CMX991 Datasheet, PDF (35/56 Pages) CML Microcircuits – Two-mode demodulator

RF Quadrature Transceiver / RF Quadrature Receiver
CMX991/CMX992
7.3.2 Gain Adjustment
The adjustment of the receiver gain is controlled by b3 – b0 of the Rx Mode Register ($13), see section
6.4.1. The switching of gain during reception of data should be avoided as phase discontinuities will occur
at transitions from –18dB to –24dB and –24dB to –18dB. The architecture of the gain control is shown in
Figure 20.
-48 to -24dB
-18 to 0dB
Figure 20 Receiver Gain Control
7.4 Oscillator Components for Alternative Intermediate Frequencies.
Table 11 shows the tank circuit values for operating the internal IF local oscillator and negative resistance
amplifier at 180MHz (45MHz receive IF). With reference to Figure 13, typical values for other common
intermediate frequencies are shown below.
Receive IF
Frequency
/MHz
NR
Value
VCO
Frequency
/MHz
L1 Value /nH C1 C2 and C3
(Coilcraft Type) Value Value
CV1 and
CV2 Type
10.7
00
42.8
220 (0805CS) 47pF
47pF
SMV1255-
079LF
21.4
00
85.6
100 (0805CS) 18pF
47pF
1SV305
70
00
280
18 (0805CS) 1.2pF 18pF
1SV305
90
00
360
10 (0805CS) 0.8pF 15pF
1SV305
110.5
01
442 §
5.6 (0805CS) 0.5pF 15pF
1SV305
§ NOTE: Above 400MHz reliability of operation under all conditions cannot be guaranteed.
Table 14 Typical IF VCO Circuit Values for a Variety of IF Frequencies
MHz/V
1.25
2.0
6.3
5.9
5.5
 2015 CML Microsystems Plc
35
D/991_992/20