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Output getting distorted in push-pull circuit

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rishabh.anand

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i'm trying to work a powerline communication. for the TX side, the design has 3 filters...the first two form a 4rth order chebyshev filter and the last one is for current driving in low impedance loads
it consists of a push-pull ckt whose output is fed back to the op-amp to lower the crossover distortion

the output from the first two stages is perfect (6V p-p) but it distorts on the third stage ..pls help

the attached circuit is low on resolution so here are the values
Vpwr =10 V
input resistor=1K ohms
feedback resistance value = 4.02k ohms
load resistance =4.99 ohms
de-coupling capacitor=1 micro farad

the carrier frequency is 133Khz. for narrowband plc
the op-amps used are lmh 6639mf with disable
plus i wanted to tell tht there was complete noise in the output..unlike only crossover distortion of class-B operation.i'm also working on increasing the loop gain so as to rectify the problem...
 

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the attached circuit is low on resolution so here are the values
Yes. It would be really helpful to know the used OP types, but they can't be identified. Also the carrier frequency would be interesting.

Without more details, I expect, that the cross-over distortions are "normal operation" of the class B output stage. The OP would need considerable loop gain to reduce it.
 

You should set bias for output transistors
and maybe add small ohm resistors to emitters.

Like this

**broken link removed**

Regards KAK
 

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