CMX994 Datasheet, PDF (42/61 Pages) CML Microcircuits – Local Oscillator

Direct Conversion Receivers
CMX994/CMX994A/CMX994E
14
Gain
12
10
8
6
4
IIP3
2
8.1.5
8.1.6
0
0
10
20
30
40
50
60
IM Reg setting / dec
Figure 21 Variation of LNA Gain and IMD with IM Register Setting, 450 MHz
Low Power Mode
If the low power mode is enabled, General Control Register ($11) b4 = 1, the total current drawn in the
receiver section reduces by approximately 10mA. For indications of the performance changes in low power
mode; see section 8.1.1.
The IP2 performance in low power mode varies with frequency. Below 400MHz the average change between
normal mode and low power mode is small. Above 400MHz low power mode causes an increasing
degradation reaching 15dB (typical) at maximum operating frequency. Around 450MHz the degradation is
typically 2 to 5 dB. As is usual with IP2 measurements, variations in measured values are observed at
different frequency offsets, between I and Q channels and between devices, so average values must be
considered.
The CMX994A/CMX994E has other low power modes that are enabled using the Options Control Register
($15). Power can be reduced by disabling the phase correction circuits ($15 = $03) if the excellent I/Q balance
provided by the CMX994A/CMX994E is not needed. Another option is to disable either I or Q path; this facility
is useful for minimising power when monitoring a channel for a RF signal.
I/Q Filter Response
The I/Q filter has a well-defined response and an internal calibration scheme makes it very stable with
temperature. The response with temperature, measured through the entire receiver, is shown in Figure
22(a). It will be observed that, apart from a small change in overall gain, the filter response does not vary. The
scaling with ACR Flt bits (Rx Control Register ($12), b4-b3) is shown in Figure 22(b).
55.00
5
3
50.00
1
Room
+55degs
45.00
+85degs
-1
-20degs
-40degs
40.00
-3
35.00
-5
-7
30.00
-9
-11
-13
-15
100
25.00
20.00
1000
Frequency (Hz)
10000
(a)
100000
15.00
0.1
Figure 22 I/Q Filter Response
 2015 CML Microsystems Plc
Page 42 of 70
1
10
Freq (kHz)
(b)
MAX BW
MID BW
MIN BW
100
D/994_A_E/1