## PHYS345 Electricity and Electronics

**Hint for S14-1**
The Thevenin resistance will change the effective value of the input resistance
in the inverting configuration.

**Hint for P14-1**

Refer to the weighted adder circuit. Detemine the variation needed in each input resistor
to obtain the desired effect.

**Hint for P14-2**

**Part 1.**
For the differential configuration,

v_{o} = R_{f}/R_{i} (v_{1} - v_{2})

If v_{o} = v_{1} + 5V is desired,
what should R_{f}/R_{i} and v_{2} be?

**Part 2.**
Use a voltage divider formed from two resistors R_{1} and R_{2} and
one of the available power supply voltages to craft a v_{2} input with the
same Thevenin equivalent as the answer to Part 1.

**Hint for P14-3**

Derive the gain of 100 from a differential configuration.
The input impedance of this part of the circuit will be R_{i}+R_{f}.
How can the remaining two op amps be used to increase the effective impedance seen by the
electrodes?

"http://www.physics.udel.edu/~watson/phys345/protected/exercises/hints/1117.html"

Last updated Dec. 1, 1998.

Copyright George Watson, Univ. of Delaware, 1998.