I need a linear amplifier to handle an extremely low level input signal of about 40 kHz, the operating frequency of the ultrasonic sensor, and I want to get a lot of circuit gain at very low cost and with good stability. The following SPICE models show what I have constructed and used. Each NPN level is biased by three of these resistors. This configuration, of course, no matter how high the transistor gain ß is, no one level can be saturated, and none of them can be turned off, so each level is guaranteed to be a positive gain element. In addition, since there is no signal feedback, as in the case of an operational amplifier, these levels cannot oscillate, but their non-oscillation stability is guaranteed. The results of the operation are as follows: The benefit of these designs is that there are no established limits on how many levels the circuit can include. I used four levels and got more than 100dB of gain, which is a lot, but there may be 5 levels, 6 levels... except for possible input noise, there is actually no limit, and eventually the last level Drive to an output noise level that is not expected. There are also components that have dependencies here. In the SPICE simulation, from 2N3904 transistors to 2N2222, we can see the dependencies: The ultrasonic detection system completed by the above circuit is very sensitive, and false intelligence is a problem. A friend looked at the oscilloscope, I climbed down the workbench, then moved my finger gently, and the oscilloscope's trajectory began to jump... Car Audio Player,Android Car Stereo,Universal Car Stereo,Android Music System Jiangmen soundrace electronics and technology co.,ltd. , https://www.soundracegroup.com
