PCI-6800-DBV OVERVIEW
The PCI-6800-DBV is a high-performance, fully tunable BPSK/ QPSK Demodulator, Bit Synchronizer, and Viterbi Decoder for the PCI bus. The board accepts BPSK- or QPSK-modulated carrier or baseband signals, outputting recovered data and clock. Its state-of-the-art design provides bit error performance within 1 dB of theory. Precision tuning (with an ultra-fine 0.012 Hz resolution) and programmable digital filters make the PCI-6800-DBV ideal for multi-carrier applications.

FUNCTIONAL DESCRIPTION
Signals entering the PCI-6800-DBV are routed to the board's analog front-end, which performs signal buffering, source selection, offset compensation, filtering, and amplification (AGC). The conditioned input signal is digitized at 40 million samples per second for input to the Digital Quadrature tuner.

DIGITAL QUADRATURE TUNER
The DQT provides functions required for digital demodulation, including carrier LO generation and mixing, baseband sampling, programmable bandwidth filtering, and AGC control. The DQT outputs complex baseband samples to the Digital Costas Loop (DCL).

DIGITAL COSTAS LOOP
The DCL performs baseband processing tasks, including matched filtering, carrier tracking, bit synchronization, and soft-decision slicing. It provides second order loop filters for carrier tracking and symbol timing recovery. The DCL outputs 3-bit soft symbols and clock to the Viterbi decoder, as well as hard-decision bit data and clock.

VITERBI DECODER
The PCI-6800-DBV Viterbi decoder supports the standard Rate ½, Constraint Length 7 convolutional code. It accepts 3-bit soft symbols at rates up to 10 Msps, outputting recovered bit data and clock. The decoder provides built-in synchronization and bit error rate monitoring circuits.

PCI INTERFACE
Based on the PLX 9050, the PCI-6800-DBV's PCI interface allows host system access to control and status registers via the PCI bus.

INCLUDED SOFTWARE
Avtec provides a Windows application for configuration and monitoring. A Windows driver, DLL and Labview VI library are also available.

Inputs

• Three input sources (software-selectable)
• 0.1 V to 10 Vpp amplitude (w/ auto gain control)
• Up to 10 V offset (built-in offset compensation)
• Normal or inverted polarity
• 50 Ohm or 10 Kohm impedance

Outputs

• Data: NRZ-L, TTL level into 50 Ohms
• Clock: 0 or 180 degree; TTL level into 50 Ohms
• Tape: NRZ-L/M/S, Biphase-L/M/S or RNRZ-L, TTL level into 50 Ohms

PCI Interface

• Based on PLX 9050
• 32-bit, 33 MHz interface for control/status  
• Support for Plug & Play auto-configuration

Demodulator

• 1 KHz to 15 MHz carrier freq. (subcarrier mode)
• 65 to 80 MHz carrier freq. (IF carrier mode)
• BPSK, QPSK, OQPSK demodulation
• Rate: 50 bps-2.5 Mbps (BPSK) or 5 Mbps (QPSK)
• Loop bandwidth: 0.003% to 3% of carrier freq.
• Swept acquisition range w/ programmable limits (% of carrier frequency)
• Tracking range: 10 x loop bandwidth

Bit Synchronizer

• 100 bps to 10 Mbps data rate, with 10 bps low-rate option
• NRZ-L/M/S and Biphase-L/M/S PCM codes
• Loop bandwidth: 0.01% to 2% of data rate
• Tracking range: up to +/- 12% of selected rate

Viterbi Decoder

• Convolutional code: Rate ½, Constraint Length (K) = 7, G1 = 1111001, G2 = 1011011
• Input source: 3-bit soft symbols from Digital Costas Loop or external source
• Symbol rate of up to 10 Msymbols per second
• Coding gain of greater than 5 dB
• Programmable G1/G2 order
• Alternate symbol inversion
• Differential decoding
• Descrambling