I've inherited a project where we require precise measurements of the "breaking" of a infrared beam. The first stage of the analog circuit is where I'm having problems. The circuit itself works, but isn't cost effective for manufacturing, so I'm trying to tweak it to prevent us from having to add components, and stop hand matching transistor / emiter pairs.
Essentitially the circuit is a voltage divider (R4 = 267k, R5 = 178k ) with a midpoint of 1v hooked to the + terminal of LMV774. As well, there is 0u47 cap to ground. The negative feedback Resistor (R6) can range from 10k to 330k (to bring the circuit into balance, which is 4v on the output), with a 470pF filter cap in parallel. Lastly on the input, before the Phototransistor there is 1.5k Resistor (R3). The emitter of the Phototransistor is connected to ground, and the collector is connected to R3.
The problem that I'm having is all of the formulas for calculating op-amp circuits that I've found all show a "current source" at the inverting imput, and we have a current drain. Any help on how to caculate out the values for this circuit would be appreciated.
The final wish of the circuit is to be able to select random pairs of emitters / transistors, populate them, and use 100k programmable pot to set the gain so that each pair falls into a usable region.
Essentitially the circuit is a voltage divider (R4 = 267k, R5 = 178k ) with a midpoint of 1v hooked to the + terminal of LMV774. As well, there is 0u47 cap to ground. The negative feedback Resistor (R6) can range from 10k to 330k (to bring the circuit into balance, which is 4v on the output), with a 470pF filter cap in parallel. Lastly on the input, before the Phototransistor there is 1.5k Resistor (R3). The emitter of the Phototransistor is connected to ground, and the collector is connected to R3.
The problem that I'm having is all of the formulas for calculating op-amp circuits that I've found all show a "current source" at the inverting imput, and we have a current drain. Any help on how to caculate out the values for this circuit would be appreciated.
The final wish of the circuit is to be able to select random pairs of emitters / transistors, populate them, and use 100k programmable pot to set the gain so that each pair falls into a usable region.