I just wondering how do you calculate the gain of the amplifier in a circuit like this:MAX446 CHIP

I am familiar with gain calculation on non-inverting and inverting opamp but am having trouble with this.

Any help would be appreciated.


This is actually a non-inverting op-amp with a pass band filter and a DC offset cancellation.

The formula is

Av = 1 + R2 / R1

Where the resistor are the 100k and 10k, so you would get a gain of 11.

  • The first group with 1 cap and 2 1Mohm resistor are a high pass filter and decoupling.
  • The 100pF below the chip is a low pass filter.
  • The 1uF below the 10k resistor is there to remove DC offset.
  • \$\begingroup\$ so that means that it will always have a 2.5v input? \$\endgroup\$ – Newbie Sep 30 '18 at 1:21
  • \$\begingroup\$ If the input bias current is zero (the input ESD structures have low leakage, and the input transistor is JFET or MOSFET), then YES. \$\endgroup\$ – analogsystemsrf Sep 30 '18 at 1:54
  • \$\begingroup\$ @analogsystemsrf wouldn't that mean that the output will always be 27.2V? \$\endgroup\$ – Newbie Sep 30 '18 at 2:12
  • \$\begingroup\$ That's the purpose of the 1uF cap, to remove DC offset, so only the signal will be amplified. I guess this is a solution to be able to use a single rail supply. The output cannot be higher than the opamp supply voltage. \$\endgroup\$ – Damien Sep 30 '18 at 2:15
  • \$\begingroup\$ @Damien so just to be clear this circuit can be used to amplifier the human voice to used in an ADC? \$\endgroup\$ – Newbie Sep 30 '18 at 2:19

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