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Sometimes, we want our amplifier to saturate. Below is a question based on a circuit that is designed to saturate very quickly.

Above is a Schmitt trigger. Notice that it has the same structure as an inverting amplifier except that the amplifier has been flipped so that the feedback resistor goes to the non$-$inverting terminal rather than the inverting terminal $($a mistake you may have made in completing the prelab$).$ This "positive feedback" causes the amplifier to saturate immediately upon receiving any input voltage. It is used in many applications, but its primary function is to compare the input voltage $($Vin$)$ to a reference voltage at its inverting input $($GND in the circuit above$).$ If the input voltage is greater than the reference voltage, the amplifier saturates to its most positive power rail. If the input voltage is less than the reference voltage, the amplifier saturates to its most negative power rail.$$

Below you will be given an input voltage, a voltage reference, and the power rail values. Match each given setup to the expected output.

Input Voltage $=-5$ V$,$ Reference voltage $=-10$ V$,$ Power Rails $=+/-15$ V$.$ Circuit will saturate to

Answer $1$ Question $1$Choose...$-15$ V$+15$ VGND$-12$V$+12$V$+5$V$-5$V

Input Voltage $=-5$ V$,$ Reference voltage $=-2$ V$,$ Power Rails $=+/-12$ V$.$ Circuit will saturate to

Answer $2$ Question $1$Choose...$-15$ V$+15$ VGND$-12$V$+12$V$+5$V$-5$V

Input Voltage $=4$ V$,$ Reference voltage $=6$ V$,$ Power Rails $=+/-15$ V$.$ Circuit will saturate to

Answer $3$ Question $1$Choose...$-15$ V$+15$ VGND$-12$V$+12$V$+5$V$-5$V

Input Voltage $=1$ V$,$ Reference voltage $=0$ V$,$ Power Rails $=+/-12$V$.$ Circuit will saturate to

Answer $4$ Question $1$Choose...$-15$ V$+15$ VGND$-12$V$+12$V$+5$V$-5$V

Question $2$

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You need an non$-$inverting amplifier with gain of $6$VV$6$VV$.$ Select the fewest number of resistors you would need to create this gain. $($Multiple choices can be selected$)$

Question $2$Select one or more:

a$.$

$2$ k$$

b$.$

$6$ k$$

c$.$

$10$ k$$

d$.$

$1$ k$$

e$.$

$3$ k$$

Question $3$

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An inverting amplifier has power rails of $20$V$20$V and a gain of $8$VV$8$VV$.$ At what input voltage would the amplifier begin to saturate?

Question $3$Select one:

a$.$

$400$ mV

b$.$

$20$ V

c$.$

$8$ V

d$.$

$2\mathrm{.}5$ V

Question $4$

Tries remaining: $2$

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You would like to build a custom speaker system for your cell phone. The signals from the headphone jack are GND$,$ Left Channel, and Right Channel.

You find a speaker test tone app that send a constant tone to each channel.

Turning the volume to its maximum setting, you measure the voltage between the Left Channel and GND to be $2$ V$.$ You see a similar voltage when you measure between the Right Channel and GND$.$

You will be connecting the left channel to an $8,50$ Watt speaker. You will connect the right channel to another $8,50$ Watt speaker.

Connecting the right or left channel, at maximum volume, directly to a speaker only gives:

of power.

In a $50$ Watt speaker, this isn't enough power to move the diaphragm $($no sound$).$

Assuming we want the speaker voltage to be in$-$phase with the phone voltage and we want $50$ Watts of power at maximum cell phone volume, what amplifier topology, gain, and power rails would be required for each channel?

NOTE: Don't try this at home!! Depending on your power rails, the amplifier would be required to dissipate $>50$ Watts of power. Most commercially available amplifiers will $($best case$)$ smoke and flame or $($worst case$)$ explode at this power level! For the LM$741$ amplifiers used in Lab $7,$ the maximum power is $500$ mW $($from datasheet$).50$ Watts is $100$X the maximum power level the amplifier can handle. In addition, the resistors used in the lab are rated at $0\mathrm{.}25$ Watts, so doing this experiment would cause catastrophic failure in every part of the circuit.