User's Manual

8.2 Audio / Video Encoder
The Encoder board consists of the following main functions:
• SDI to Digital deserializer. Converts the SMPTE-259M-C serial digital video input
to an 8 bit parallel digital video bus.
• Analogue to Digital Video Converter, 10-bit over sampling ADC. Takes either
Composite Video (75 Ω, 1v p-p) (CVBS); YC or YUV inputs in either PAL / NTSC
format or converts to an 8-bit parallel digital video bus.
• Analogue to Digital Audio Converter, 48kHz, 24 bit
Two high impedance analog inputs. Audio 1 (or left channel). Audio 2 (or right
channel). The two channels are first buffered by a variable gain stage to cater for
either Mic or Line level inputs. A switchable 20dB stage is also included to cater for
low level Mic inputs. The two audio channels are then converted into an I
2
S serial
data stream.
• FPGA. Selects the required 8 bit-parallel digital video bus from either the SDI
deserializer or the video ADC for input to the MPEG2 encoder. A relay is used to
route the input from the BNC (either SDI or CVBS) to either the deserializer or
ADC. Selects the I
2
S from the ASE/EBU receiver or the audio ADC for input to the
MPEG2 encoder. Generates the video test bars and audio test tones.
• Microcontroller. Writes control data and reads status data to/from the MPEG2
Encoder.
• MPEG2 Encoder
A suite of MPEG2 compliant compression techniques, where the data bit rate is
reduced by processing over multiple picture frames. The absolute picture (Intra
frame) is interleaved with pictures that are created using difference data (Predicted
frame) with Bi-directionally predicted frames (4:2:2 Only) in conjunction with motion
compensation; thus low data rates down to 6 Mbps, can be achieved.
A set of encoding parameters is loaded into the encoder at power up. These are
selected from one of the ‘preset’ encoder memories. See 5.6
• DC Power Supplies
Switching DC/DC converters are used to generate the various supplies from the
incoming 9-18V battery supply. These include 2.5, 3.3V, 5V, 8V and +/-5V
supplies.
There are no field replaceable parts on the Encoder board. If a fault occurs with the board,
contact RF Central for technical assistance.
RFX-PHT/CMT Issue 1.1 Page 29 of 33