CMX991 Datasheet, PDF (17/56 Pages) CML Microcircuits – Two-mode demodulator

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 3^rd order loop filter; typical values for a 1kHz bandwidth are given in Table
12.
Enable
CMX991
CMX992
VCO
Negative
Resistance
(NR)
Amplifier
VCO
Output Buffer
Amplifier
VCOP
L1
VCON
C1
Enable
L1 should have
a Q>30
C2
C3
CV1
CV2
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
C3 27 pF
CV1 1SV305 (Note 3)
CV2 1SV305 (Note 3)
R1 10kΩ
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); SMV1249-079LF gives
increased tuning range and slightly degraded phase noise.
Table 11 IF VCO LO Internal VCO Amplifier Tank Circuit for 180MHz Operation
 2015 CML Microsystems Plc
17
D/991_992/20