CMX7163 QAM Modem
CMX7163
7.4.10 The Transmit Sequence
The CMX7163 is capable of being configured to provide the following features:
1. Selecting Tx mode results in transmission starting directly on entry to Tx mode or is delayed until
GPIOA is used as an input trigger
2. Selecting carrier sense mode will result in behaviour as in point 1, followed by a carrier sense
period, where transmission is delayed (reception continues) until a carrier sense period is
completed and no activity is sensed on the channel
3. Selecting Tx calibration will cause CMX998 cartesian loop dc calibration to be carried out prior to
transmission, as part of the programmable transmit sequence. See section 7.4.11 CMX998 DC
Offset Calibration for details.
4. Once started, transmission can be configured to be a simple modulation output or can include a
programmable sequence of events including RAMDAC ramp up/down and GPIO On/Off.
Each of these operations can be selected independently of the others. The following diagram
illustrates transmit operation.
Time
Modem
Mode =
Control Mode
Mode = CS or Tx
Rx
Reception
Active (High)
Active if mode=CS, Inactive if
mode=Tx
Carrier Sense
Tx Trigger Input
(GPIOA)
Tx on Outputs
(GPIOA-D)
RAMDAC
Output
Preamble/
Sync
Data
Payload
Tail
Bits
Modulation
Out
Transmit
Calibration
Cal
Carrier Sense -
Awaiting Tx
CMX
998
DC
offset
Cal.
if selected may
Trigger on
Transmit Sequence –
RAMDAC and GPIO
on/off if configured
Pre-Tx, in
Receive
cause abort to
GPIOA, if
Tx Ended
Rx at any
point.
Configured
Figure 15 Transmit Sequence
7.4.11 CMX998 DC Offset Calibration
The CMX7163 may be interfaced to a CMX998 Cartesian Loop IC. The CMX998 is used to provide
linearisation of the power amplifier used to transmit the modulation produced by the CMX7163. If the
signal produced by the CMX7163 when no modulation is present does not exactly match the dc reference
of the CMX998, carrier leakage will result. This worsens the transmitted signal quality. DC offset
calibration is intended to significantly reduce the carrier leakage.
2014 CML Microsystems Plc
Page 34
D/7163_FI-4.x/12
CMLMICRO [ CML MICROCIRCUITS ]
