the Vref of sigma delta ADC

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kuohsi

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switched capacitor adc vref

hi all, I am a rookie of this board.
Does anyone know what is the Vref which in the attached Figure?
and how many amplitude of Vref?
thank you!
 

sigma delta adc+ vref

kuohsi said:
hi all, I am a rookie of this board.
Does anyone know what is the Vref which in the attached Figure?
and how many amplitude of Vref?
thank you!
Click to expand...

Hi,
The Vref shown in the figure is the voltage associated with the feedback DAC.
If the output of the comparator is high, +Vref/2 is selected and fed back to the switched capacitor filter,and when the comparatpr output is low, -Vref/2 is fed back.
Usually, the voltage is multiplied by a feedback coefficient (implemented as capacitor ratios in a switched capacitor implementation.
The choice of Vref depends upon the supply voltage in the technology, implementation etc.

Hope that helps.

Bharath
 

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    kuohsi

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sigma delta adc+vref



Thank you for your answer
An extra question!!
Can I directly contect supply voltage (ex:5v) to Vref?
i.e. Vref=5v -Vref=-5v ?
 


Hi,
You can use supply voltage as Vref provided the amplifier can handle these voltage ranges. For ex, when you choose Vref to be +5 V, then that voltage goes as input to the operational amplifier in the figure (switched capacitor filter).
If there is any attenuation (ie, you implement a coefficient), then you can use supply voltage, else yuu might have use a different voltage.

Bharath
 

of course you cannt due to poor PSSR
 

hi,
vref of ADC produced from your reference voltage is better.
 

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