CMX994 Datasheet, PDF (32/61 Pages) CML Microcircuits – Local Oscillator

Direct Conversion Receivers
CMX994/CMX994A/CMX994E
7.8
7.8.1
Extended Rx Offset Register – CMX994A and CMX994E only
Extended Rx Offset: $17 – 16-bit write only
All bits of this register are cleared to ‘0’ by a General Reset command.
Note 1: the bits in registers $13 and $17 control the same hardware functions with the most recent write to
$17 or $13 being applicable at any given time; if $13 is written then QDC5, QDC4, IDC5 and IDC4 will
automatically be set to ‘0’.
Note 2: QDC3 and IDC3 have different function in $13 and $17; in $13 QDC3 and IDC3 sets the correction
polarity whereas in $17 the polarity is set by QDC5 and IDC5.
15
14
13
12
11
10
9
8
0
0
QDC5
QDC4
QDC3
QDC2
QDC1
QDC0
7
6
5
4
3
2
1
0
0
0
IDC5
IDC4
IDC3
IDC2
IDC1
IDC0
b13-8,
b5-0 I/Q DC Offset correction; see section 6.2.1
The values in the table below are the effects of the offset at the maximum VGA gain (minimum
attenuation) setting. They are proportionately lower for lower gain settings (as set by the Rx Gain
Register (b2 – b0). The aim of this Rx Offset Register is to allow output offsets to be reduced
sufficiently (typically <25mV) to avoid any significant reduction in the dynamic range of any
subsequent ADC. It is expected that demodulation software in the baseband processor would be
required to correct for the remaining offset as part of the demodulation process. See also section
8.1.2
b5 b4 b3 b2 b1
b13 b12 b11 b10 b9
1 1 1 11
1 1 1 11
1 0 0 10
1 0 0 10
1 0 0 01
1 0 0 01
1 0 0 00
1 0 0 00
0 1 1 11
0 1 1 11
0 0 0 11
0 0 0 11
0 0 0 10
0 0 0 10
0 0 0 01
0 0 0 01
0 0 0 00
0 0 0 00
b0 I Channel at maximum gain
b8 Q Channel at maximum gain
1 -775mV
0 -750mV
etc. (i.e. binary count, step 25mV)
1 -125mV
0 -100mV
1 -75mV
0 -50mV
1 -25mV
0 No correction
1 +775mV
0 +750mV
etc. (i.e. binary count, step 25mV)
1 +175mV
0 +150mV
1 +125mV
0 +100mV
1 +75mV
0 +50mV
1 +25mV
0 No correction
7.8.2 Extended Rx Offset: $E7 – 16-bit read only
This read-only register mirrors the value in register $17; see section 7.8.1 for details of bit functions.
 2015 CML Microsystems Plc
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