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help designing an audio input amplifier (OPA1632) front end.

Yuval Izhaki
Prodigy 200 points
Other Parts Discussed in Thread: OPA1632

Dear Sir \ Madam

I am designing an audio product with the OPA1632 as an audio ADC front end connected as single ended to differential converter.

My requirement is as follow :

input signal level 3.6V P/P output signal level 2.4V P/P operating voltage +/-15V ,VCOM buffered and drive from the ADC and set to 2.5V  (P/P = peak to peak)

and required input impedance is 47Kohm. 

My problem is with the required input impedance.

I have try to use TI application note "Fully-Differential Amplifiers SLOA054D"  to design the Amplifier but the required input impedance want fit into the formulas provided.

My design schematic is similar to the schematic showed in the application section of the OPA1632 data sheet.  

Please help

Thank you

Yuval

  • 0
    TI__Genius 12631 points

    Hello,

     I have a couple of questions regarding your application:

    1. Are you using the circuit in Figure 12 of the datasheet with no termination resistance? If you could send me a schematic that would be great.

    2. With regards to the 47KOhm input resistance, is this the R1 and R2 resistors shown in Figure 11?

    -Samir

     

  • 0 in reply to Samir Cherian
    Prodigy 200 points

    Hi Samir

    Sorry for my late replay.

    I am using the circuit in figure 11 (DS REV 2010)

    No , it is not , Figure 12 show only generic connection

    Amplifier input impedance should be 47K  (AC respond)

  • 0 in reply to Yuval Izhaki
    TI__Genius 12631 points
    Ok, so from figure 11,
    1. Are you using a single-ended signal or a balanced(differential) input signal?
    2. If you have a fully-differential input signal then R1=R2=23.5KOhm will give you a 47Kohm differential input impedance @ dc.
    3. You mentioned ac response. The input impedance of the amplifier is 34MOhm in parallel with 4pF, so in the audio band this will still look like very high impedance and will not affect the input impedance set by R1 & R2.