Dear Blog and fellow Blog frequenters,
This is my first entry and i wish to bitch while listening to the postal service, good pick fellas. So here goes, today my lab was a pain in the ass. We were trying to build a differential amplifier and we had ridiculous problems from the start. As we began our calculations we couldn't figure out how to get the resistor values to bias the third BJT so that the current source would output a constant 1mA. See, the problem was, we were working off a + supply of gnd and - supply of -12V, which through us all off. We couldn't figure out which base resistor to refernce the voltage divider with, but it turned out not to matter too much. See we finally figured out that we had to assume a Vce of approx. 6.5V, which gave us -.6V at the collector and 5v to spare across Ree. So Rb1 and Rb2 ended up being very close and it didn't matter which one was referenced. Anywho, we decided to build the darn thing an then the problems really started to come at us. Number one, which took us about an hour to figure out was that stupid Don Shaw put out some PNP's right next to the NPN's even though we weren't using the PNP's. So we assumed all the transistors were the same. So we built the circuit using two PNP's and one NPN. As it stood, half the circuit was trying to pull holes from places where there were a bunch of electrons and the other half was trying to pull electrons from a place where very few holes were being pumped and even fewer electrons, yah i know what you're thinki. Now this screwed up our bias levels, our Q points were up around 9V, when they were supposed to be at 6V, seriously, and then our common emmiter node was at +1.5V when it was supposed to be at -.6V. Anyway, we located the rogue transistors and eliminated them, making way for the proper NPN's to do their job and pump electrons into our circuit their by amplifying our input signal. Anyway, long story short, our circuit ended up working well after two hours, it had a common mode gain of .0089(very good) and a differential mode gain of about 40, and the gain didn;t drop off until we hit 100KHz, which is a nice range(audio range is 20Hz-20KHz). After that, i worked on my emag homework...for 3 hours. We had to find the motional e.m.f. and the transformer e.m.f. of a rectangular wire loop with a current through it in a rotating magnetic field, then we had to find the electrical and mechanical power, which were supposed to be equal, but somehow weren't. Anyway, long story short, we didn't finish and i don't know how to do even what we did finish. Now i must go to sleep, only to wake up and do more emag, some fourier series and fourier transforms and to top it all off i have to sit through statistics. So, I'm done, i hope you guys learned something about BJT's and the differences between NPN's and PNP's and i hope i did too. Finally, i bid thee adieu, and leave you with this: "I say, I want, I do. Everybody dance now. Why so serious, when it's only your life that's at stake?"
toot-a-loo
Pat
This is my first entry and i wish to bitch while listening to the postal service, good pick fellas. So here goes, today my lab was a pain in the ass. We were trying to build a differential amplifier and we had ridiculous problems from the start. As we began our calculations we couldn't figure out how to get the resistor values to bias the third BJT so that the current source would output a constant 1mA. See, the problem was, we were working off a + supply of gnd and - supply of -12V, which through us all off. We couldn't figure out which base resistor to refernce the voltage divider with, but it turned out not to matter too much. See we finally figured out that we had to assume a Vce of approx. 6.5V, which gave us -.6V at the collector and 5v to spare across Ree. So Rb1 and Rb2 ended up being very close and it didn't matter which one was referenced. Anywho, we decided to build the darn thing an then the problems really started to come at us. Number one, which took us about an hour to figure out was that stupid Don Shaw put out some PNP's right next to the NPN's even though we weren't using the PNP's. So we assumed all the transistors were the same. So we built the circuit using two PNP's and one NPN. As it stood, half the circuit was trying to pull holes from places where there were a bunch of electrons and the other half was trying to pull electrons from a place where very few holes were being pumped and even fewer electrons, yah i know what you're thinki. Now this screwed up our bias levels, our Q points were up around 9V, when they were supposed to be at 6V, seriously, and then our common emmiter node was at +1.5V when it was supposed to be at -.6V. Anyway, we located the rogue transistors and eliminated them, making way for the proper NPN's to do their job and pump electrons into our circuit their by amplifying our input signal. Anyway, long story short, our circuit ended up working well after two hours, it had a common mode gain of .0089(very good) and a differential mode gain of about 40, and the gain didn;t drop off until we hit 100KHz, which is a nice range(audio range is 20Hz-20KHz). After that, i worked on my emag homework...for 3 hours. We had to find the motional e.m.f. and the transformer e.m.f. of a rectangular wire loop with a current through it in a rotating magnetic field, then we had to find the electrical and mechanical power, which were supposed to be equal, but somehow weren't. Anyway, long story short, we didn't finish and i don't know how to do even what we did finish. Now i must go to sleep, only to wake up and do more emag, some fourier series and fourier transforms and to top it all off i have to sit through statistics. So, I'm done, i hope you guys learned something about BJT's and the differences between NPN's and PNP's and i hope i did too. Finally, i bid thee adieu, and leave you with this: "I say, I want, I do. Everybody dance now. Why so serious, when it's only your life that's at stake?"
toot-a-loo
Pat
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