TDA1541A clocking and control questions

FunkyBits · 28th July 2010, 09:05 AM

I have a few questions regarding the TDA1541A chip I am investigating. It is in a piece of music kit so the digital signals will not be CD/Hi-Fi, thing is the audio is noisy and hence me taking a look and being here.

From inspection the TDA1541A is in "time MUX TWC" mode, SCK tied to Gnd, OB/TWC (pin 27) to 5V. BCK runs at 2.5MHz (400us), the WS runs at 29kHz (33.6us) and the 32 bit data stream comes in on pin 3 just after the +ve edge of WS (pulse of 5us).

I need to get my understanding correct so have a few basic questions if you will:-

Q1. When is the analogue output presented? It seems like both +/- edge of WS

Q2. If the output gets presented under the control of WS (29kHz) that suggest that is the playback sampling rate, nothing like the 44.1kHz of cd. Is my thinking correct?

Q3. If the sampling rate is 29kHz then the anti-aliasing filter needs to be about 15kHz of many pole (4+?), which contradicts the whole system spec. which is supposed to be CD quality.

Basic questions I know.

oshifis · 28th July 2010, 02:16 PM

I don't know if this helps:

http://www.datasheetcatalog.org/data...s/TDA1541A.pdf

"The converted samples appear at the output, at the first positive going transition of the bit clock signal after a negative going transition of the word select signal".

BCK has no influence on the output. It is WS that determines the sampling rate. It happened not once that I measured the period time on my oscilloscope in uncalibrated horizontal setting (just to fit one period on the screen), and calculating the frequency from the period time gave me incorrect value...

FunkyBits · 28th July 2010, 03:53 PM

Thanks for that, I did read my data sheets 1000 times, TDA1541 both March 85 and Feb 91, the one you refer to is TDA1541A and there it is!! (stuff about when data presented).

I took the timing detals with a logic analyzer fresh from servce lab who calibrates too and then confirmed with CRO, as you suggest easy to forget variable timebase knob is not at zero.

That's one mystery solved!

oshifis · 29th July 2010, 07:47 AM

Re Q2: Is WS 29 kHz or 44.1 kHz (or perhaps 176.3 kHz, 4x OS) then?

What is the model of this stuff?

28th July 2010, 09:05 AM	#1
FunkyBits diyAudio Member Join Date: Jul 2010	TDA1541A clocking and control questions I have a few questions regarding the TDA1541A chip I am investigating. It is in a piece of music kit so the digital signals will not be CD/Hi-Fi, thing is the audio is noisy and hence me taking a look and being here. From inspection the TDA1541A is in "time MUX TWC" mode, SCK tied to Gnd, OB/TWC (pin 27) to 5V. BCK runs at 2.5MHz (400us), the WS runs at 29kHz (33.6us) and the 32 bit data stream comes in on pin 3 just after the +ve edge of WS (pulse of 5us). I need to get my understanding correct so have a few basic questions if you will:- Q1. When is the analogue output presented? It seems like both +/- edge of WS Q2. If the output gets presented under the control of WS (29kHz) that suggest that is the playback sampling rate, nothing like the 44.1kHz of cd. Is my thinking correct? Q3. If the sampling rate is 29kHz then the anti-aliasing filter needs to be about 15kHz of many pole (4+?), which contradicts the whole system spec. which is supposed to be CD quality. Basic questions I know.

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28th July 2010, 02:16 PM	#2
oshifis diyAudio Member Join Date: Mar 2004 Location: Budapest, Hungary	I don't know if this helps: http://www.datasheetcatalog.org/data...s/TDA1541A.pdf "The converted samples appear at the output, at the first positive going transition of the bit clock signal after a negative going transition of the word select signal". BCK has no influence on the output. It is WS that determines the sampling rate. It happened not once that I measured the period time on my oscilloscope in uncalibrated horizontal setting (just to fit one period on the screen), and calculating the frequency from the period time gave me incorrect value...

28th July 2010, 03:53 PM	#3
FunkyBits diyAudio Member Join Date: Jul 2010	Thanks for that, I did read my data sheets 1000 times, TDA1541 both March 85 and Feb 91, the one you refer to is TDA1541A and there it is!! (stuff about when data presented). I took the timing detals with a logic analyzer fresh from servce lab who calibrates too and then confirmed with CRO, as you suggest easy to forget variable timebase knob is not at zero. That's one mystery solved!

29th July 2010, 07:47 AM	#4
oshifis diyAudio Member Join Date: Mar 2004 Location: Budapest, Hungary	Re Q2: Is WS 29 kHz or 44.1 kHz (or perhaps 176.3 kHz, 4x OS) then? What is the model of this stuff?

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