ATI Audio DDA124-BNC Manuale operativo e di manutenzione - Pagina 4
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inverted and lights when the clock recovery PLL is in LOCK. The VALIDITY
indicator shows that the previous received sample was valid when transmitted
from the source device. NO ERROR is the absence of any of the other errors and
is good. The SET indicator, used to tune the equalizer adjustment, lights when
the received data eye opening is greater than half a bit period and the recovered
clock is within range.
TRANSMITTERS
The Frame sync (FSYNC), Serial Clock (SCK), Serial audio data (SDATA),
Channel status (C), User channel data (U), and data Validity information (VERF)
are passed directly to the transmitters U9 (U18) for reformatting into the
AES/EBU output data stream TXPA (TXPB). The transmitters are Crystal
Semiconductor CS8404A devices capable of operation from 27 to 96kHz
equivalent sample rates. The transmitters operate in a transparent mode, which
allows the transmitter block structure (Channel Status, User and Validity bits) to
be slaved to the block structure of the receiver. In the transparent mode the
propagation delay of data through the CS8404A is set so that the total
propagation delay from the receiver inputs to the transmitter outputs is exactly
three sample intervals, which is less than 100 microseconds even at the lowest
sample rate.
OUTPUT DRIVERS
BNC outputs are in accordance with the recommendations of AES-3id-1995.
Each side of the differential line driver output U1 and U2 (U5 and U6) is used to
separately drive a 75-ohm capacitor-coupled BNC output. Each BNC output
provides 4Vp-p open circuit thru 75 ohms for a loaded output of 2Vp-p. Although
the two sides of a differential line driver are out of phase with each other there is
no phase difference in the recovered audio since the AES/EBU digital data is
defined only by the presence or absence of transitions. It makes no difference
whether those transitions are hi to low or low to hi.
REFERENCE OSCILLATORS AND POWER SUPPLIES
U10 generates a 6 MHz reference frequency input to U8 (U17) for determining
the incoming frame (sample) rate. The oscillator is counted down in U11, 12, 15
and 16 to provide a synchronized display reset pulse every 3 seconds. U21
generates a precision 2.5VDC reference for the equalizer circuit. U7 and U13
provide regulated and quiet ±5VDC for all circuits. Power transformer primary
windings are paralleled for 115VAC or wired in series for 230VAC. Jumpers E1
allows field modification if necessary.
ATI Audio Inc.
■ Tel: 856-626-3480
■
Fax: 856-504-0220
■
www.
audio.com