Grass Valley 8920ADC v.2.0.1A - Manual (Page 35)

8920ADC Instruction Manual 35
Functional Description
Functional Description
The 8920ADC Converts an analog audio stereo pair to a 48 KHz AES/EBU
signal. Refer to the block diagram in
Figure 9 while reading the following
functional description.
Figure 9. 8920ADC Block Diagram
Differential Input, Analog Gain and A/D Converters
The analog input is applied to a differential amplifier stage. This converts
the signal to single-ended and applies it to the coarse gain stage. Coarse
gain control pre-conditions the incoming signal before it is applied to the
A/D converters. For each channel, a six-position jumper sets the desired
coarse gain. This jumper controls the front-end pad of the unit in either a
-6 dB, -8 dB, or -12 dB mode and allows three 3 dB gain steps on the post
gain. This jumper allows input levels from +12 dBu to +28 dBu to be set to
0dBFS at the output.
The fine gain control is by two center-off toggle switches on the front of the
module. They provide a 6 dB range of fine gain adjustment in approxi-
mately 0.1 dB increments. The control takes approximately 6 to 10 seconds
to transition from minimum to maximum.
The signal is converted back to a differential signal and applied to the 24-bit
A/D converter, then to the Routing and Control FPGA (Field Program-
mable Gate Array).
0595_01
–
+
Right In
Level,
Clip,
Error,
PLL Lock,
Mode
LEDs
Differential
Input
Receivers
& Pad
Control bus
from backplane
Clocks
Audio
AES Out 1
AES Out 2
AES Out 3
AES Out 4
4-bit Rotary
Switch
Option
Jumpers (4)
- 12 dB
- 8 dB
- 6 dB
- 12 dB
- 8 dB
- 6 dB
Pad
–
+
Left In
Pad
- 12 dB
- 15 dB - 9 dB
- 12 dB
- 15 dB - 9 dB
Stereo
24-bit
ADC
FPGA
Routing and Control
Processor
CPU
(Controller)
AES
Receiver
and PLL AES Sync In
Test
Tone