1. Introduction to the HDM8513A
The HDM8513A digital demodulator for direct broadcast satellite receivers is a single chip solution fully
compliant with the European Telecommunications Standards Institute (ETSI) specification ETS 300
421. This chip integrates an A/D converter, a variable rate matched filter, a variable rate QPSK
demodulator with a Viterbi decoder, a deinterleaver and a Reed Solomon decoder.
The HDM8513A, which is implemented in a 0.35 micron CMOS, Triple Layer Metal Process, provides
variable rate capability while operating with a fixed frequency sampling clock. Digital samples of
baseband I and Q data are generated by an internal A/D converter, then provided to the demodulator at
a fixed sample rate. The root raised cosine filter is implemented internally with fully digital techniques.
Similarly, the symbol timing recovery and carrier phase tracking functions are performed entirely in the
digital domain. This approach provides minimum constraints on external circuits, thus reducing overall
system costs.
The HDM8513A may be configured by an external processor for a specific symbol rate, and carrier
frequency along with loop gain parameters. The HDM8513A provides an external AGC signal which is
used to control the gain of the analog signal which is applied to the down-converters. And it also
provides a digital AGC internally which controls the gain of the signal out of the matched filters. In
addition, the HDM8513A provides fully programmable sweep circuitry to aid in initial acquisition when
large frequency offsets may be present.
The digital frequency translation capability of the HDM8513A permits this part to be used in frequency
multiplexing applications. In this application, an entire transponder bandwidth containing many signals
is sampled at a fixed rate. The digital oscillator within the HDM8513A is programmed to the specific
desired carrier frequency within that band to permit the selected signal to be passed through the
baseband filter and processed by the demodulator circuits.
Fixed Rate
Sample Clock
Symbol Clock
6
3
Viterbi Bit Clock
Data Clock
I
Q
A/D
Converter
6
Variable
Rate
QPSK
Demodulator
3
Viterbi
Decoder
Synchronization
and
Deinterleaving
8
Reed
Solomon
Decoder
8
Data
Frame
Sync
QPSK
Lock
Node
Sync
Viterbi
Data
F
IGURE
1: T
OP
L
EVEL
B
LOCK
D
IAGRAM
6
HYNIX [ HYNIX SEMICONDUCTOR ]
