Comtech EF Data DMD1050 - Manual (Page 28)

DMD1050 Satellite Modem Board Theory of Operation
MN-DMD1050 3–2
Revision 9
3.1.1 DMD1050 L-Band Printed Circuit Card
The L-Band/IF Printed Circuit Card consists of an analog modulation function, an analog
complex down conversion, and two wide-band digital synthesizers. The block diagram of the L-
Band Assembly is shown in Figure 3-2.
Figure 3-2. L-Band Assembly
In the modulator, analog in-phase (I) and quadrature (Q) signals are generated on the Digital
Baseband Printed Circuit Card, routed to the L-Band Printed Circuit Card, and modulated at the
desired frequency. The L-Band modulated signal is then passed through a microprocessor
controlled variable attenuator providing gain control of the output signal.
In the complex downconverter, the signal for demodulation is amplified and sent through a
variable wideband attenuator for AGC. The gain-controlled signal is then passed through a
complex downconverter to a low IF.
3.1.2 DMD1050 Baseband Processing Printed Circuit Card
The advent of million-plus gate count FPGAs, advanced logic synthesis tools, and DSPs
providing hundreds of MIPs enabled the design of a software configurable modem. Large, fast
FPGAs now provide designers with what is essentially an on the fly programmable ASIC. High
speed, complex digital logic functions that previously could only be implemented in dedicated
integrated circuits are now downloaded from a micro-controller through a serial or peripheral
interface. When a new digital logic function is needed, a new configuration file is loaded into the
Quadrature
Demodulator
IF Board Connector
(40
-Pin Header
)
Demodulator I
Demodulator I Inv.
Demodulator Q
Demodulator Q Inv.
AGC
L-Band
Synthesizer
PDA
Analog Q Inv.
Analog I Inv.
L-Band
Synthesizer
Quadrature
Modulator
Analog Q
Analog I
LPF
LPF
Switch
RxLB
TxLB
Coupler
DCSA