Considerations for audio codec design with sigma delta ADC

• Jul 30, 2004

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Vitamin-C

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sigma delta stability

Hi,

What things should be considered when design audio codec
with sigma delta ADC ?
What is the requirement of the opamp for example ?

thanks
vita

 

• Jul 30, 2004

• #2

opamp741

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Re: Audio sigma delta ADC

idle tones should not be there.
u can find the reason behind idle tones and the solution in the books.

 

• Aug 2, 2004

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bear7679

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Re: Audio sigma delta ADC

The most important thing about the OPAMP is the settling time and noise. The major noise source is 1/f noise.

 

• Aug 2, 2004

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Vitamin-C

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Re: Audio sigma delta ADC

Thank you.

What opamp architecture is good ?
How about cascode (with gain-boost) for a 3V supply?

any suggestion,
Vita

 

• Aug 2, 2004

• #5

opamp741

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Re: Audio sigma delta ADC

Opamp gain can be decided as 4 or 5 times of ur oversampling ratio..now it depends on ur technology that which topology will give u suitable gain..Casacode architecture will limiti ur opamp swing means ur integartor will saturate will quickly..keep all this tradeoffs in ur mind when selecting any architecture..

 

• Aug 3, 2004

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kyrandia

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Re: Audio sigma delta ADC

try to use folded cascode opamp . I think you don't need gain boost in audio sdm

 

• Aug 4, 2004

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bear7679

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Re: Audio sigma delta ADC

You can use telescope opamp if the dynamic range of the opamp's output is not large.

 

• Aug 4, 2004

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Vitamin-C

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Re: Audio sigma delta ADC

thank you

If I implemented in folded cascode, I need a
switch capacitor common mode feedback.

Does any one know how to simulate the AC response
with switched capacitor common mode feedback which
have two clocks input signal ??

thx in advance,
Vita

 

• Aug 4, 2004

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bear7679

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Re: Audio sigma delta ADC

I use resistor to replace the switch & capacitor, that means I use RC common mode feedback circuit in the ac analysis.

 

• Aug 5, 2004

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kyrandia

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Re: Audio sigma delta ADC

SpectreRF can deal with your problem, Try to use pss and pac analysis.

 

• Aug 5, 2004

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Vitamin-C

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Re: Audio sigma delta ADC

thanks for information

If possible could you show me an example how
to simulate a switched cap. circuit in SpectreRF.
I only used Hspice before, is the SpectreRF syntax very similar to Hspice ?

thank you.
Vita

 

• Oct 14, 2004

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emilian6

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Re: Audio sigma delta ADC

You can look at this guide:
**broken link removed**

 

• Oct 15, 2004

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Audio sigma delta ADC

Things to be considered for sigma-delta modulator design:
1. Sistem level
a) Signal Transfer function
b) Noise transfer function
c) Stability analysis if necessary
d) Sensitivity of these transfer functions to the system parameters.
2. Circuit Level
a) OPAMP Settling time
b) OPAMP Finite DC Gain
c) OPAMP SlewRate
d) OPAMP noise
e) Switch On-resistance effect
f) Path Mismatch
g) Integrator Mismatch
h) If it is multi-bit Dynamic Element Matching and
DAC nonlinearity
i) Noise sensitivity of different nodes