CMX991 Datasheet, PDF (18/56 Pages) CML Microcircuits – Two-mode demodulator

RF Quadrature Transceiver / RF Quadrature Receiver
CMX991/CMX992
DOIF
(pin 40)
Output to
R2
Tank Cct
R1
C1
C3
C2
Figure 14 Example External Components – IF LO Loop Filter
C1 22nF
C2 470nF
C3 1nF
R1 430Ω
R2 12kΩ
Table 12 IF LO 3^rd Order Loop Filter Circuit for 180MHz Operation
To inject an external IF LO signal, the negative resistance amplifier should be disabled, with the VCON
input decoupled to ground with a 1nF capacitor. The signal is then applied to VCOP via a dc blocking
capacitor (e.g. 1nF). Other circuitry shown above, such as the tank circuit, should be not fitted.
Note: When using an external IF VCO the N divider can experience a transient during start up that will
cause incorrect operation (charge pump always ‘high’). To avoid this situation either the value of the PLL N
divider should be an integer multiple of 4 or it is necessary to ensure that the external VCO is powered-up
before the PLL is enabled (register $21, b7).
 2015 CML Microsystems Plc
18
D/991_992/20