# Op-Amp Voltage Follower With Bootstrap

The bias path can compromise the high input impedance you would otherwise get with an op-amp as with transistors amplifiers. This particularly with ac-coupled inputs where a resistor to ground is mandatory. The bootstrap circuit shown below is a possible solution if that is a problem.

The 1mF capacitor makes the upper 100k resistor look like a high impedance current source to input signals as in the transistor bootstrap circuit. The low frequency roll-off for this circuit will begin at about 10Hz. The response will drop at 12dB per octave tor frequencies somewhat below this where both capacitors contribute to the roll-off.