RF Quadrature Transceiver / RF Quadrature Receiver
CMX991/CMX992
The blocking capacitors C1 and C2 may be omitted (i.e point B connected to ground) if the input signals
are 0V dc biased. DC should not be applied to the input pins, otherwise damage to the internal protection
diodes may result.
4.4.2 Transmitter LO Input (CMX991 only)
Exactly the same configuration can be used for the CMX991 Tx LO input as for the receiver (Figure 12,
Table 10). For the transmitter, ‘A’ in the diagram is pin TXLOP and ‘B’ is pin TXLON.
4.5
IF Local Oscillator (CMX991 and CMX992)
A typical configuration for using the internal VCO negative resistance amplifier at 180MHz is shown in
Figure 13. The other external components required to complete the PLL are the loop filter components,
see Figure 14 – which shows a 3rd order loop filter; typical values for a 1kHz bandwidth are given in Table
12.
CMX991
Enable
CMX992
VCO
Negative
Resistance
(NR)
VCO
Output Buffer
Amplifier
Amplifier
Enable
VCOP
VCON
L1
L1 should have
a Q>30
C1
C2
C3
CV2
CV1
R1
R2
Input from
Loop Filter
Figure 13 Example External Components – IF LO VCO External Tank Circuit
L1 33nH (Note 1)
C1 6.8 pF (Note 2)
C2 27 pF
CV1 1S305FCT (Note 3)
CV2 1S305FCT (Note 3)
R1 10kΩ
C3 27 pF
R2 10kΩ
Note 1: Tolerance of 2% or better recommended
Note 2: Tolerance of 5% or better recommended
Note 3: Alternatives are SMV1705-079LF or JDV2S08S (obsolete); SMV1279-079LF gives
increased tuning range and slightly degraded phase noise.
Table 11 IF VCO LO Internal VCO Amplifier Tank Circuit for 180MHz Operation
2012 CML Microsystems Plc
17
D/991_992/18
CMLMICRO [ CML MICROCIRCUITS ]
