wm8982gefl-v Wolfson Microelectronics plc, wm8982gefl-v Datasheet - Page 59

• Manufacturer Part Number: wm8982gefl-v
• Description: Mono Codec With Speaker Driver And Video Buffer
• Manufacturer: Wolfson Microelectronics plc

Pre-Production
VIDEO BUFFER
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DESCRIPTION
The WM8982 incorporates a current mode output video buffer capable of operating from a 2.5V
supply, with an input 3
programmed as 0dB or 6dB via the control interface. The current mode output means that the signal
swing seen at the output of the buffer will be the same as that at the connection to the receiving
equipment (e.g. a TV). Note that the input to the receiver should be AC coupled and terminated to
75Ω, as is standard, for best performance.
Figure 33 Video Buffer
The input clamp should be enabled when using AC coupling at the input to the video buffer, using the
VBCLAMPEN register bit.
Care should be taken with PCB layout, designing for at least 1GHz frequencies to avoid degrading
performance. Vias and sharp corners should be avoided and parasitic capacitance minimised on
signal paths, which should be kept as short and straight as possible. The VBVDD supply should be
decoupled as close to the pin as possible. See the “External Components” section for more
information.
LOW PASS FILTER
A low pass filter is integrated at the video buffer input, which is intended to remove images in the
video DAC output waveform at multiples of the DAC clock frequency. A 3
the following characteristics:
-10
-15
-20
-25
10
-5
5
0
10
rd
order Low Pass Filter (LPF) and clamp. The gain through this buffer can be
100
WM8982 Video Buffer Filter Response
-20dBV sinewave input, 0dB gain setting, VBVDD=3.3V
Frequency (kHz)
1000
PP, Rev 3.2, September 2008
10000
rd
order filter is used, with
WM8982
0dB
0dB Qboost
6dB
6dB Qboost
100000
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