Noninverting configuration (thing)

                      Rf
                         
                .--|     |----.
                |             |
                |      VCC    |
                |       |     |
          Ri    |  |\   |     |
                |  |  \ |     |
     .-|     |--+--|-   \     |
     |             |      >---+----VO
     |     VI -----|+   /
     |             |  / |
     |             |/   |
     |                  |
     |                 -VCC
     |        
0 V -+--------------------------------------o

V_O = output voltage
V_i = input voltage
V_CC = supply voltage

Another basic amplifier type, made using an operational amplifier (op amp for short). This circuit essentially takes an input voltage, multiplies it by a constant factor (A_V or voltage gain) and outputs that voltage. To work out the gain of a non-inverting amplifier, use the following formulae:

      VO         RF
AV = ---- = 1 + ----
      VI         RI

           RF
VO = (1 + ---- ) * VI = AV * VI
           RI

So, for instance, if you had a signal of two volts and you wanted to multiply this signal by five, you would wire the circuit up so that R_F was four times R_I. You might choose resistors of 250 KΩ (250 * 10³ ohms) and 1 MΩ (1 * 10⁶ ohms) respectively.

          250
AV = 1 + ----- = 1 + 4 = 5
         1000

VO = 5 * 2 = 10 V

The voltage at V_O would be 10 volts.

A special case of this is the voltage follower, where R_F is effectively zero. This results in the equation A_V = 1 + 0/R_I = 1. Hence, the output voltage is always equal to the input voltage, until saturation occurs (see below).

You can't get more power out of something than you put in, and the same is true for op amps. It is impossible for an op amp to output a higher voltage than its supply voltage (V_CC) and in most cases the highest voltage available is around 80% of V_CC. Therefore, it is important to make sure that the op amp's power supply inputs have a higher voltage than any expected output voltage. In the above example, a 12 volt supply (+/- 12 V) would be sufficient.

If you graphed V_I against V_O, the graph should be a straight line through the origin until a certain point, where the required output voltage exceeded the op amp's possible output. When the op amp is in this state it is said to be saturated either positively or negatively. Above this saturation point, V_O is no longer proportional to V_I.

Incidentally, this can provide some interesting effects using an amplifier with high gain and a wave-form (for instance a sine wave) input. A phenomenon known as clipping can be observed, where the peaks of the output waveform are squared off ('clipped'). This is often known in the area of sound amplification as overdrive or distortion.

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