AIS Baseband IC with/without RF Synthesiser
CMX7032/CMX7042
30 tick fixed delay
2
10
10
17
10
0
3
7
5
B
Modulation at Input to the
Tx Filters
Last
bit
Modulation at the
Mod 1 & 2 Output
Last
bit
20 tick Tx filter delay
Time
Figure 13 Typical AIS Transmission
Table 8 Example Tx Event Sequence Setup
Parameter
Event ID delay
total
Explanation
Insert 10 tick delay then start monitoring the chosen Rx
input for a signal which may cause an abort (if CSTDMA
enabled).
CSTDMA_START
1
10
20
Insert 17 tick delay then start feeding data to the transmit
modulator and filters (this allows for the 20 tick storage
delay in the Tx filters so that modulated data appears at
the end of the RAMDAC ramp_up period – tick 47).
MODULATE_START
5
17
37
CSTDMA_END
Tx_en_hi
2
3
10
0
47
47
Insert 10 tick delay then stop CSTDMA monitoring.
Set TXENA line high (assuming not aborted)
Insert 3 tick delay then initiate the RAMDAC ramp-up (for
AIS, the transmitted signal will be carrier only at this
point)
RAMDAC_UP
4
3
50
At this point during a transmission the CMX7032/CMX7042 feeds the entire message to the transmit modulator bit-
by-bit. All subsequent transmit events are timed relative to the end of the last message bit, indicated by the
MODULATE_END event.
RAMDAC_DOWN
7
8
6
0
7
5
0
Initiate the RAMDAC ramp-down immediately
Insert 7 tick delay (to allow RAMDAC to fully ramp down)
then set the TXENA line low.
Tx_en_lo
7
MODULATE_END
12
Allows for process delays.
Notes:
1. It is essential that the CSTDMA, and MODULATE START events precede their associated END events,
otherwise undesirable results will be obtained.
2. MODULATE_START must appear in the first group of timed events (table entries 1–5), MODULATE_END must
appear in the final group (table entries 6-8). It is feasible to place the RAMDAC_DOWN task before the
MODULATE_END task.
Assuming that the timing_start value has been set to 10 (see User Manual section 9.19.2.7) and the RAMDAC is
set to its default values (312us), this sequence approximates to the Class B CSTDMA timing with ideal hardware
(RAMDAC starts 20bits / 50 ticks after SLOTCLK).
7.6.6 Modulation Formats
The CMX7032/CMX7042 can be configured to drive either a two-point VCO and Reference modulator or
an I/Q modulator by selecting the appropriate Config task (see User Manual section 9.19.2.1).
Typical Tx spectrum plots for both modes are shown below (generated by modulating a signal generator
with the outputs of MOD1 and MOD2 and then analysing the signal on a spectrum analyser). Note that
these plots represent the steady-state transmission and so are shown with the Class A and Class B-
SOTDMA spectrum mask (-70dBc). The Class B–CSTDMA standard specifies a slotted transmission with
a mask at –60dBc.
2012 CML Microsystems Plc
37
D/7032/42_FI1.2/13
CMLMICRO [ CML MICROCIRCUITS ]
