CMX972 Datasheet, PDF (9/41 Pages) CML Microcircuits – Small 32-lead VQFN Package

Quadrature Demodulator with IF PLL/VCO
CMX972
4.2 Quadrature Demodulator
The input impedance of the quadrature demodulator section is shown in section 7.1. The input can be
driven from a 50 Ohm source or can be matched to 50 Ohms. A typical 50 Ohm matching circuit is shown
in Figure 3 for operation at 45MHz.
IF Input
CMX972
L1
IFIN
C1
Figure 3 IF Input Match Circuit
L1
910nH
C1
10pF
Table 3 Quadrature Demodulator Input Components
4.3 Local Oscillator (LO) Input
The CMX972 has a single-ended LO input. The demodulator LO can come from either the on-chip
VCO/PLL or from an external source (RXLO pin), see section 5.3.
Users should be aware that the presence of high levels of harmonics in the signals applied to the RXLO
input might degrade quadrature accuracy.
RXLO Input
CMX972
Buffer and
Divider
Figure 4 RXLO Input Configuration
4.4 VCO and PLL
A typical configuration for using the internal VCO negative resistance amplifier at 180MHz is shown in
Figure 5. The other external components required to complete the PLL are the loop filter components, see
Figure 6 – which shows a 3^rd order loop filter; typical values for a 300Hz bandwidth are given in Table 5.
 2015 CML Microsystems Plc
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