BioBuilding: Synthetic Biology for Students: Lab 3 Exploring Gain
Examining system behavior at different gain values
Resistance = 10 MΩ
Right now, the OpAmp's output and minus input are connected with a 10 MΩ resistor.
A circuit with very tight fully-on-or-fully-off behavior is more "digital", or switch-like, while a circuit where the LED can have a wide middle range of brightness is more "analog", or dial-like. The range of flashlight intensities that can hold the LED half-lit is a measure of the gain or strength of the amplifier. More precisely, the gain is the slope of the LED-output-vs.-photodiode-input line. Because the maximum brightness is the same for every circuit, a high-gain amplifier will cause the LED's brightness to max out even at a low level of input to the photodiode, whereas a low-gain amplifier will cause the LED's brightness to increase slowly before maxing out, as the photodiode input increases. We can tune this gain by changing the value of the gain resistor.
4. Sketch a graph with flashlight intensity on the x-axis and LED light intensity on the y-axis. At infinite resistance in place, is the circuit's behavior better described as a switch or a dial?
Resistance = 0Ω
Replace the 10MΩ resistor with a wire.
Resistance = infinite Ω
Remove the wire connecting the OpAmp's output to its negative input.