF/RF Input Matching
CH1 S ₁₁
1 U FS
PRm
Cor
MARKER 1
20 MHz
1_: 990.69
-594.37
13.388 pF
20.000 000 MHz
2_: 455.72
-611.44
45 MHz
3_: 159.09
-383.72
100 MHz
4_: 54.992
-210.29
200 MHz
5_: 40.453
-171.7
250 MHz
1
2
3
4
5
CMX972
START 10.000 000 MHz
STOP 300.000 000 MHz
Figure 14 Quadrature Demodulator Input Impedance (10MHz to 300MHz)
Frequency
(MHz)
20
45
100
200
250
Typical
Impedance
(Ω-/+jΩ)
991 - j594
456 - j611
159 - j384
55 - j210
41 - j172
Parallel Equivalent
Circuit
(R//pF)
1.35kR // 3.5pF
1.28kR // 3.7pF
1.08kR // 3.5pF
860.5R // 3.5pF
768.4R // 3.5pF
Table 15 Quadrature Demodulator Input Impedances and Parallel Equivalent Circuit
The typical input impedance of the IFIN port is shown in Figure 14 and Table 15. The configuration of the
IF input has a significant effect on the measured performance. This is demonstrated in Table 16, where
the receiver is measured with a 50 Ohm source and three different input conditions. A matched network
(e.g. as shown in section 4.2) provides the best noise figure and maximum gain, however intermodulation
will be degraded in this condition due to the larger signal levels indicated by the extra gain. The ‘straight in’
condition means that the 50 Ohm signal source was connected directly at IFIN.
 2015 CML Microsystems Plc
28
D/972/2