attenuator circuit

Question

Hello to every one, I hope you doing well. 
 I need some help about AD1937 inout. I have input signal with +24Dbu and differential.According to AD193X datasheet we cant source it to input directly so I design a attenuator circuit for input.Now I need your help for checking that circuit and tell me about its possible issues. Is there need to add ADC buffer circuit after this attenuator too?the green wave is output of circuit.Please help me about that.thanks

DaveThib · Accepted Answer

Hello ELEC23, 
 You will need to make some more adjustments but you are on the right track. You could add some buffers afterwards but I think you may not have to because the ADC input is not ground referenced. I suppose you can cap couple the output of this circuit would help. You can use the final passive filter shown in this applications circuit in the datasheet. 
 
 This will help with the situation of the common mode reference. You are using a 2.5V reference in your circuit. The ADC uses ~1.5V reference. This would really be running your amplifier circuit in a very inefficient way. I think you should just use ground as a reference and run both sides of this amp equally. Then cap couple the outputs to the ADC. 
 You will need to lower the voltage even more. Read this post where we discuss the full scale voltage levels the ADC is expecting. 
 AD1938 voltage range - Q&A - Audio - EngineerZone (analog.com) 
 
 The ADCs and the DACs on the AD1938 are the same as the AD1937. The AD1937 has I2C control rather than SPI. 
 Dave T)

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