![]() ![]() In both the inverting and non-inverting amplifiers only one input was used, the other input being connected to ground. ![]() Setting the value of closed loop gain is normally achieved by choosing the ratio of the feedback and input resistors. The voltage follower is therefore very useful as a buffer amplifier, that will reduce the loading effect on previous circuits and, because of its low output impedance will deliver more current to any following circuit. As with any other negative feedback (NFB) amplifier noise and distortion are also reduced. The input impedance of the circuit is increased to typically many megohms (10 6 Ω) or even teraohms (10 12 Ω) while the output impedance of the op amp remains very low, in the range of ohms to hundreds of ohms. The voltage follower uses 100% negative feedback that is effectively voltage derived and series fed, so the effect of the feedback on impedance is dramatic. Module 3.2 described how negative feedback can be used to increase the input impedance, and reduce the output impedance of an amplifier. The voltage follower does not therefore, act as an amplifier, the output voltage ‘follows’ the input voltage, but the circuit does have some very useful properties. In the voltage follower circuit however, both R in and R f are replace by simple conductors, and so both these values in the above formula will be extremely small, therefore the gain is 1. ![]()
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