r5198 - trunk/gta02-core/docs/ecn

rehar at docs.openmoko.org rehar at docs.openmoko.org
Mon Jun 22 20:45:22 CEST 2009

Author: rehar
Date: 2009-06-22 20:45:22 +0200 (Mon, 22 Jun 2009)
New Revision: 5198

started ecn removing audio amplifier

Modified: trunk/gta02-core/docs/ecn/ecn0010.txt
--- trunk/gta02-core/docs/ecn/ecn0010.txt	2009-06-22 17:02:04 UTC (rev 5197)
+++ trunk/gta02-core/docs/ecn/ecn0010.txt	2009-06-22 18:45:22 UTC (rev 5198)
@@ -1 +1,30 @@
 Remove audio amplifier (U4101)
+The Wolfson codec is able to drive a mono 8 OHM speaker so there is no need for
+a separate power amplifier. Therefore the output section of the audio subsystem
+gets heavily reconstructed.
+Removing the external amplifier (U4101) as well as the amplifier specific
+components R4114, R4112, R4109, R4108, R4110, R4113, C4117, C4111, C4110, C4110
+and C4115. Also there is no need for the AMP_SHUTDOWN and HP_IN signals anymore, the external
+speaker and headphone can be fully controlled by the corresponding register settings of the
+codec. (see [1])
+The GTA02 earpiece will be connected between OUT3 and ROUT1 of the codec, there will be
+no change on the filter and bypass capacitors.
+The external speaker will be connected directly between ROUT2 and LOUT2.
+Filter and capacitors will be the same.
+[1] http://www.wolfsonmicro.com/uploads/documents/en/WM8753.pdf
+- Headphone switch to GPIO4
+- massive change of components (C4405,R4405 etc) headphone jack,
+  improve audio quality for low impedance headsets at low frequencies
+- reason for varistor on EP_L line
+- maybe increase the pull down resistors (R4117 and R4116) for high 
+  impedance headphones (Z >= 2k OHM).
\ No newline at end of file

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