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Osvaldo de Banfield 26th December 2011 03:59 PM

Help on op amps
Hi all guy´s. I want anybody can explain why a non inverting amplifier has a zero at the unity gain crossover point and why inverting doesn´t have it. I could´t find any good explanation at google. I had read it at the article "on RIAA Equalization networks" but I couldn´t understand why. Is there any pdf in which this fact is clearly explained??

Best regards. Thanks in advance.

Osvaldo, from Barrio Garay, Almirante Brown, Buenos Aires, Argentina.

AndrewT 27th December 2011 11:30 AM


godfrey 27th December 2011 12:24 PM

1 Attachment(s)
For RIAA equalization, you want the gain to decrease as frequency increases. However, with a non-inverting opamp circuit, the gain can not be less than one. So as frequency increases, the gain will reduce until it reaches unity, then level out, instead of reducing further. That gives the extra unwanted corner in the frequency response.

In the simple circuit below: Gain = (R1 + R2) / R1
Whatever values you choose, you can't make the gain less than unity. (For RIAA equalization, R2 would be replaced by an RC network)

Osvaldo de Banfield 27th December 2011 01:39 PM

AH, OK, very thanks. I think that there was a frequency rolloff inside the amplifier itself.

Osvaldo, from Barrio Garay, Almirante Brown, Buenos Aires, Argentina.

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