CMX991 datasheet(17/56 Pages) CMLMICRO

17 / 56 page

RF Quadrature Transceiver / RF Quadrature Receiver

CMX991/CMX992

 2015 CML Microsystems Plc

D/991_992/20

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.

CMX991

CMX992

CV1

VCO

Negative

Resistance

(NR)

Amplifier

CV2

VCOP

VCON

L1 should have

a Q>30

Input from

Loop Filter

VCO

Output Buffer

Amplifier

Enable

Figure 13 Example External Components

– IF LO VCO External Tank Circuit

33nH (Note 1)

CV1

1SV305 (Note 3)

6.8 pF (Note 2)

CV2

1SV305 (Note 3)

27 pF

10k

27 pF

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

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