Hello, I was wondering if you could help me with a project I have for school. I'm supposed to design a wien bridge oscillator but I'm not allowed to use an opamp, everything must be done using transistors.
I took the differential amplifier schematic from another electronics class and tested it with pspice to see if it works, and it does what it's supposed to in a simple configuration (it outputs the signal correctly and with the correct gain).
So far so good, but if I put it in a wien bridge configuration, no matter what values the RC network have, it oscillates around 1MHz with some distortion. I've tried a lot of things, including fiddling with the orcad simulator but to no avail. With the same settings (simulator and wien network) a database opamp (uA741) oscillates just fine, at the frequency set on the wien bridge. Therefore I'm guessing there's something wrong with the amplifier, but what?
I'm attaching the schematics and output/fft, maybe you can help...
I took the differential amplifier schematic from another electronics class and tested it with pspice to see if it works, and it does what it's supposed to in a simple configuration (it outputs the signal correctly and with the correct gain).
So far so good, but if I put it in a wien bridge configuration, no matter what values the RC network have, it oscillates around 1MHz with some distortion. I've tried a lot of things, including fiddling with the orcad simulator but to no avail. With the same settings (simulator and wien network) a database opamp (uA741) oscillates just fine, at the frequency set on the wien bridge. Therefore I'm guessing there's something wrong with the amplifier, but what?
I'm attaching the schematics and output/fft, maybe you can help...
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