Please expound on the discussion of open-loop gain linearity on page 10 of the OP77 Rev E datasheet. The write-up does not go into much detail and the plots confuse me. Both graphs plot some unknown voltage Vy versus the circuit output voltage Vx. What is the voltage, Vy? Perhaps if I had this information I'd understand why an ideal op amp would have a horizontal plot of Vy Vs. Vx (whatever Vy is).

My application requires a precision amplifier with no crossover distortion.

Thank you in advance for you help.

Hi,

Thank you for your interest in OP77. The Vx is the output voltage of the amplifier while Vy is the offset voltage (Vos) multiplied by a factor (since Vos is so small). Ideal operational amplifiers would have this Vx-Vy plot at a constant slope, the reciprocal of the slope being the open-loop gain. This means that for real op amps, the greater the variation of the slope, the greater the open-loop gain nonlinearity error. Figure 26 shows that OP77 has a excellent gain nonlinearity performance compared to typical precision op amps (Figure 25). MT-044 discusses this in detail.

Hope this helps! Let us know if you have other questions.

Best regards,

Neil