CMX994 Datasheet, PDF (41/61 Pages) CML Microcircuits – Local Oscillator

Direct Conversion Receivers
CMX994/CMX994A/CMX994E
Gain Setting
Gain Cntrl Step
Size (dB)
Cumulative
Gain Change
(dB)
Variation
from
Nominal
(dB)
Nominal step size
Max
0.0
-6 dB
-12 dB
-18 dB
-6.4
-6.4
-0.4
-5.6
-12.0
0.0
-5.2
-17.2
0.8
Nominal +0.7 dB
Max
0.0
-6 dB
-6.4
-12 dB
-7.1
-18 dB
-5.6
0.0
-6.4
-0.4
-13.5
-1.5
-19.1
-1.1
Nominal +1.4 dB
Max
-6 dB
-6.4
-12 dB
-8.6
-18 dB
-5.7
0.0
-6.4
-0.4
-15.1
-3.1
-20.7
-2.7
8.1.4
Nominal +2.8 dB
Max
-6 dB
-12 dB
-18 dB
-6.5
-10.3
-5.5
0.0
-6.5
-0.5
-16.8
-4.8
-22.3
-4.3
Table 17 Typical LNA Gain Step Sizes at 940MHz, Z_O=50Ω
LNA Intermodulation Optimisation
The intermodulation (IMD) performance of the LNA can be optimised using the IM bits in the IM Control
register ($14); see section 7.5.1.
At higher frequencies, typically 400MHz and above, optimum IMD performance is with the IM bits set to
maximum, i.e. 0x3F. The improved IMD performance comes with a reduction in gain of approximately 0.5dB;
see Figure 21.
At minimum frequency (circa 100MHz) the IM bits should be set to minimum i.e. 0x00.
 2015 CML Microsystems Plc
Page 41 of 70
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