r5717 - trunk/gta02-core/docs/ecn

rehar at docs.openmoko.org rehar at docs.openmoko.org
Sat Nov 28 21:12:05 CET 2009

Author: rehar
Date: 2009-11-28 21:12:05 +0100 (Sat, 28 Nov 2009)
New Revision: 5717

- added C3017 (1uF) change to ECN0033 
- rewrote ECN0019 to reflect Joergs changes, reopened for further discussion
- added ECN0042, switch to symmetrical microphone configuration 

Modified: trunk/gta02-core/docs/ecn/STATUS
--- trunk/gta02-core/docs/ecn/STATUS	2009-11-27 23:31:03 UTC (rev 5716)
+++ trunk/gta02-core/docs/ecn/STATUS	2009-11-28 20:12:05 UTC (rev 5717)
@@ -18,7 +18,7 @@
 0016	Done	Remove upper acceleration sensor (U7801)
 0017	Done	Move Bluetooth module (U2) to main PCB
 0018	Cancel	Add beads/filters to audio signals leaving/entering can
-0019	Done	Consider applying buzz fix
+0019	Discuss	Consider applying buzz fix
 0020	Cancel	No common mode choke on stereo signals (B4102)
 0021	Defer	Use EMI-hardened microphone (MC4301)
 0022	Done	Apply bass fix
@@ -41,6 +41,7 @@
 0039	Discuss	Insert 0R resistors into SPI signals
 0040	Discuss	Remove backup battery (BAT1701)
 0041	Discuss	Test points and 0R resistors for camera interface
+0042	Discuss	Changing internal microphone to symmetrical configuration
 Open ECNs
@@ -51,6 +52,7 @@
 0008	GPS
 0010	AUDIO
 0011	USB
+0019	AUDIO
 0024	GPS
 0026	SD-SIM
 0027	General
@@ -61,3 +63,5 @@
 0039	CPU, LCM
 0040	PMU, MODEM
 0041	CPU
+0042    AUDIO

Modified: trunk/gta02-core/docs/ecn/ecn0019.txt
--- trunk/gta02-core/docs/ecn/ecn0019.txt	2009-11-27 23:31:03 UTC (rev 5716)
+++ trunk/gta02-core/docs/ecn/ecn0019.txt	2009-11-28 20:12:05 UTC (rev 5717)
@@ -4,17 +4,23 @@
 RF feeds into the microphone line of the headset jack JK4401. This RF causes
 ripples on the microphone bias line of the codec which leads to a poor audio
 quality of the microphone.
-One goal of the ECN0018 is to prevent any RF from reaching the wolfson codec,
+One goal of ECN0018 is to prevent any RF from reaching the wolfson codec,
 therefore this problem would be solved. However in GTA02-A7 this issue was
-taken care of by adding C4306/C4307 to the microphone lines. Those caps are
-still defined as NC but the footprint(1206) is big enough so that a 100uF cap
-can be easily mounted if necessary. Also R4303 is interchangeable with a 2.2k
-resistor as mentioned in the big-C Buzz Fix [1].
+taken care of by adding C4306/C4307 to the microphone lines [1].
-I'd consider to leave those cap footprints in the circuit if the solution with
-the beads fails and we still get ripple on the mic bias line.
+C4306 in conjunction with R4305(2.2k) acts as a low-pass filter and keeps
+any RF from entering the internal microphone path. It would be a good idea to 
+move C4307 before R4305 to protect against RF entering the MICBIAS line at all.
+However to be on the save side we could add a 0R resistor(R4310) in series to 
+be able to switch back to the current configuration if necessary. 
+I also would consider removing the C4307 footprint completely because it does not
+participate in a noise cancellation when RF is entering the microphone path 
+through MICBIAS.
+Despite the above changes we still leave the C4306 footprint unpopulated. This 
+is just a pre-emptive fix if ECN0018 does not archive the expected effect.
 [1] http://people.openmoko.org/joerg/GSM_EMI_noise/big-C_rework_SOP_rc2.pdf

Modified: trunk/gta02-core/docs/ecn/ecn0033.txt
--- trunk/gta02-core/docs/ecn/ecn0033.txt	2009-11-27 23:31:03 UTC (rev 5716)
+++ trunk/gta02-core/docs/ecn/ecn0033.txt	2009-11-28 20:12:05 UTC (rev 5717)
@@ -11,6 +11,7 @@
 - C3007 and C3006 (GSM modem input)
 - C3018 and C3011 (GSM modem output)
 - C3016 and C4406 (headset MIC)
+- C3017 (ACOP/ACIN coupling)
 [1] http://www.wolfsonmicro.com/uploads/documents/en/WM8753.pdf (p. 88)

Added: trunk/gta02-core/docs/ecn/ecn0042.txt
--- trunk/gta02-core/docs/ecn/ecn0042.txt	                        (rev 0)
+++ trunk/gta02-core/docs/ecn/ecn0042.txt	2009-11-28 20:12:05 UTC (rev 5717)
@@ -0,0 +1,16 @@
+Changing internal microphone to symmetrical configuration
+According to Joerg, the internal microphone was switched to an asymmetrical 
+configuration in GTA02-Rev06. It was expected that this would influence the 
+noise (Buzz) dramatically. However a real improvement of the noise could not be
+In most cases a symmetrical configuration offers a better common mode noise 
+rejection than an asymmetrical one. Therefore it is prefered to operate the 
+internal microphone in a symmetrical configuration.
+	- replace R4304 with a 2k2 resistor
+Author Rene Harder <rehar at saweb.de>

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