WM8980CGEFL/RV WOLFSON [Wolfson Microelectronics plc], WM8980CGEFL/RV Datasheet - Page 73

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

Pre-Production
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Figure 41 Video Buffer with 0dB Gain
Figure 42 Video Buffer with 6dB Gain
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 3.8, May 2012
+6dB
+12dB
UNLOADED GAIN
RSOURCE=75R;
(VREF=187R;
RLOAD=0)
WM8980
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