RF Quadrature Transceiver / RF Quadrature Receiver
CMX991/CMX992
DOIF
(pin 40)
Output to
Tank Cct
R2
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 3rd 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, b1).
2012 CML Microsystems Plc
18
D/991_992/18
CMLMICRO [ CML MICROCIRCUITS ]
