Help me solve negative clip off in opamp ports

[danesh]

hi,

im tryin to make the input 2 to be bidirectional in term of signal flow which is a audio signal.

first: i input 1khz,1Vp sine signal in input 1 i can c a probe proper signal in input 2 and output 1.

second: i input signal in input 2 while input 1 left floating. The output in o/p port was negatife cliped off.

Can any one solve my negtive clip off prob Pls.

Thanks

 

[jonw0224]

OPAMP CLIP OFF

Put a capacitor between i/p 2 and the positive input of U2. Put a resistor from the negative input of U2 to V1 = 2.85V. Haven't tested or simulated it, but it should work.

 

[Kral]

Re: OPAMP CLIP OFF

Danesh,
You are depending on the DC output of U1 (2.85V) to bias U2 into its linear region. When you apply an input on i/p 2, the voltage divider that is formed from R3 and the source resistance of the signal source at i/p 2, pulls the DC bias on U2 below the input common mode range of U2.
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A more straighforward approach would be to make U2 an inverting summing amplifier.
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You could also capacitor couple i/p 2 to the non-inverting input of U@, as jonw0224 suggests, but you would need to have a source resistance << R3 to avoid AC loading and attenuation of the signal on i/p 2.
Regards,
Kral