DP 6-5 A microphone has an unloaded voltage  as shown in Figure DP 6-5 a.  An op-amp is available as shown in Figure DP 6-5 b.  It is desired to provide and output voltage of 4 V.  Design an inverting circuit and an non-inverting circuit and contrasts the input resistance at terminals x-y seen by the microphone.  Which configuration would you recommend in order to achieve good performance in spite of changes in the microphone resistance  ?

 

Hint: We plan to connect terminal a to terminal x and terminal b to terminal y or visa versa.

 

c06f115.eps

Figure DP 6-5

 

Standard inverting amplifier is

The output voltage is given by

 

 

Standard non-inverting amplifier is

The output voltage is given by

 

 

We need a gain of

 

Connecting microphone to inverting amplifier gives

Gain is found from

 

Let  and we can then solve for

 

 

Connecting microphone to non-inverting amplifier gives

 

 

Many possible choices, let

 

Note: Gain for inverting amp is

While for non-inverting amp gain is

 

So non-inverting amp does not have the resistance of microphone involved, so it is the better choice as amplifier for the microphone

 

For inverting amplifier one solution is

For non-inverting amplifier one solution is

Non-inverting amp is the better choice of amplifier!

 

 

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This page last updated on March 19, 2019