Voltage Follower

OBJECTIVE:

To study the characteristic of an Op amp as a voltage follower.

THOERY:

Buffer amplifer: A buffer amplifier (sometimes simply called a buffer) is one that provides electrical impedance transformation from one circuit to another. Two main types of buffer exist: the voltage buffer and the current buffer.
Voltage buffer:A voltage buffer amplifier is used to transfer a voltage from a first circuit, having a high output impedance level, to a second circuit with a low input impedance level. The interposed buffer amplifier prevents the second circuit from loading the first circuit unacceptably and interfering with its desired operation.
Current buffer:A current buffer amplifier is used to transfer a current from a first circuit, having a low output impedance level, to a second circuit with a high input impedance level. The interposed buffer amplifier prevents the second circuit from loading the first circuit unacceptably and interfering with its desired operation

Op amp as a Voltage follower

A unity gain buffer amplifier may be constructed by applying a full series negative feedback (Fig. 1) to an op-amp simply by connecting its output to its inverting input, and connecting the signal source to the non-inverting input (Fig. 2). In this configuration, the entire output voltage (= 1 in Fig. 1) is placed contrary and in series with the input voltage. Thus the two voltages are subtracted according to KVL and their difference is applied to the op-amp differential input. This connection forces the op-amp to adjust its output voltage simply equal to the input voltage (Vout follows Vin )so the circuit is named op-amp voltage follower.

Used as a buffer amplifier to eliminate loading effects (e.g., connecting a device with a high source impedance to a device with a low input impedance).






Fig 1. A negative feedback amplifer


Fig 2. An op-amp–based unity gain buffer amplifier or op-amp as a VOLTAGE FOLLOWER

The importance of the circuit is due to the input and output impedances of the op-amp. The input impedance of the op-amp is very high, meaning that the input of the op-amp does not load down the source or draw any current from it. Because the output impedance of the op-amp is very low, it drives the load as if it were a perfect voltage source. Both the connections to and from the buffer are therefore bridging connections, which reduce power consumption in the source, distortion from overloading, crosstalk and other electromagnetic interference.

The voltage follower is often used for the construction of buffers for logic circuits.