# Help with Op amp Circuit Design

Given the blue transfer function graph, I want to design a circuit that can replicate the characteristics, preferably using an op amp. This is what I have done: where the red circuit is the red curve So I just thought that the gain must be about 7, since that is the difference in dB. So using a non inverting amplifier I tried to correct the gain using the equation Gain=1+(R4/R3), and setting R3 to 3k ohms. It became even more off and I am even more confused! Any help or examples appreciated.

• And the pole frequency is 500hz?
– G36
Oct 12, 2019 at 10:26
• From looking at the blue curve data, I thought the pole/zero was 942Hz and 5654Hz (It is graphed in dB) Oct 12, 2019 at 10:39

Try this circuit configuration:

simulate this circuit – Schematic created using CircuitLab

Because form what I see you want a DC gain around $$\5.6 \:[V/V]\$$ and you want the HF gain to be 0dB (1 V/V).

And for this circuit, we have one pole at $$F_P = \frac{1}{2 \pi C_1 R_2 }$$

And the Zero at: $$F_Z = \frac{1}{2 \pi C_1 (R_1||R_2) }$$

• So what do you do with R3? Oct 12, 2019 at 10:54
• R3 sets the amplifier input resistance.
– G36
Oct 12, 2019 at 10:56
• So just confirming, the gain which you said was 5.6, is just the difference between the two graph lines? Oct 12, 2019 at 10:58
• On the blue plot, I see the gain around 15dB (at 10Hz) wich in linear scale is equal to 5.623...
– G36
Oct 12, 2019 at 11:01
• Oh ok thank you so much for your time! I hadn't ever heard of a resistor setting the amplifier input resistance before, so can you just set it to what ever you like since there is no equation, like what do you do in real life with it? Oct 12, 2019 at 11:04