WM8980CGEFL/RV WOLFSON [Wolfson Microelectronics plc], WM8980CGEFL/RV Datasheet - Page 70

• Manufacturer Part Number: WM8980CGEFL/RV
• Description: Stereo CODEC with Speaker Driver and Video Buffer
• Manufacturer: WOLFSON [Wolfson Microelectronics plc]

WM8980
VIDEO BUFFER
w
Table 53 Unused Output Pin Tie-off Options
DESCRIPTION
Figure 36 Video Buffer
LOW PASS FILTER
The WM8980 incorporates a current mode output video buffer capable of operating from a 2.5V
supply, with an input 3
programmed as 0dB or 6dB (=6dB or 12dB unloaded) 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 75, as is standard, for best performance.
The input clamp should be enabled when using AC coupling at the input to the video buffer, using the
VBCLAMPEN register bit.
Note: The WM8980 Video Buffer input signal level at the input pin (VBIN) should not exceed 500mV
when using ac coupling or 330mV when using dc coupling when the input clamp circuit is enabled.
It is therefore recommended that the video signal is ac coupled into the video buffer and that the
video signal driving VBIN is disabled and is either high impedance or GND when the video buffer is
disabled.
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.
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
used, with the following characteristics:
L/ROUT2EN/
OUT3/4EN
0
0
0
0
1
1
rd
OUT3BOOST/
OUT4BOOST/
SPKBOOST
order Low Pass Filter (LPF) and clamp. The gain through this buffer can be
0
0
1
1
0
1
VROI
X
X
0
1
0
1
1kΩ tie-off to AVDD/2
30kΩ tie-off to AVDD/2
1kΩ tie-off to 1.5xAVDD/2
30kΩ tie-off to 1.5xAVDD/2
Output enabled (DC level=AVDD/2)
Output enabled (DC level=1.5xAVDD/2)
OUTPUT CONFIGURATION
rd
order Butterworth filter is
PP, Rev 3.8, May 2012
Pre-Production
70