wm8982gefl-v Wolfson Microelectronics plc, wm8982gefl-v Datasheet - Page 61

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

Pre-Production
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Figure 38 Video Buffer with 0dB Gain
Figure 39 Video Buffer with 6dB Gain
CURRENT MODE OUTPUT
The current mode output employed by the WM8982 video buffer allows VBVDD to operate at lower
voltages than voltage mode video buffers, reducing power consumption, while the use of a current
reference resistor close to the WM8982 ensures 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), providing excellent
signal reproduction. Current mode output also provides inherent short circuit protection at the output.
The outputs VBREF and VBOUT are current mirrored transistors with a 5:1 ratio, so that:
i
A reference resistor (187R in above examples) is used for feedback on the video buffer amplifier via
the VBREF pin. The output current from VBOUT will be split between the source termination and
load termination (75R each in above examples).
Overall voltage gain (i.e. VBIN to TV input) is calculated as follows:
See applications note WAN-0166 for further information.
VBOUT
0
1
VBGAIN
(R40[1])
= 5 x i
VBREF
5 x (R
10 x (R
.
(SOURCE AND LOAD BOTH
LOADED GAIN FORMULA
TERMINATED WITH 75R)
LOAD
LOAD
|| R
|| R
SOURCE
SOURCE
) / R
) / R
VBREF
VBREF
0dB
+6dB
RSOURCE=75R;
LOADED GAIN
(VREF=187R;
RLOAD=75R)
PP, Rev 3.2, September 2008
+6dB
+12dB
UNLOADED GAIN
RSOURCE=75R;
(VREF=187R;
RLOAD=0)
WM8982
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