Interfacing PIC Microcontrollers

The universal amplifier can have any number of inputs and outputs, but to

make the mathematical model as simple as possible, we will set the following

conditions:

• the number of inverting inputs is equal to the number of non-inverting in-

puts

• the input resistors (R

i

) are all equal

• the feedback resistors (R

f

) are equal

By summing the current at the op-amp input terminals, we can show that

V

0

= R

f

/R

i

(V

2

+ V

4

+ V

6

+ …) − (V

1

+ V

3

+ V

5

+ …)

The output voltage is given by the arithmetic sum of the input voltages

multiplied by the gain, where the non-inverting (+) inputs are even numbered

and the inverting (−) odd. The amplifier then behaves as a combination ...